Add command syntax highlighting.

- And other minor fixes/cleanup.

include/bed.h

@@ -18,8 +18,8 @@ struct BEd {
   internal::functions::Function eof_op;
   std::array<std::optional<internal::functions::Suffix>, 26> suffixes;
   internal::theme::Theme theme;
-  std::unordered_map<std::string, internal::syntax::Language> languages;
-  internal::io::IO &io;
+  std::unordered_map<std::string, internal::syntax::Language *> languages;
+  internal::io::IO io;
   internal::vase::AppendStorage append{"/tmp"};
 
   bool help_mode = false;
@@ -39,7 +39,7 @@ struct BEd {
   internal::buffer::Range prev_2;
   internal::marks::MarksEngine marks;
 
-  BEd(std::vector<std::string> args, internal::io::IO &io);
+  BEd(std::vector<std::string> args);
   ~BEd();
 
   internal::buffer::Buffer &buffer(const std::string &);
@@ -47,6 +47,7 @@ struct BEd {
   internal::buffer::Range &prev();
   void mark(uint8_t, internal::buffer::Line);
 
+  void print_help();
   void handle(std::string_view cmd, bool eof);
   void run();
   void suffix_handle(char s);

include/definitions.h

@@ -15,17 +15,4 @@ struct fatal_error : std::runtime_error {
 struct ed_error : std::runtime_error {
   ed_error(std::string msg) : std::runtime_error(msg) {}
 };
-
-struct Highlight {
-  enum : uint8_t {
-    None = 0,
-    Bold = 1 << 0,
-    Italic = 1 << 1,
-    Strikethrough = 1 << 2,
-    Underline = 1 << 3,
-  };
-  uint32_t fg;
-  uint32_t bg;
-  uint8_t flags;
-};
 } // namespace bed

include/internal/buffer/buffer.h

@@ -1,6 +1,5 @@
 #pragma once
 
-#include "clip.h"
+#include "./types/clip.h"
+#include "./types/generic.h"
 #include "decl.h"
-#include "generic.h"
-#include "pch.h"

include/internal/buffer/decl.h

@@ -10,7 +10,7 @@ namespace bed::internal::buffer {
 struct Buffer {
   enum struct Kind : uint8_t {
     Generic,
-    Null,
+    History,
     Clip,
     Cancel,
     Shell,
@@ -26,7 +26,7 @@ struct Buffer {
   std::string name;
 
   explicit Buffer(std::string name, Kind kind)
-      : kind(kind), state(Unmodified), name(name) {};
+      : kind(kind), state(Unmodified), name(std::move(name)) {};
   virtual ~Buffer() = default;
 
   virtual bool waste() = 0;
@@ -43,6 +43,7 @@ struct Buffer {
   virtual void join(BEd &ctx, uint64_t start_line, uint64_t end_line) = 0;
   virtual void remove(BEd &ctx, uint64_t start_line, uint64_t end_line) = 0;
   virtual void append(BEd &ctx, vase::Shard *text, uint64_t line) = 0;
+  virtual void replace(BEd &ctx, vase::Shard *text, uint64_t start_line, uint64_t end_line) = 0;
   virtual void print(BEd &ctx, uint64_t start_line, uint64_t end_line) = 0;
   virtual void number_print(BEd &ctx, uint64_t start_line, uint64_t end_line) = 0;
   virtual void list_print(BEd &ctx, uint64_t start_line, uint64_t end_line) = 0;

include/internal/buffer/generic.h

@@ -1,39 +0,0 @@
-#pragma once
-
-#include "decl.h"
-#include "pch.h"
-
-namespace bed::internal::buffer {
-struct GenericBuffer : Buffer {
-  vase::Shard *root;
-  std::filesystem::path save_path{};
-  std::string language{};
-  std::optional<syntax::Parser> parser{};
-
-  GenericBuffer(std::string name)
-      : Buffer(name, Kind::Generic), root(nullptr) {};
-  ~GenericBuffer();
-
-  bool waste() override;
-  uint64_t lines() override;
-  uint64_t bytes() override;
-  void load(BEd &ctx, vase::Shard *text) override;
-  void set_filename(std::filesystem::path path) override;
-  std::filesystem::path filename() override;
-  vase::Shard *copy(uint64_t start_line, uint64_t end_line) override;
-  void substitute(
-    BEd &ctx, uint64_t start_line, uint64_t end_line,
-    std::string &regex, std::string &replacement, std::string &options
-  ) override;
-  void join(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
-  void remove(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
-  void append(BEd &ctx, vase::Shard *text, uint64_t line) override;
-  void print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
-  void number_print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
-  void list_print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
-  uint64_t next_closing(uint64_t start) override;
-  uint64_t prev_closing(uint64_t start) override;
-  uint64_t find_next(std::string_view pattern, uint64_t start) override;
-  uint64_t find_prev(std::string_view pattern, uint64_t start) override;
-};
-} // namespace bed::internal::buffer

include/internal/buffer/types/clip.h

@@ -1,7 +1,6 @@
 #pragma once
 
-#include "decl.h"
-#include "pch.h"
+#include "../decl.h"
 
 namespace bed::internal::buffer {
 struct ClipBuffer : Buffer {
@@ -24,6 +23,7 @@ struct ClipBuffer : Buffer {
   void join(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
   void remove(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
   void append(BEd &ctx, vase::Shard *text, uint64_t line) override;
+  void replace(BEd &ctx, vase::Shard *text, uint64_t start_line, uint64_t end_line) override;
   void print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
   void number_print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
   void list_print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;

include/internal/buffer/types/generic.h

@@ -0,0 +1,46 @@
+#pragma once
+
+#include "../decl.h"
+#include "history.h"
+#include "shard.h"
+
+namespace bed::internal::buffer {
+struct HistoryItem {
+  syntax::ParserSnapshot parse_state;
+  vase::Shard *text;
+  std::chrono::system_clock::time_point timestamp;
+  std::string summary;
+};
+
+struct GenericBuffer : ShardBuffer {
+  uint64_t base_version{0};
+  std::chrono::system_clock::time_point timestamp;
+  std::string action;
+  std::filesystem::path save_path{};
+  std::vector<HistoryItem> undo_stack;
+  std::vector<HistoryItem> redo_stack;
+
+  GenericBuffer(std::string name)
+      : ShardBuffer(name, nullptr, nullptr, Kind::Generic) {}
+  ~GenericBuffer();
+
+  void list_history(BEd &ctx);
+  HistoryBuffer *get_history(uint64_t version);
+  void snapshot(std::string action);
+  bool undo(BEd &ctx);
+  bool redo(BEd &ctx);
+  uint64_t prune(int);
+  bool waste() override;
+  void load(BEd &ctx, vase::Shard *text) override;
+  void set_filename(std::filesystem::path path) override;
+  std::filesystem::path filename() override;
+  void substitute(
+    BEd &ctx, uint64_t start_line, uint64_t end_line,
+    std::string &regex, std::string &replacement, std::string &options
+  ) override;
+  void join(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
+  void remove(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
+  void append(BEd &ctx, vase::Shard *text, uint64_t line) override;
+  void replace(BEd &ctx, vase::Shard *text, uint64_t start_line, uint64_t end_line) override;
+};
+} // namespace bed::internal::buffer

include/internal/buffer/types/history.h

@@ -0,0 +1,39 @@
+#pragma once
+
+#include "../decl.h"
+#include "shard.h"
+
+namespace bed::internal::buffer {
+struct HistoryBuffer : ShardBuffer {
+  HistoryBuffer(
+    std::string name, vase::Shard *root,
+    const syntax::ParserSnapshot &snapshot
+  ) : ShardBuffer(std::move(name), root, snapshot, Kind::History) {}
+
+  bool waste() override {
+    return true;
+  }
+  void load(BEd &, vase::Shard *) override {
+    throw ed_error("History buffers are read-only.");
+  }
+  void set_filename(std::filesystem::path) override {}
+  std::filesystem::path filename() override {
+    return {};
+  }
+  void substitute(BEd &, uint64_t, uint64_t, std::string &, std::string &, std::string &) override {
+    throw ed_error("History buffers are read-only.");
+  }
+  void join(BEd &, uint64_t, uint64_t) override {
+    throw ed_error("History buffers are read-only.");
+  }
+  void remove(BEd &, uint64_t, uint64_t) override {
+    throw ed_error("History buffers are read-only.");
+  }
+  void append(BEd &, vase::Shard *, uint64_t) override {
+    throw ed_error("History buffers are read-only.");
+  }
+  void replace(BEd &, vase::Shard *, uint64_t, uint64_t) override {
+    throw ed_error("History buffers are read-only.");
+  }
+};
+} // namespace bed::internal::buffer

include/internal/buffer/types/shard.h

@@ -0,0 +1,42 @@
+#pragma once
+
+#include "../decl.h"
+
+namespace bed::internal::buffer {
+struct ShardBuffer : Buffer {
+  vase::Shard *root;
+  syntax::ParserSnapshot parse{};
+
+  ShardBuffer(std::string name, vase::Shard *root, syntax::Language *language, Kind kind)
+      : Buffer(std::move(name), kind), root(root) {
+    vase::Shard::retain(root);
+    if (language)
+      parse = syntax::make_parser(root, lines(), language);
+  }
+  ShardBuffer(
+    std::string name,
+    vase::Shard *root,
+    const syntax::ParserSnapshot &snapshot,
+    Kind kind
+  ) : Buffer(std::move(name), kind),
+      root(root),
+      parse(syntax::retain(snapshot)) {
+    vase::Shard::retain(root);
+  }
+  ~ShardBuffer() {
+    vase::Shard::release(root);
+    syntax::release(parse);
+  }
+
+  uint64_t lines() override;
+  uint64_t bytes() override;
+  vase::Shard *copy(uint64_t start_line, uint64_t end_line) override;
+  void print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
+  void number_print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
+  void list_print(BEd &ctx, uint64_t start_line, uint64_t end_line) override;
+  uint64_t next_closing(uint64_t start) override;
+  uint64_t prev_closing(uint64_t start) override;
+  uint64_t find_next(std::string_view pattern, uint64_t start) override;
+  uint64_t find_prev(std::string_view pattern, uint64_t start) override;
+};
+} // namespace bed::internal::buffer

include/internal/io/io.h

@@ -2,6 +2,7 @@
 
 #include "definitions.h"
 #include "pch.h"
+#include "tokens.h"
 
 namespace bed::internal::io {
 struct KeyEvent {
@@ -57,13 +58,27 @@ struct IO {
   static void enable_raw();
   static volatile std::atomic_bool resized;
   static void handle_sigwinch(int);
+  BEd &bed;
 
-  IO();
+  static enum struct Mode {
+    PIPE,
+    TERMINAL
+  } mode;
+
+  std::string pipe_input;
+  std::deque<char> input_queue;
+
+  IO(BEd &);
   ~IO();
 
   IO(const IO &) = delete;
   IO &operator=(const IO &) = delete;
 
+  bool interactive() const {
+    return mode == Mode::TERMINAL;
+  }
+  void apply(const io::Token::Kind &t);
+  void reset();
   void enable_mouse();
   void disable_mouse();
 
@@ -71,14 +86,14 @@ struct IO {
   std::pair<uint16_t, uint16_t> cursor_position();
   void move_cursor(uint16_t row, uint16_t col);
 
+  std::pair<std::string, bool> read_pipe();
+
   KeyEvent read_key();
   void write(const char *, uint64_t);
   void write(std::string_view);
   void write_line(std::string_view);
   void run_pty(const std::string &);
 
-  std::deque<char> input_queue;
-
   KeyEvent::ReadResult get_next_byte(char &out);
   void enqueue_bytes(const std::string &bytes);
   static int utf8_seq_len(uint8_t byte);

include/internal/io/tokens.h

@@ -0,0 +1,105 @@
+#pragma once
+
+#include "definitions.h"
+#include "pch.h"
+
+namespace bed::internal::io {
+struct Token {
+  uint64_t start;
+  uint64_t end;
+  enum Kind : uint8_t {
+    TempCurrent,
+    BufferName,
+    AddressSeperator,
+    Address,
+    Offset,
+    AddressRegex,
+    AddressSymbol,
+    Number,
+    Mark,
+    RubyFunction,
+    RubyArg,
+    Function,
+    Any,
+    Shell,
+    Ruby,
+    File,
+    Replacement,
+    Suffix,
+    Color1,
+    Color2,
+    Color3,
+    Color4,
+    Color5,
+    Warning,
+    Data,
+    Shebang,
+    Comment,
+    Error,
+    String,
+    Escape,
+    Interpolation,
+    Regexp,
+    True,
+    False,
+    Char,
+    Keyword,
+    KeywordOperator,
+    Operator,
+    Namespace,
+    Class,
+    Module,
+    Type,
+    Constant,
+    VariableInstance,
+    VariableGlobal,
+    Annotation,
+    Directive,
+    Label,
+    Brace1,
+    Brace2,
+    Brace3,
+    Brace4,
+    Brace5,
+    Heading1,
+    Heading2,
+    Heading3,
+    Heading4,
+    Heading5,
+    Heading6,
+    Blockquote,
+    List,
+    ListItem,
+    Code,
+    LanguageName,
+    LinkLabel,
+    ImageLabel,
+    Link,
+    Table,
+    TableHeader,
+    Italic,
+    Bold,
+    Underline,
+    Strikethrough,
+    HorizontalRule,
+    Tag,
+    Attribute,
+    CheckDone,
+    CheckNotDone,
+    Count
+  } type;
+};
+
+struct Highlight {
+  enum : uint8_t {
+    None = 0,
+    Bold = 1 << 0,
+    Italic = 1 << 1,
+    Strikethrough = 1 << 2,
+    Underline = 1 << 3,
+  };
+  uint32_t fg;
+  uint32_t bg;
+  uint8_t flags;
+};
+} // namespace bed::internal::io

include/internal/marks/marks.h

@@ -22,7 +22,7 @@ struct MarksEngine {
         continue;
       if (marks[i].number == UINT64_MAX)
         continue;
-      if (marks[i].number >= start)
+      if (marks[i].number > start)
         marks[i].number += count;
     }
   }

include/internal/parser/parser.h

@@ -85,12 +85,12 @@ struct Parser {
   std::string_view cmd;
   uint16_t i;
   Command *command;
-  std::vector<ui::Token> *tokens;
+  std::vector<io::Token> *tokens;
   CompletionContext *completion;
 
   explicit Parser(
     std::string_view cmd, BEd &bed, Command *command,
-    std::vector<ui::Token> *tokens, CompletionContext *completion
+    std::vector<io::Token> *tokens, CompletionContext *completion
   );
 
   char peek(uint16_t = 0); // == \0 if at eof.
@@ -107,7 +107,7 @@ struct Parser {
   void operation();
 
   void parse();
-
+  static std::vector<io::Token> get_highlight(std::string_view cmd, BEd &bed);
   static Command get_command(std::string_view, BEd &);
   static std::vector<AddressPromise> get_addresses(std::string_view cmd, BEd &bed);
 };

include/internal/syntax/decl.h

@@ -1,73 +1,11 @@
 #pragma once
 
+#include "internal/io/tokens.h"
 #include "internal/trie/trie.h"
+#include "internal/vase/vase.h"
 #include "pch.h"
 
 namespace bed::internal::syntax {
-struct Token {
-  uint32_t start;
-  uint32_t end;
-  enum Kind : uint8_t {
-    Data,
-    Shebang,
-    Comment,
-    Error,
-    String,
-    Escape,
-    Interpolation,
-    Regexp,
-    Number,
-    True,
-    False,
-    Char,
-    Keyword,
-    KeywordOperator,
-    Operator,
-    Function,
-    Namespace,
-    Class,
-    Module,
-    Type,
-    Constant,
-    VariableInstance,
-    VariableGlobal,
-    Annotation,
-    Directive,
-    Label,
-    Brace1,
-    Brace2,
-    Brace3,
-    Brace4,
-    Brace5,
-    Heading1,
-    Heading2,
-    Heading3,
-    Heading4,
-    Heading5,
-    Heading6,
-    Blockquote,
-    List,
-    ListItem,
-    Code,
-    LanguageName,
-    LinkLabel,
-    ImageLabel,
-    Link,
-    Table,
-    TableHeader,
-    Italic,
-    Bold,
-    Underline,
-    Strikethrough,
-    HorizontalRule,
-    Tag,
-    Attribute,
-    CheckDone,
-    CheckNotDone,
-    Count
-  } type;
-};
-
 struct ParseEvent {
   uint8_t closing;
   ParseEvent(uint8_t t) : closing(t) {}
@@ -75,7 +13,11 @@ struct ParseEvent {
 
 struct Language {
   std::function<void *()> none_state;
-  std::function<void(void **, std::string_view, bool, std::vector<Token> *, std::vector<ParseEvent> *)> parse;
+  std::function<void(
+    void **, std::string_view,
+    bool, std::vector<io::Token> *, std::vector<ParseEvent> *
+  )>
+    parse;
   std::function<void *(void *)> copy;
   std::function<bool(void *, void *)> equal;
   std::function<void(void *)> destroy;
@@ -85,35 +27,125 @@ struct ParseState {
   static constexpr uint64_t BRANCH_BIT = 1ull << 63;
   static constexpr uint64_t LINES_MASK = ~BRANCH_BIT;
   uint64_t header;
+  uint16_t height;
+  std::atomic_uint16_t refs;
   bool is_branch() const {
     return header & BRANCH_BIT;
   }
   uint64_t lines() const {
     return header & LINES_MASK;
   }
+  explicit ParseState(bool branch, uint64_t lines, uint16_t height)
+      : height(height), refs(1) {
+    header = lines;
+    header |= branch * BRANCH_BIT;
+  };
+  static void retain(ParseState *node);
+  static void release(Language &lang, ParseState *node);
+  static ParseState *build(Language &lang, ParseState **pieces, uint64_t lo, uint64_t hi);
+  static ParseState *splice(
+    Language &lang, ParseState *node, vase::Shard *vase,
+    uint64_t line, uint64_t original, uint64_t final
+  );
+  static ParseState *concat(Language &lang, ParseState *a, ParseState *b);
 };
 
 struct ParseStateBranch : ParseState {
   ParseState *left;
   ParseState *right;
+  ParseStateBranch(ParseState *l, ParseState *r)
+      : ParseState(
+          true, l->lines() + r->lines(),
+          1 + std::max(l->height, r->height)
+        ),
+        left(l), right(r) {
+    retain(l);
+    retain(r);
+  }
 };
 
 struct ParseStateLeaf : ParseState {
-  void *state;
-  uint32_t n;
-  uint32_t cap;
-  uint16_t *blocks;
+  static constexpr uint64_t MAX_CHUNK = 512;
+  uint32_t n{0};
   static constexpr uint16_t IS_CLOSING = 0x8000;
   static constexpr uint16_t LINE_MASK = 0x7fff;
+  uint16_t *blocks{nullptr};
+  void *state;
+  ParseStateLeaf(void *state, uint64_t lines, uint32_t n, uint16_t *blocks_)
+      : ParseState(false, lines, 1), n(n), state(state) {
+    blocks = (uint16_t *)malloc(sizeof(uint16_t) * n);
+    memcpy(blocks, blocks_, sizeof(uint16_t) * n);
+  };
+};
+
+struct ParsePieceBuilder {
+  Language &lang;
+  std::vector<ParseState *> pieces;
+  std::vector<uint16_t> blocks;
+  void *piece_state{nullptr};
+  uint64_t chunk_start{0};
+  uint64_t chunk_lines{0};
+  ParsePieceBuilder(Language &lang, uint64_t first_line)
+      : lang(lang), chunk_start(first_line) {}
+  void add(
+    void *state,
+    uint64_t line,
+    const std::vector<ParseEvent> &events
+  ) {
+    if (chunk_lines == 0) {
+      chunk_start = line;
+      piece_state = lang.copy(state);
+    }
+    for (const auto &ev : events) {
+      blocks.push_back(
+        (ev.closing ? ParseStateLeaf::IS_CLOSING : 0)
+        | (line - chunk_start)
+      );
+    }
+    ++chunk_lines;
+    if (chunk_lines == ParseStateLeaf::MAX_CHUNK)
+      flush();
+  }
+  void flush() {
+    if (chunk_lines == 0)
+      return;
+    pieces.push_back(new ParseStateLeaf(
+      piece_state,
+      chunk_lines,
+      blocks.size(),
+      blocks.data()
+    ));
+    piece_state = nullptr;
+    blocks.clear();
+    chunk_lines = 0;
+  }
+  ParseState *finish() {
+    flush();
+    if (pieces.empty())
+      return nullptr;
+    ParseState *root = ParseState::build(lang, pieces.data(), 0, pieces.size());
+    pieces.clear();
+    return root;
+  }
 };
 
 struct TreeCursor {
+  Language &lang;
+  ParseState *root;
   ParseStateLeaf *leaf = nullptr;
   ParseStateBranch *stack[64];
   uint8_t depth = 0;
   bool went_left[64];
-  TreeCursor(ParseState *root, uint64_t target_line, uint64_t *relative);
+  TreeCursor(
+    Language &lang, ParseState *root,
+    uint64_t target_line, uint64_t *relative
+  );
+  ~TreeCursor();
+  TreeCursor(const TreeCursor &) = delete;
+  TreeCursor &operator=(const TreeCursor &) = delete;
   void next();
   void prev();
+  ParseState *prefix();
+  ParseState *suffix();
 };
 } // namespace bed::internal::syntax

include/internal/syntax/parser.h

@@ -1,57 +1,54 @@
 #pragma once
 
 #include "decl.h"
-#include "internal/vase/vase.h"
 #include "pch.h"
 
 namespace bed::internal::syntax {
-struct Parser {
-  static constexpr uint64_t MAX_CHUNK = 512;
+struct ParserSnapshot {
+  ParseState *root = nullptr;
+  Language *lang = nullptr;
+};
 
-  ParseState *root;
-  Language lang;
-  bool in_edit = false;
+ParserSnapshot make_parser(vase::Shard *vase, uint64_t lines, Language *lang);
+ParserSnapshot retain(const ParserSnapshot &snap);
+void release(ParserSnapshot &snap);
+
+uint64_t next_closing(const ParserSnapshot &snap, uint64_t line);
+uint64_t prev_opening(const ParserSnapshot &snap, uint64_t line);
+
+struct Iterator {
+  ParserSnapshot snap;
+  std::optional<vase::Iterator> it;
+  void *state;
+  uint64_t at;
+  std::vector<io::Token> tokens;
+  std::vector<ParseEvent> events;
+  Iterator(uint64_t, ParserSnapshot, vase::Shard *);
+  ~Iterator();
+  Iterator(const Iterator &) = delete;
+  Iterator &operator=(const Iterator &) = delete;
+  Iterator(Iterator &&other);
+  Iterator &operator=(Iterator &&other);
+  void next();
+};
+
+std::optional<Iterator> get_hl(const ParserSnapshot &snap, vase::Shard *vase, uint64_t target);
+
+void insert(ParserSnapshot &snap, vase::Shard *vase, uint64_t start, uint64_t count);
+void erase(ParserSnapshot &snap, vase::Shard *vase, uint64_t start, uint64_t count);
+
+struct Edit {
+  ParserSnapshot *target;
   bool dirty = false;
   uint64_t dirty_start = 0;
   uint64_t dirty_end = 0;
+  int64_t edit_delta = 0;
 
-  Parser(vase::Shard *, uint64_t, Language);
-  ~Parser();
-  Parser(const Parser &) = delete;
-  Parser &operator=(const Parser &) = delete;
+  explicit Edit(ParserSnapshot &snap) : target(&snap) {}
 
-  void reset(vase::Shard *, uint64_t, Language);
-  void erase(vase::Shard *, uint64_t, uint64_t);
-  void insert(vase::Shard *, uint64_t, uint64_t);
-  void modify(vase::Shard *, uint64_t, uint64_t);
-
-  void begin_edit();
-  void erase(uint64_t start, uint64_t count);
-  void insert(uint64_t start, uint64_t count);
-  void end_edit(vase::Shard *vase);
   void mark_dirty(uint64_t start, uint64_t end);
-
-  uint64_t next_closing(uint64_t line);
-  uint64_t prev_opening(uint64_t line);
-
-  std::pair<ParseState *, ParseState *> split_tree(ParseState *node, uint64_t line);
-  ParseState *join_tree(ParseState *a, ParseState *b);
-
-  struct Iterator {
-    Parser *p;
-    std::optional<vase::Iterator> it;
-    void *state;
-    uint64_t at;
-    std::vector<Token> tokens;
-    std::vector<ParseEvent> events;
-    Iterator(uint64_t, Parser *, vase::Shard *);
-    ~Iterator();
-    Iterator(const Iterator &) = delete;
-    Iterator &operator=(const Iterator &) = delete;
-    Iterator(Iterator &&other);
-    Iterator &operator=(Iterator &&other);
-    void next();
-  };
-  std::optional<Iterator> get_hl(vase::Shard *, uint64_t);
+  void insert(uint64_t start, uint64_t count);
+  void erase(uint64_t start, uint64_t count);
+  void commit(vase::Shard *vase);
 };
 } // namespace bed::internal::syntax

include/internal/syntax/ruby/parser.h

@@ -104,6 +104,6 @@ struct RubyParser {
 
 void ruby_parse(
   void **v_state, std::string_view line, bool first_line,
-  std::vector<Token> *tokens, std::vector<ParseEvent> *events
+  std::vector<io::Token> *tokens, std::vector<ParseEvent> *events
 );
 } // namespace bed::internal::syntax::ruby

include/internal/theme/theme.h

@@ -6,11 +6,11 @@
 
 namespace bed::internal::theme {
 struct Theme {
-  std::array<Highlight, internal::syntax::Token::Count> hl;
+  std::array<io::Highlight, io::Token::Count> hl;
 
   Theme();
 
-  Highlight get(internal::syntax::Token token) const;
+  io::Highlight get(const io::Token::Kind &token) const;
 
   static Theme default_theme();
   static Theme from_name(std::string_view name);

include/internal/ui/command.h

@@ -4,31 +4,6 @@
 #include "pch.h"
 
 namespace bed::internal::ui {
-struct Token {
-  enum struct Type : uint8_t {
-    TempCurrent,      // @
-    AddressSeperator, // ; ,
-    Address,          // . $ % [ ] ^ ~
-    Offset,           // +N -N + -
-    AddressRegex,     // /re/ ?re?
-    AddressSymbol,    // >s> <s< <s>
-    Number,           // 10
-    Mark,             // 'm
-    RubyFunction,     // (func:arg)
-    RubyArg,
-    Function,
-    Any,
-    Shell,
-    Ruby,
-    File,
-    Regex,
-    Replacement,
-    Suffix
-  } type;
-  uint16_t start;
-  uint16_t end;
-};
-
 struct CommandIO {
   std::string cmd;
   uint16_t cursor;
@@ -41,6 +16,8 @@ struct CommandIO {
 
   CommandIO(BEd &);
   std::pair<std::string, bool> run();
+  std::pair<std::string, bool> run_pipe();
+  std::pair<std::string, bool> run_terminal();
   void redraw();
 };
 } // namespace bed::internal::ui

include/internal/ui/text_mode.h

@@ -15,7 +15,9 @@ struct TextMode {
 
   TextMode(BEd &);
   std::pair<vase::Shard *, bool> run();
-  void grow(size_t required_height);
+  std::pair<vase::Shard *, bool> run_pipe();
+  std::pair<vase::Shard *, bool> run_terminal();
+  void grow();
   void redraw();
 };
 } // namespace bed::internal::ui

include/internal/vase/shard.h

@@ -12,13 +12,13 @@ struct Shard {
     Petal
   } kind;
 
-  uint8_t height;
+  uint16_t height;
   std::atomic_uint32_t refs;
 
   uint64_t length;
   uint64_t lines;
 
-  Shard(Kind kind, uint64_t length, uint64_t lines, uint8_t height)
+  Shard(Kind kind, uint64_t length, uint64_t lines, uint16_t height)
       : kind(kind), height(height), refs(1), length(length), lines(lines) {};
 
   static void retain(Shard *n);
@@ -62,5 +62,4 @@ struct Petal : Shard {
     source->retain();
   };
 };
-
 } // namespace bed::internal::vase

include/internal/vase/vase.h

@@ -48,6 +48,7 @@ std::string to_string(Shard *root, Range range);
 
 Shard *insert(AppendStorage *ap, Shard *root, Shard *text, uint64_t line);
 Shard *erase(Shard *root, uint64_t start, uint64_t end);
+Shard *replace(Shard *root, Shard *text, uint64_t start, uint64_t end);
 Shard *join(Shard *root, uint64_t start, uint64_t end);
 Shard *copy(Shard *root, uint64_t start, uint64_t end);
 void write_file(std::filesystem::path path, Shard *text);

src/bed/run.cc

@@ -2,11 +2,8 @@
 #include "internal/parser/parser.h"
 
 namespace bed {
-BEd::BEd(std::vector<std::string> args, internal::io::IO &io)
-    : theme(internal::theme::Theme::default_theme()), io(io) {
-  internal::functions::Function::register_posix(*this);
-  internal::functions::Function::register_extented(*this);
-  internal::functions::Suffix::register_suffixes(*this);
+BEd::BEd(std::vector<std::string> args)
+    : theme(internal::theme::Theme::default_theme()), io(*this) {
   std::string prompt_ = "";
   std::string file = "";
   bool suppress = false;
@@ -20,6 +17,9 @@ BEd::BEd(std::vector<std::string> args, internal::io::IO &io)
       suppress = true;
     } else if (args[i] == "-v" || args[i] == "--verbose") {
       help_mode = true;
+    } else if (args[i] == "-h" || args[i] == "--help") {
+      print_help();
+      throw fatal_error("", 0);
     } else {
       if (file.size())
         throw fatal_error("Invalid arguments given.", 1);
@@ -31,6 +31,10 @@ BEd::BEd(std::vector<std::string> args, internal::io::IO &io)
   else
     prompt_mode = false;
   suppress_mode = suppress;
+  internal::functions::Function::register_posix(*this);
+  internal::functions::Function::register_extented(*this);
+  internal::functions::Suffix::register_suffixes(*this);
+  languages["ruby"] = new internal::syntax::Language(internal::syntax::ruby::lang_ruby());
   buffers["clip"] = new internal::buffer::ClipBuffer("clip");
   current() = {"default", 0};
   try {
@@ -47,6 +51,12 @@ BEd::BEd(std::vector<std::string> args, internal::io::IO &io)
 BEd::~BEd() {
   for (auto &[_, buffer] : buffers)
     delete buffer;
+  for (auto &[_, lang] : languages)
+    delete lang;
+}
+
+void BEd::print_help() {
+  io.write("BEd - A line editor.\n");
 }
 
 void BEd::run() {
@@ -56,9 +66,11 @@ void BEd::run() {
     try {
       handle(cmd, eof);
     } catch (ed_error &e) {
+      io.apply(internal::io::Token::Warning);
       io.write_line("?");
       if (help_mode)
         io.write_line(e.what());
+      io.reset();
       last_help = e.what();
     }
   }
@@ -162,9 +174,47 @@ void BEd::handle(std::string_view cmd, bool eof) {
 internal::buffer::Buffer &BEd::buffer(const std::string &name) {
   if (name.empty())
     throw ed_error("can't have empty buffer name");
-  auto it = buffers.find(name);
-  if (it != buffers.end())
-    return *it->second;
+  {
+    auto it = buffers.find(name);
+    if (it != buffers.end())
+      return *it->second;
+  }
+  constexpr std::string_view prefix = "history/";
+  if (name.starts_with(prefix)) {
+    std::string_view path{name};
+    path.remove_prefix(prefix.size());
+    auto slash = path.rfind('_');
+    if (slash == std::string_view::npos || slash == 0 || slash == path.size() - 1)
+      throw ed_error("invalid history");
+    std::string bufname(path.substr(0, slash));
+    auto version_str = path.substr(slash + 1);
+    std::size_t version;
+    try {
+      version = std::stoull(std::string(version_str));
+    } catch (...) {
+      throw ed_error("invalid history version");
+    }
+    auto it = buffers.find(bufname);
+    if (it != buffers.end()) {
+      auto &buf_ = *it->second;
+      if (buf_.kind != internal::buffer::Buffer::Kind::Generic)
+        throw ed_error("Only normal buffers can have history.");
+      auto &buf = *(internal::buffer::GenericBuffer *)&buf_;
+      auto *history_buf = buf.get_history(version);
+      buffers.emplace(name, history_buf);
+      return *history_buf;
+    }
+    throw ed_error("Buffer has no history.");
+  }
+  for (auto &c : name)
+    if (!(('0' <= c && c <= '9')
+          || ('a' <= c && c <= 'z')
+          || ('A' <= c && c <= 'Z')
+          || c == '-' || c == '_'
+          || c == '+' || c == '.'
+          || c == ',' || c == '$'
+          || c == '/' || c == '~'))
+      throw ed_error("Invalid buffer name.");
   auto *buf = new internal::buffer::GenericBuffer(name);
   buffers.emplace(name, buf);
   return *buf;

src/internal/buffer/generic.cc

@@ -3,27 +3,211 @@
 
 namespace bed::internal::buffer {
 GenericBuffer::~GenericBuffer() {
+  for (auto &item : undo_stack) {
+    syntax::release(item.parse_state);
+    vase::Shard::release(item.text);
+  }
+  for (auto &item : redo_stack) {
+    syntax::release(item.parse_state);
+    vase::Shard::release(item.text);
+  }
+}
+
+void GenericBuffer::list_history(BEd &ctx) {
+  uint64_t current = base_version + undo_stack.size();
+  for (size_t i = 0; i < undo_stack.size(); ++i) {
+    auto &item = undo_stack[i];
+    uint64_t version = base_version + i;
+    auto time = std::chrono::system_clock::to_time_t(item.timestamp);
+    std::tm tm = *std::localtime(&time);
+    ctx.io.write_line(
+      std::format(
+        "  {}  {:04}-{:02}-{:02} {:02}:{:02}:{:02} {}",
+        version,
+        tm.tm_year + 1900,
+        tm.tm_mon + 1,
+        tm.tm_mday,
+        tm.tm_hour,
+        tm.tm_min,
+        tm.tm_sec,
+        item.summary
+      )
+    );
+  }
+  {
+    auto time = std::chrono::system_clock::to_time_t(timestamp);
+    std::tm tm = *std::localtime(&time);
+    ctx.io.write_line(
+      std::format(
+        "* {}  {:04}-{:02}-{:02} {:02}:{:02}:{:02} {}",
+        current,
+        tm.tm_year + 1900,
+        tm.tm_mon + 1,
+        tm.tm_mday,
+        tm.tm_hour,
+        tm.tm_min,
+        tm.tm_sec,
+        action
+      )
+    );
+  }
+  for (size_t i = 0; i < redo_stack.size(); ++i) {
+    auto &item = redo_stack[redo_stack.size() - 1 - i];
+    uint64_t version = current + i + 1;
+    auto time = std::chrono::system_clock::to_time_t(item.timestamp);
+    std::tm tm = *std::localtime(&time);
+    ctx.io.write_line(
+      std::format(
+        "  {}  {:04}-{:02}-{:02} {:02}:{:02}:{:02} {}",
+        version,
+        tm.tm_year + 1900,
+        tm.tm_mon + 1,
+        tm.tm_mday,
+        tm.tm_hour,
+        tm.tm_min,
+        tm.tm_sec,
+        item.summary
+      )
+    );
+  }
+}
+
+HistoryBuffer *GenericBuffer::get_history(uint64_t version) {
+  uint64_t current = base_version + undo_stack.size();
+  if (version < base_version)
+    throw ed_error("History version has been pruned.");
+  if (version < current) {
+    auto &item = undo_stack[version - base_version];
+    return new HistoryBuffer(name, item.text, item.parse_state);
+  }
+  if (version == current)
+    return new HistoryBuffer(name, root, parse);
+  uint64_t redo_offset = version - current - 1;
+  if (redo_offset >= redo_stack.size())
+    throw ed_error("No such history version.");
+  auto &item = redo_stack[redo_stack.size() - 1 - redo_offset];
+  return new HistoryBuffer(name, item.text, item.parse_state);
+}
+
+void GenericBuffer::snapshot(std::string action_) {
+  if (base_version == 0) {
+    base_version++;
+  } else {
+    vase::Shard::retain(root);
+    undo_stack.push_back(
+      HistoryItem{
+        syntax::retain(parse),
+        root,
+        timestamp,
+        action
+      }
+    );
+  }
+  for (auto &item : redo_stack) {
+    syntax::release(item.parse_state);
+    vase::Shard::release(item.text);
+  }
+  redo_stack.clear();
+  timestamp = std::chrono::system_clock::now();
+  action = action_;
+}
+
+bool GenericBuffer::undo(BEd &ctx) {
+  if (undo_stack.empty())
+    return false;
+  HistoryItem prev = undo_stack.back();
+  undo_stack.pop_back();
+  vase::Shard::retain(root);
+  redo_stack.push_back(
+    HistoryItem{
+      syntax::retain(parse),
+      root,
+      timestamp,
+      action
+    }
+  );
   vase::Shard::release(root);
+  root = prev.text;
+  syntax::release(parse);
+  parse = prev.parse_state;
+  timestamp = prev.timestamp;
+  action = prev.summary;
+  state = Modified;
+  if (!root) {
+    ctx.prev().buffername = name;
+    ctx.prev().start = 0;
+    ctx.prev().end = 0;
+  } else {
+    ctx.prev().buffername = name;
+    ctx.prev().start = 1;
+    ctx.prev().end = root->lines + 1;
+  }
+  return true;
+}
+
+bool GenericBuffer::redo(BEd &ctx) {
+  if (redo_stack.empty())
+    return false;
+  HistoryItem next = redo_stack.back();
+  redo_stack.pop_back();
+  vase::Shard::retain(root);
+  undo_stack.push_back(
+    HistoryItem{
+      syntax::retain(parse),
+      root,
+      timestamp,
+      action
+    }
+  );
+  vase::Shard::release(root);
+  root = next.text;
+  syntax::release(parse);
+  parse = next.parse_state;
+  timestamp = next.timestamp;
+  action = next.summary;
+  state = Modified;
+  if (!root) {
+    ctx.prev().buffername = name;
+    ctx.prev().start = 0;
+    ctx.prev().end = 0;
+  } else {
+    ctx.prev().buffername = name;
+    ctx.prev().start = 1;
+    ctx.prev().end = root->lines + 1;
+  }
+  return true;
+}
+
+uint64_t GenericBuffer::prune(int keep) {
+  size_t drop =
+    undo_stack.size() > (size_t)keep
+      ? undo_stack.size() - keep
+      : 0;
+  for (size_t i = 0; i < drop; ++i) {
+    syntax::release(undo_stack[i].parse_state);
+    vase::Shard::release(undo_stack[i].text);
+  }
+  undo_stack.erase(
+    undo_stack.begin(),
+    undo_stack.begin() + drop
+  );
+  base_version += drop;
+  for (auto &item : redo_stack) {
+    syntax::release(item.parse_state);
+    vase::Shard::release(item.text);
+  }
+  redo_stack.clear();
+  return undo_stack.size();
 }
 
 bool GenericBuffer::waste() {
   return save_path.empty()
-         && root == nullptr;
-}
-
-uint64_t GenericBuffer::lines() {
-  if (root)
-    return root->lines + 1;
-  return 0;
-}
-
-uint64_t GenericBuffer::bytes() {
-  if (root)
-    return root->length + 1;
-  return 0;
+         && root == nullptr
+         && undo_stack.empty();
 }
 
 void GenericBuffer::load(BEd &ctx, vase::Shard *text) {
+  snapshot("Load file.");
   if (lines())
     ctx.marks.erase(name, 1, lines());
   vase::Shard::release(root);
@@ -39,7 +223,9 @@ void GenericBuffer::load(BEd &ctx, vase::Shard *text) {
     ctx.prev().start = 1;
     ctx.prev().end = text->lines + 1;
   }
-  parser.emplace(root, lines(), syntax::ruby::lang_ruby());
+  ctx.current() = {name, lines()};
+  syntax::release(parse);
+  parse = syntax::make_parser(root, lines(), ctx.languages["ruby"]);
 }
 
 void GenericBuffer::set_filename(std::filesystem::path path) {
@@ -51,35 +237,73 @@ std::filesystem::path GenericBuffer::filename() {
 };
 
 void GenericBuffer::append(BEd &ctx, vase::Shard *text, uint64_t line) {
+  if (!text)
+    return;
+  snapshot(std::format("Insert {} lines after line {}", text->lines + 1, line));
   ctx.prev().buffername = name;
   ctx.prev().start = line + 1;
   ctx.prev().end = line + text->lines + 1;
+  ctx.current() = {name, line + text->lines + 1};
   root = vase::insert(&ctx.append, root, text, line);
-  ctx.marks.insert(name, ctx.prev().start, ctx.prev().end);
-  if (parser)
-    parser->insert(root, ctx.prev().start, ctx.prev().end);
+  ctx.marks.insert(name, line, text->lines + 1);
+  if (parse.lang)
+    syntax::insert(parse, root, line, text->lines + 1);
   state = Modified;
 }
 
 void GenericBuffer::remove(BEd &ctx, uint64_t start_line, uint64_t end_line) {
+  snapshot(std::format("Remove lines {} to {}", start_line, end_line));
   root = vase::erase(root, start_line, end_line);
   ctx.prev().buffername = name;
-  ctx.prev().start = std::min(start_line, lines());
-  ctx.prev().end = std::min(start_line, lines());
+  uint64_t l = std::min(start_line, lines());
+  ctx.prev().start = l;
+  ctx.prev().end = l;
+  ctx.current() = {name, l};
   ctx.marks.erase(name, start_line, end_line - start_line + 1);
-  if (parser)
-    parser->erase(root, start_line, end_line - start_line + 1);
+  if (parse.lang)
+    syntax::erase(parse, root, start_line, end_line - start_line + 1);
+  state = Modified;
+}
+
+void GenericBuffer::replace(BEd &ctx, vase::Shard *text, uint64_t start_line, uint64_t end_line) {
+  if (!text) {
+    remove(ctx, start_line, end_line);
+    return;
+  }
+  snapshot(std::format("Replace lines {} to {} with {} lines", start_line, end_line, text->lines));
+  ctx.prev().buffername = name;
+  ctx.prev().start = start_line;
+  ctx.prev().end = start_line + text->lines;
+  ctx.current() = {name, start_line + text->lines};
+  uint64_t new_count = text->lines + 1;
+  uint64_t old_count = end_line - start_line + 1;
+  root = vase::replace(root, text, start_line, end_line);
+  if (parse.lang) {
+    syntax::Edit edit(parse);
+    edit.erase(start_line, old_count);
+    edit.insert(start_line, new_count);
+    edit.commit(root);
+  }
+  if (new_count > old_count) {
+    uint64_t diff = new_count - old_count;
+    ctx.marks.insert(name, end_line, diff);
+  } else if (new_count < old_count) {
+    uint64_t diff = old_count - new_count;
+    ctx.marks.collapse(name, start_line + new_count - 1, diff);
+  }
   state = Modified;
 }
 
 void GenericBuffer::join(BEd &ctx, uint64_t start_line, uint64_t end_line) {
+  snapshot(std::format("Join lines {} to {}", start_line, end_line));
   root = vase::join(root, start_line, end_line);
   ctx.prev().buffername = name;
   ctx.prev().start = start_line;
   ctx.prev().end = start_line;
+  ctx.current() = {name, start_line};
   ctx.marks.collapse(name, start_line, end_line - start_line);
-  if (parser)
-    parser->erase(root, start_line, end_line - start_line);
+  if (parse.lang)
+    syntax::erase(parse, root, start_line, end_line - start_line);
   state = Modified;
 }
 
@@ -87,11 +311,13 @@ void GenericBuffer::substitute(
   BEd &ctx, uint64_t start_line, uint64_t end_line,
   std::string &regex, std::string &replacement, std::string &options
 ) {
+  snapshot(std::format("Substitute /{}/ with /{}/ in lines {} to {}", regex, replacement, start_line, end_line));
   ctx.prev().buffername = name;
   ctx.prev().start = start_line;
   ctx.prev().end = end_line;
-  if (parser)
-    parser->begin_edit();
+  std::optional<syntax::Edit> edit;
+  if (parse.lang)
+    edit.emplace(parse);
   root = vase::substitute(
     &ctx.append,
     root,
@@ -103,168 +329,19 @@ void GenericBuffer::substitute(
     [&](uint64_t line, uint64_t old_lines, uint64_t new_lines) {
       if (old_lines) {
         ctx.marks.erase(name, line, old_lines);
-        if (parser)
-          parser->erase(line, old_lines);
+        if (edit)
+          edit->erase(line, old_lines);
       }
       if (new_lines) {
-        ctx.marks.insert(name, line, line + new_lines - 1);
-        if (parser)
-          parser->insert(line, line + new_lines - 1);
+        ctx.marks.insert(name, line, new_lines);
+        if (edit)
+          edit->insert(line, new_lines);
       }
+      ctx.current() = {name, line + new_lines};
     }
   );
-  if (parser)
-    parser->end_edit(root);
-  ctx.prev().buffername = name;
+  if (edit)
+    edit->commit(root);
   state = Modified;
 }
-
-vase::Shard *GenericBuffer::copy(uint64_t start_line, uint64_t end_line) {
-  return vase::copy(root, start_line, end_line);
-}
-
-uint64_t GenericBuffer::find_next(std::string_view pattern, uint64_t start) {
-  return vase::find_next(root, pattern, start);
-}
-
-uint64_t GenericBuffer::find_prev(std::string_view pattern, uint64_t start) {
-  return vase::find_prev(root, pattern, start);
-}
-
-uint64_t GenericBuffer::next_closing(uint64_t start) {
-  if (parser.has_value()) {
-    uint64_t closing = parser->next_closing(start - 1);
-    if (closing == UINT64_MAX)
-      return lines();
-    return closing + 1;
-  } else {
-    start += 10;
-    if (start > lines())
-      return lines();
-    return start;
-  }
-}
-
-uint64_t GenericBuffer::prev_closing(uint64_t start) {
-  if (parser.has_value()) {
-    return parser->prev_opening(start - 1) + 1;
-  } else {
-    if (start > 10)
-      return start - 10;
-    return 0;
-  }
-}
-
-inline void apply(io::IO &io, const Highlight &hl) {
-  io.write("\x1b[0m");
-  const uint8_t r = (hl.fg >> 16) & 0xff;
-  const uint8_t g = (hl.fg >> 8) & 0xff;
-  const uint8_t b = hl.fg & 0xff;
-  io.write(std::format("\x1b[38;2;{};{};{}m", r, g, b));
-  if (hl.bg != 0) {
-    const uint8_t br = (hl.bg >> 16) & 0xff;
-    const uint8_t bg = (hl.bg >> 8) & 0xff;
-    const uint8_t bb = hl.bg & 0xff;
-    io.write(std::format("\x1b[48;2;{};{};{}m", br, bg, bb));
-  }
-  if (hl.flags & Highlight::Bold)
-    io.write("\x1b[1m");
-  if (hl.flags & Highlight::Italic)
-    io.write("\x1b[3m");
-  if (hl.flags & Highlight::Underline)
-    io.write("\x1b[4m");
-  if (hl.flags & Highlight::Strikethrough)
-    io.write("\x1b[9m");
-}
-
-inline void reset(io::IO &io) {
-  io.write("\x1b[0m");
-}
-
-void GenericBuffer::print(BEd &ctx, uint64_t start_line, uint64_t end_line) {
-  ctx.prev().buffername = name;
-  ctx.prev().start = start_line;
-  ctx.prev().end = end_line;
-  if (parser) {
-    auto it_o = parser->get_hl(root, start_line - 1);
-    auto &it = *it_o;
-    while (start_line <= end_line) {
-      it.next();
-      const std::string &line = it.it->line;
-      const auto &tokens = it.tokens;
-      uint32_t cursor = 0;
-      for (const auto &token : tokens) {
-        const uint32_t start = token.start;
-        const uint32_t end = token.end;
-        if (start > line.size() || end > line.size())
-          break;
-        if (cursor < start)
-          ctx.io.write(line.data() + cursor, start - cursor);
-        const auto highlight = ctx.theme.get(token);
-        apply(ctx.io, highlight);
-        ctx.io.write(line.data() + start, end - start);
-        reset(ctx.io);
-        cursor = end;
-      }
-      if (cursor < line.size())
-        ctx.io.write(line.data() + cursor, line.size() - cursor);
-      ctx.io.write_line("");
-      ++start_line;
-    }
-  } else {
-    vase::Iterator it(root, start_line - 1, Direction::Forward);
-    while (it.next() && start_line++ <= end_line)
-      ctx.io.write_line(it.line);
-  }
-}
-
-void GenericBuffer::number_print(BEd &ctx, uint64_t start_line, uint64_t end_line) {
-  ctx.prev().buffername = name;
-  ctx.prev().start = start_line;
-  ctx.prev().end = end_line;
-  uint8_t width = 1;
-  for (uint64_t n = end_line; n >= 10; n /= 10)
-    ++width;
-  if (parser) {
-    std::optional<syntax::Parser::Iterator> it_o = parser->get_hl(root, start_line - 1);
-    auto &it = *it_o;
-    while (start_line <= end_line) {
-      it.next();
-      ctx.io.write(std::format("{:>{}}\t", start_line, width));
-      const std::string &line = it.it->line;
-      const auto &tokens = it.tokens;
-      uint32_t cursor = 0;
-      for (const auto &token : tokens) {
-        const uint32_t start = token.start;
-        const uint32_t end = token.end;
-        if (start > line.size() || end > line.size())
-          break;
-        if (cursor < start)
-          ctx.io.write(line.data() + cursor, start - cursor);
-        const auto highlight = ctx.theme.get(token);
-        apply(ctx.io, highlight);
-        ctx.io.write(line.data() + start, end - start);
-        reset(ctx.io);
-        cursor = end;
-      }
-      if (cursor < line.size())
-        ctx.io.write(line.data() + cursor, line.size() - cursor);
-      ctx.io.write_line("");
-      ++start_line;
-    }
-  } else {
-    vase::Iterator it(root, start_line - 1, Direction::Forward);
-    while (it.next() && start_line <= end_line)
-      ctx.io.write_line(std::format("{:>{}}\t{}", start_line++, width, it.line));
-  }
-}
-
-void GenericBuffer::list_print(BEd &ctx, uint64_t start_line, uint64_t end_line) {
-  ctx.prev().buffername = name;
-  ctx.prev().start = start_line;
-  ctx.prev().end = end_line;
-  vase::Iterator it(root, start_line - 1, Direction::Forward);
-  while (it.next() && start_line++ <= end_line)
-    ctx.io.write_line(list_string(it.line));
-}
 } // namespace bed::internal::buffer

src/internal/buffer/shard.cc

@@ -0,0 +1,141 @@
+#include "bed.h"
+#include "internal/buffer/buffer.h"
+
+namespace bed::internal::buffer {
+uint64_t ShardBuffer::lines() {
+  if (root)
+    return root->lines + 1;
+  return 0;
+}
+
+uint64_t ShardBuffer::bytes() {
+  if (root)
+    return root->length + 1;
+  return 0;
+}
+
+vase::Shard *ShardBuffer::copy(uint64_t start_line, uint64_t end_line) {
+  return vase::copy(root, start_line, end_line);
+}
+
+uint64_t ShardBuffer::find_next(std::string_view pattern, uint64_t start) {
+  return vase::find_next(root, pattern, start);
+}
+
+uint64_t ShardBuffer::find_prev(std::string_view pattern, uint64_t start) {
+  return vase::find_prev(root, pattern, start);
+}
+
+uint64_t ShardBuffer::next_closing(uint64_t start) {
+  if (parse.lang) {
+    uint64_t closing = syntax::next_closing(parse, start - 1);
+    return closing + 1;
+  } else {
+    start += 10;
+    if (start > lines())
+      return lines();
+    return start;
+  }
+}
+
+uint64_t ShardBuffer::prev_closing(uint64_t start) {
+  if (parse.lang) {
+    return syntax::prev_opening(parse, start - 1) + 1;
+  } else {
+    if (start > 10)
+      return start - 10;
+    return 0;
+  }
+}
+
+void ShardBuffer::print(BEd &ctx, uint64_t start_line, uint64_t end_line) {
+  ctx.prev().buffername = name;
+  ctx.prev().start = start_line;
+  ctx.prev().end = end_line;
+  if (parse.lang) {
+    auto it_o = syntax::get_hl(parse, root, start_line - 1);
+    if (!it_o)
+      goto h;
+    auto &it = *it_o;
+    while (start_line <= end_line) {
+      it.next();
+      const std::string &line = it.it->line;
+      const auto &tokens = it.tokens;
+      uint32_t cursor = 0;
+      for (const auto &token : tokens) {
+        const uint32_t start = token.start;
+        const uint32_t end = token.end;
+        if (start > line.size() || end > line.size())
+          break;
+        if (cursor < start)
+          ctx.io.write(line.data() + cursor, start - cursor);
+        ctx.io.apply(token.type);
+        ctx.io.write(line.data() + start, end - start);
+        ctx.io.reset();
+        cursor = end;
+      }
+      if (cursor < line.size())
+        ctx.io.write(line.data() + cursor, line.size() - cursor);
+      ctx.io.write_line("");
+      ++start_line;
+    }
+  } else {
+  h:
+    vase::Iterator it(root, start_line - 1, Direction::Forward);
+    while (it.next() && start_line++ <= end_line)
+      ctx.io.write_line(it.line);
+  }
+}
+
+void ShardBuffer::number_print(BEd &ctx, uint64_t start_line, uint64_t end_line) {
+  ctx.prev().buffername = name;
+  ctx.prev().start = start_line;
+  ctx.prev().end = end_line;
+  uint8_t width = 1;
+  for (uint64_t n = end_line; n >= 10; n /= 10)
+    ++width;
+  if (parse.lang) {
+    std::optional<syntax::Iterator> it_o = syntax::get_hl(parse, root, start_line - 1);
+    if (!it_o)
+      goto h;
+    auto &it = *it_o;
+    while (start_line <= end_line) {
+      it.next();
+      ctx.io.write(std::format("{:>{}}\t", start_line, width));
+      const std::string &line = it.it->line;
+      const auto &tokens = it.tokens;
+      uint32_t cursor = 0;
+      for (const auto &token : tokens) {
+        const uint32_t start = token.start;
+        const uint32_t end = token.end;
+        if (start > line.size() || end > line.size())
+          break;
+        if (cursor < start)
+          ctx.io.write(line.data() + cursor, start - cursor);
+        ctx.io.apply(token.type);
+        ctx.io.write(line.data() + start, end - start);
+        ctx.io.reset();
+        cursor = end;
+      }
+      if (cursor < line.size())
+        ctx.io.write(line.data() + cursor, line.size() - cursor);
+      ctx.io.write_line("");
+      ++start_line;
+    }
+  } else {
+  h:
+    vase::Iterator it(root, start_line - 1, Direction::Forward);
+    while (it.next() && start_line <= end_line)
+      ctx.io.write_line(std::format("{:>{}}\t{}", start_line++, width, it.line));
+  }
+}
+
+void ShardBuffer::list_print(BEd &ctx, uint64_t start_line, uint64_t end_line) {
+  ctx.prev().buffername = name;
+  ctx.prev().start = start_line;
+  ctx.prev().end = end_line;
+  vase::Iterator it(root, start_line - 1, Direction::Forward);
+  while (it.next() && start_line++ <= end_line)
+    ctx.io.write_line(list_string(it.line));
+}
+} // namespace bed::internal::buffer

src/internal/buffer/special/clip.cc

@@ -54,12 +54,12 @@ std::filesystem::path ClipBuffer::filename() {
 void ClipBuffer::append(BEd &ctx, vase::Shard *text, uint64_t line) {
   ctx.prev().buffername = name;
   ctx.prev().start = line + 1;
-  ctx.prev().end = line + text->lines + 1;
+  ctx.prev().end = line + (text ? text->lines + 1 : 0);
   auto s = vase::Shard::from_command("xclip -selection clipboard -o", true);
   s = vase::insert(&ctx.append, s, text, line);
   clip_write(s);
   vase::Shard::release(s);
-  ctx.marks.insert(name, ctx.prev().start, ctx.prev().end);
+  ctx.marks.insert(name, line, text->lines + 1);
 }
 
 void ClipBuffer::remove(BEd &ctx, uint64_t start_line, uint64_t end_line) {
@@ -73,6 +73,30 @@ void ClipBuffer::remove(BEd &ctx, uint64_t start_line, uint64_t end_line) {
   ctx.marks.erase(name, start_line, end_line - start_line + 1);
 }
 
+void ClipBuffer::replace(BEd &ctx, vase::Shard *text, uint64_t start_line, uint64_t end_line) {
+  if (!text) {
+    remove(ctx, start_line, end_line);
+    return;
+  }
+  ctx.prev().buffername = name;
+  ctx.prev().start = start_line;
+  ctx.prev().end = start_line + text->lines;
+  uint64_t new_count = text->lines + 1;
+  uint64_t old_count = end_line - start_line + 1;
+  auto s = vase::Shard::from_command("xclip -selection clipboard -o", true);
+  s = vase::replace(s, text, start_line, end_line);
+  clip_write(s);
+  vase::Shard::release(s);
+  if (new_count > old_count) {
+    uint64_t diff = new_count - old_count;
+    ctx.marks.insert(name, end_line, diff);
+  } else if (new_count < old_count) {
+    uint64_t diff = old_count - new_count;
+    ctx.marks.collapse(name, start_line + new_count - 1, diff);
+  }
+  state = Modified;
+}
+
 void ClipBuffer::join(BEd &ctx, uint64_t start_line, uint64_t end_line) {
   auto s = vase::Shard::from_command("xclip -selection clipboard -o", true);
   s = vase::join(s, start_line, end_line);
@@ -104,7 +128,7 @@ void ClipBuffer::substitute(
       if (old_lines)
         ctx.marks.erase(name, line, old_lines);
       if (new_lines)
-        ctx.marks.insert(name, line, line + new_lines - 1);
+        ctx.marks.insert(name, line, new_lines);
     }
   );
   clip_write(s);

src/internal/functions/extended.cc

@@ -3,18 +3,278 @@
 #include "internal/functions/suffixes.h"
 
 namespace bed::internal::functions {
+static std::string_view address_kind_str(Function::AddressKind k) {
+  switch (k) {
+  case Function::AddressKind::None:
+    return "none";
+  case Function::AddressKind::Line:
+    return "1 line";
+  case Function::AddressKind::Range:
+    return "range";
+  }
+  return "";
+}
+
+static std::string_view input_mode_str(Function::InputMode m) {
+  switch (m) {
+  case Function::InputMode::None:
+    return "";
+  case Function::InputMode::Text:
+    return "text";
+  case Function::InputMode::Interactive:
+    return "interactive";
+  case Function::InputMode::CommandList:
+    return "command list";
+  }
+  return "";
+}
+
+static std::string_view argument_kind_str(Function::ArgumentKind a) {
+  switch (a) {
+  case Function::ArgumentKind::None:
+    return "";
+  case Function::ArgumentKind::Regex:
+    return "regex";
+  case Function::ArgumentKind::Shell:
+    return "shell command";
+  case Function::ArgumentKind::Any:
+    return "any";
+  case Function::ArgumentKind::File:
+    return "file";
+  case Function::ArgumentKind::Global:
+    return "ed global-style";
+  case Function::ArgumentKind::Mark:
+    return "mark name";
+  case Function::ArgumentKind::Number:
+    return "number";
+  case Function::ArgumentKind::Line:
+    return "address";
+  case Function::ArgumentKind::Range:
+    return "range";
+  case Function::ArgumentKind::Ruby:
+    return "ruby code";
+  }
+  return "";
+}
+
+static void append_field(BEd &ctx, std::string_view label, io::Token::Kind color, std::string_view value) {
+  if (value.empty())
+    return;
+  ctx.io.write("\n");
+  ctx.io.apply(color);
+  ctx.io.write(label);
+  ctx.io.reset();
+  ctx.io.write(": ");
+  ctx.io.write(value);
+}
+
+static void describe_function(BEd &ctx, const Function &func) {
+  ctx.io.write(func.desc);
+  ctx.io.reset();
+  append_field(ctx, "Default address", io::Token::Color1, func.default_address);
+  append_field(ctx, "Address", io::Token::Color2, address_kind_str(func.address_kind));
+  if (func.accept_zero)
+    append_field(ctx, "Zero address", io::Token::Color3, "allowed");
+  append_field(ctx, "Input", io::Token::Color4, input_mode_str(func.input_mode));
+  append_field(ctx, "Argument", io::Token::Color5, argument_kind_str(func.argument_kind));
+  ctx.io.write("\n");
+}
+
 void Function::register_extented(BEd &ctx) {
+  ctx.functions.insert(
+    "*",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::Any,
+      .input_mode = Function::InputMode::None,
+      .desc = "Explain a command",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
+        auto str = std::get<std::string>(arg_);
+        const auto first = str.find_first_not_of(" \t");
+        const auto last = str.find_last_not_of(" \t");
+        if (first == std::string::npos)
+          str.clear();
+        else
+          str = str.substr(first, last - first + 1);
+        if (str.empty()) {
+          describe_function(ctx, ctx.no_op);
+          return;
+        }
+        auto len = ctx.functions.longest_match(str);
+        if (len == str.size()) {
+          describe_function(ctx, *ctx.functions.get_ptr(str));
+          return;
+        }
+        throw ed_error("Not a valid function name.");
+      },
+    }
+  );
+  ctx.functions.insert(
+    "b",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::None,
+      .input_mode = Function::InputMode::None,
+      .desc = "List active buffers",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &current = std::get<std::string>(addr_);
+        bool current_real = false;
+        for (auto &[name, _] : ctx.buffers) {
+          if (current == name) {
+            ctx.io.write("* ");
+            current_real = true;
+          } else {
+            ctx.io.write("  ");
+          }
+          ctx.io.write_line(name);
+        }
+        if (!current_real)
+          ctx.io.write_line("* " + current);
+      },
+    }
+  );
+  ctx.functions.insert(
+    "#",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::Any,
+      .input_mode = Function::InputMode::None,
+      .desc = "Write a comment",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {},
+    }
+  );
+  ctx.functions.insert(
+    "`",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::Ruby,
+      .input_mode = Function::InputMode::None,
+      .desc = "Execute some ruby code",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
+        // TODO: connect up to mruby.
+      },
+    }
+  );
+  ctx.functions.insert(
+    "echo",
+    Function{
+      .address_kind = Function::AddressKind::Range,
+      .argument_kind = Function::ArgumentKind::Any,
+      .input_mode = Function::InputMode::None,
+      .desc = "Echo the given message (replacing $1-$4 with address information)",
+      .default_address = "",
+      .accept_zero = true,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &addr = std::get<buffer::Range>(addr_);
+        auto str = std::get<std::string>(arg_);
+        const auto first = str.find_first_not_of(" \t");
+        const auto last = str.find_last_not_of(" \t");
+        if (first == std::string::npos)
+          str.clear();
+        else
+          str = str.substr(first, last - first + 1);
+        for (size_t i = 0; i < str.size();) {
+          if (str[i] == '\\') {
+            if (i + 1 >= str.size())
+              break;
+            str.erase(i++, 1);
+            if (str[i - 1] == 'n')
+              str[i - 1] = '\n';
+            continue;
+          }
+          if (str[i] == '$' && i < str.size() && '1' <= str[i + 1] && str[i + 1] <= '4') {
+            char c = str[i + 1];
+            str.erase(i, 2);
+            switch (c) {
+            case '1': {
+              auto start = std::to_string(addr.start);
+              str.insert(i, start);
+              i += start.size();
+            } break;
+            case '2': {
+              auto end = std::to_string(addr.end);
+              str.insert(i, end);
+              i += end.size();
+            } break;
+            case '3': {
+              str.insert(i, addr.buffername);
+              i += addr.buffername.size();
+            } break;
+            case '4': {
+              auto &buf = ctx.buffer(addr.buffername);
+              auto filename = buf.filename().string();
+              str.insert(i, filename);
+              i += filename.size();
+            } break;
+            }
+            continue;
+          }
+          i++;
+        }
+        ctx.io.write_line(str);
+      },
+    }
+  );
   ctx.functions.insert(
     "cd",
     Function{
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::Any,
       .input_mode = Function::InputMode::None,
-      .desc = "Change directory.",
+      .desc = "Change directory",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &, const buffer::Address &, vase::Shard *, const Argument &arg_, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
         auto path = std::get<std::string>(arg_);
         const auto first = path.find_first_not_of(" \t");
         const auto last = path.find_last_not_of(" \t");
@@ -42,11 +302,17 @@ void Function::register_extented(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Print directory.",
+      .desc = "Print the current working directory",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         char cwd[PATH_MAX];
         if (!getcwd(cwd, sizeof(cwd)))
           throw ed_error("Can't determine current directory.");
@@ -54,5 +320,117 @@ void Function::register_extented(BEd &ctx) {
       },
     }
   );
+  ctx.functions.insert(
+    "x",
+    Function{
+      .address_kind = Function::AddressKind::Range,
+      .argument_kind = Function::ArgumentKind::Range,
+      .input_mode = Function::InputMode::None,
+      .desc = "Exchange a range of lines for another",
+      .default_address = ".,.",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
+        auto addr = std::get<buffer::Range>(addr_);
+        auto arg = std::get<buffer::Range>(arg_);
+        auto text = ctx.buffer(addr.buffername).copy(addr.start, addr.end);
+        try {
+          ctx.buffer(arg.buffername).replace(ctx, text, arg.start, arg.end);
+          vase::Shard::release(text);
+        } catch (...) {
+          vase::Shard::release(text);
+          throw;
+        }
+      },
+    }
+  );
+  ctx.functions.insert(
+    "U",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::None,
+      .input_mode = Function::InputMode::None,
+      .desc = "Redo the last undo modification",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &addr = std::get<std::string>(addr_);
+        auto &buf_ = ctx.buffer(addr);
+        if (buf_.kind != buffer::Buffer::Kind::Generic)
+          throw ed_error("Can't redo buffer");
+        auto &buf = *(buffer::GenericBuffer *)&buf_;
+        if (!buf.redo(ctx))
+          throw ed_error("Can't redo buffer.");
+      }
+    }
+  );
+  ctx.functions.insert(
+    "hl",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::None,
+      .input_mode = Function::InputMode::None,
+      .desc = "List available history versions",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &addr = std::get<std::string>(addr_);
+        auto &buf_ = ctx.buffer(addr);
+        if (buf_.kind != buffer::Buffer::Kind::Generic)
+          throw ed_error("Can't redo buffer");
+        auto &buf = *(buffer::GenericBuffer *)&buf_;
+        buf.list_history(ctx);
+      }
+    }
+  );
+  ctx.functions.insert(
+    "hp",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::Number,
+      .input_mode = Function::InputMode::None,
+      .desc = "Prune old history versions",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &addr = std::get<std::string>(addr_);
+        auto &arg = std::get<int64_t>(arg_);
+        auto &buf_ = ctx.buffer(addr);
+        if (buf_.kind != buffer::Buffer::Kind::Generic)
+          throw ed_error("Can't prune buffer.");
+        auto &buf = *(buffer::GenericBuffer *)&buf_;
+        auto versions = buf.prune(arg);
+        if (!ctx.suppress_mode)
+          ctx.io.write_line(std::format("{} undo versions left.", versions));
+      }
+    }
+  );
 }
 } // namespace bed::internal::functions

src/internal/functions/posix.cc

@@ -34,14 +34,19 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Line,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::Text,
-      .desc = "Append text to a line.",
+      .desc = "Append text to a line",
       .default_address = ".",
       .accept_zero = true,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *text, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *text,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Line>(addr_);
         ctx.buffer(addr.buffername).append(ctx, text, addr.number);
-        ctx.current() = {ctx.prev().buffername, ctx.prev().end};
         vase::Shard::release(text);
       }
     }
@@ -52,15 +57,19 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::Text,
-      .desc = "Change set of lines.",
+      .desc = "Change a range of lines",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *text, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *text,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
-        ctx.buffer(addr.buffername).remove(ctx, addr.start, addr.end);
-        ctx.buffer(addr.buffername).append(ctx, text, addr.start - 1);
-        ctx.current() = {ctx.prev().buffername, ctx.prev().end};
+        ctx.buffer(addr.buffername).replace(ctx, text, addr.start, addr.end);
         vase::Shard::release(text);
       }
     }
@@ -71,14 +80,19 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Delete set of lines.",
+      .desc = "Delete a range of lines",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         ctx.buffer(addr.buffername).remove(ctx, addr.start, addr.end);
-        ctx.current() = {addr.buffername, addr.start};
       }
     }
   );
@@ -88,11 +102,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::File,
       .input_mode = Function::InputMode::None,
-      .desc = "Try load a file into the current buffer.",
+      .desc = "Load a file into the current buffer, warn once if unsaved changes exist",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<std::string>(addr_);
         auto &buf = ctx.buffer(addr);
         if (buf.state == buffer::Buffer::Modified) {
@@ -121,8 +141,8 @@ void Function::register_posix(BEd &ctx) {
           vase::Shard::release(s);
           throw;
         }
-        ctx.io.write_line(std::format("{}", buf.bytes()));
-        ctx.current() = {addr, buf.lines()};
+        if (!ctx.suppress_mode)
+          ctx.io.write_line(std::format("{}", buf.bytes()));
       }
     }
   );
@@ -132,11 +152,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::File,
       .input_mode = Function::InputMode::None,
-      .desc = "Load a file into the current buffer.",
+      .desc = "Load a file into the current buffer, discarding unsaved changes",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<std::string>(addr_);
         auto &buf = ctx.buffer(addr);
         vase::Shard *s = nullptr;
@@ -161,8 +187,8 @@ void Function::register_posix(BEd &ctx) {
           vase::Shard::release(s);
           throw;
         }
-        ctx.io.write_line(std::format("{}", buf.bytes()));
-        ctx.current() = {addr, buf.lines()};
+        if (!ctx.suppress_mode)
+          ctx.io.write_line(std::format("{}", buf.bytes()));
       }
     }
   );
@@ -172,16 +198,19 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::File,
       .input_mode = Function::InputMode::None,
-      .desc = "Set a save path.",
+      .desc = "Set/print a save path",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<std::string>(addr_);
-        auto &buf_ = ctx.buffer(addr);
-        if (buf_.kind != buffer::Buffer::Kind::Generic)
-          return;
-        auto &buf = *(buffer::GenericBuffer *)&buf_;
+        auto &buf = ctx.buffer(addr);
         if (std::holds_alternative<std::filesystem::path>(arg))
           buf.set_filename(std::get<std::filesystem::path>(arg));
         else if (std::holds_alternative<ShellArg>(arg))
@@ -202,8 +231,16 @@ void Function::register_posix(BEd &ctx) {
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
+        ctx.io.apply(internal::io::Token::Warning);
         ctx.io.write_line(ctx.last_help);
+        ctx.io.reset();
       }
     }
   );
@@ -213,14 +250,22 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Toggle help mode.",
+      .desc = "Toggle help mode",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         ctx.help_mode = !ctx.help_mode;
+        ctx.io.apply(internal::io::Token::Warning);
         if (ctx.help_mode)
           ctx.io.write_line(ctx.last_help);
+        ctx.io.reset();
       }
     }
   );
@@ -230,16 +275,21 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Line,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::Text,
-      .desc = "Insert text before a line.",
+      .desc = "Insert text before a line",
       .default_address = ".",
       .accept_zero = true,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *text, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *text,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Line>(addr_);
         if (addr.number)
           addr.number--;
         ctx.buffer(addr.buffername).append(ctx, text, addr.number);
-        ctx.current() = {ctx.prev().buffername, ctx.prev().end};
         vase::Shard::release(text);
       }
     }
@@ -250,14 +300,19 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Join a set of lines.",
+      .desc = "Join a range of lines",
       .default_address = ".,.+1",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         ctx.buffer(addr.buffername).join(ctx, addr.start, addr.end);
-        ctx.current() = {addr.buffername, addr.start};
       }
     }
   );
@@ -267,11 +322,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Line,
       .argument_kind = Function::ArgumentKind::Mark,
       .input_mode = Function::InputMode::None,
-      .desc = "Mark a line.",
+      .desc = "Mark a line",
       .default_address = ".",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<buffer::Line>(addr_);
         ctx.mark(std::get<char>(arg), addr);
       }
@@ -283,11 +344,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "List (print unambiguous) range",
+      .desc = "Print a range, showing nonprinting characters unambiguously",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         ctx.buffer(addr.buffername).list_print(ctx, addr.start, addr.end);
         ctx.current() = {addr.buffername, addr.end};
@@ -300,11 +367,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::Line,
       .input_mode = Function::InputMode::None,
-      .desc = "Move a range of lines.",
+      .desc = "Move a range of lines",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg_, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         auto arg = std::get<buffer::Line>(arg_);
         if (arg.buffername == addr.buffername
@@ -329,7 +402,6 @@ void Function::register_posix(BEd &ctx) {
           vase::Shard::release(text);
           throw;
         }
-        ctx.current() = {arg.buffername, arg.number + addr.end - addr.start + 1};
       },
     }
   );
@@ -339,11 +411,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Print range with line numbers",
+      .desc = "Print a range with line numbers",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         ctx.buffer(addr.buffername).number_print(ctx, addr.start, addr.end);
         ctx.current() = {addr.buffername, addr.end};
@@ -356,11 +434,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Print range",
+      .desc = "Print a range",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         ctx.buffer(addr.buffername).print(ctx, addr.start, addr.end);
         ctx.current() = {addr.buffername, addr.end};
@@ -371,17 +455,28 @@ void Function::register_posix(BEd &ctx) {
     "P",
     Function{
       .address_kind = Function::AddressKind::None,
-      .argument_kind = Function::ArgumentKind::None,
+      .argument_kind = Function::ArgumentKind::Any,
       .input_mode = Function::InputMode::None,
-      .desc = "Toggle prompt.",
+      .desc = "Toggle/set prompt string",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
-        ctx.prompt_mode = !ctx.prompt_mode;
-        if (ctx.prompt_mode && !ctx.prompt) {
-          ctx.prompt = [](BEd &) { return "*"; };
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &arg = std::get<std::string>(arg_);
+        if (arg.size()) {
+          ctx.prompt_mode = true;
+          ctx.prompt = [arg](BEd &) { return arg; };
+          return;
         }
+        ctx.prompt_mode = !ctx.prompt_mode;
+        if (ctx.prompt_mode && !ctx.prompt)
+          ctx.prompt = [](BEd &) { return "*"; };
       }
     }
   );
@@ -391,11 +486,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Try quitting.",
+      .desc = "Quit, warn once if unsaved changes exist",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         std::string modified_buffers;
         for (auto &[name, buffer] : ctx.buffers) {
           if (buffer->state == buffer::Buffer::Modified) {
@@ -416,11 +517,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Force quit.",
+      .desc = "Quit without saving, discarding unsaved changes",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &,
+                  const buffer::Address &,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         throw fatal_error("Force Quitting", 0);
       }
     }
@@ -431,11 +538,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Line,
       .argument_kind = Function::ArgumentKind::File,
       .input_mode = Function::InputMode::None,
-      .desc = "Read from file into buffer.",
+      .desc = "Read a file's contents into the buffer after the given address",
       .default_address = "$",
       .accept_zero = true,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<buffer::Line>(addr_);
         auto &buf = ctx.buffer(addr.buffername);
         vase::Shard *s = nullptr;
@@ -456,13 +569,13 @@ void Function::register_posix(BEd &ctx) {
         };
         try {
           buf.append(ctx, s, addr.number);
-          ctx.io.write_line(std::format("{}", s ? s->length + 1 : 0));
-          ctx.current() = {addr.buffername, addr.number + (s ? s->lines + 1 : 0)};
           vase::Shard::release(s);
         } catch (...) {
           vase::Shard::release(s);
           throw;
         }
+        if (!ctx.suppress_mode)
+          ctx.io.write_line(std::format("{}", s ? s->length + 1 : 0));
       }
     }
   );
@@ -472,11 +585,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::Regex,
       .input_mode = Function::InputMode::None,
-      .desc = "Substitute regex.",
+      .desc = "Substitute pattern in range for replacement",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg_, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<buffer::Range>(addr_);
         auto arg = std::get<RegexArg>(arg_);
         if (arg.expression == "")
@@ -505,11 +624,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::Line,
       .input_mode = Function::InputMode::None,
-      .desc = "Copy a range of lines.",
+      .desc = "Copy a range of lines",
       .default_address = ".,.",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg_, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         auto arg = std::get<buffer::Line>(arg_);
         auto text = ctx.buffer(addr.buffername).copy(addr.start, addr.end);
@@ -517,29 +642,56 @@ void Function::register_posix(BEd &ctx) {
           ctx.buffer(arg.buffername).append(ctx, text, arg.number);
           vase::Shard::release(text);
         } catch (...) {
-          if (!addr.start) {
-            vase::Shard::release(text);
-            throw;
-          }
-          ctx.buffer(addr.buffername).append(ctx, text, --addr.start);
           vase::Shard::release(text);
           throw;
         }
-        ctx.current() = {arg.buffername, arg.number + addr.end - addr.start + 1};
       },
     }
   );
+  ctx.functions.insert(
+    "u",
+    Function{
+      .address_kind = Function::AddressKind::None,
+      .argument_kind = Function::ArgumentKind::None,
+      .input_mode = Function::InputMode::None,
+      .desc = "Undo the last modification to the buffer",
+      .default_address = "",
+      .accept_zero = false,
+      .pre_text_mode = nullptr,
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
+        auto &addr = std::get<std::string>(addr_);
+        auto &buf_ = ctx.buffer(addr);
+        if (buf_.kind != buffer::Buffer::Kind::Generic)
+          throw ed_error("Can't undo buffer");
+        auto &buf = *(buffer::GenericBuffer *)&buf_;
+        if (!buf.undo(ctx))
+          throw ed_error("Can't undo buffer.");
+      }
+    }
+  );
   ctx.functions.insert(
     "w",
     Function{
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::File,
       .input_mode = Function::InputMode::None,
-      .desc = "Write buffer to disk.",
+      .desc = "Write a range of lines to disk",
       .default_address = "0,$",
       .accept_zero = true,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg,
+                  std::vector<buffer::Line> *
+                ) {
         auto addr = std::get<buffer::Range>(addr_);
         auto &buf = ctx.buffer(addr.buffername);
         vase::Shard *text;
@@ -565,12 +717,13 @@ void Function::register_posix(BEd &ctx) {
               throw ed_error("Need filename.");
             vase::write_file(path, text);
           };
-          ctx.io.write(std::format("{}\n", text ? text->length + 1 : 0));
           vase::Shard::release(text);
         } catch (...) {
           vase::Shard::release(text);
           throw;
         }
+        if (!ctx.suppress_mode)
+          ctx.io.write(std::format("{}\n", text ? text->length + 1 : 0));
       }
     }
   );
@@ -580,16 +733,34 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::Range,
       .argument_kind = Function::ArgumentKind::None,
       .input_mode = Function::InputMode::None,
-      .desc = "Print line numbers",
+      .desc = "Print the line number of the given address",
       .default_address = "$",
       .accept_zero = true,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<buffer::Range>(addr_);
-        if (addr.start == addr.end)
-          ctx.io.write_line(std::format(":{}:{}", addr.buffername, addr.start));
-        else
-          ctx.io.write_line(std::format(":{}:{},{}", addr.buffername, addr.start, addr.end));
+        ctx.io.apply(io::Token::BufferName);
+        ctx.io.write(":" + addr.buffername + ":");
+        ctx.io.apply(io::Token::Number);
+        if (addr.start == addr.end) {
+          ctx.io.write_line(std::format(" {}", addr.start));
+        } else {
+          ctx.io.write(std::format(" {}", addr.start));
+          ctx.io.apply(io::Token::AddressSeperator);
+          ctx.io.write(",");
+          ctx.io.apply(io::Token::Number);
+          ctx.io.write_line(std::format("{}", addr.end));
+        }
+        ctx.io.reset();
+        ctx.prev().buffername = addr.buffername;
+        ctx.prev().start = addr.start;
+        ctx.prev().end = addr.end;
         ctx.current() = {addr.buffername, addr.end};
       },
     }
@@ -600,11 +771,17 @@ void Function::register_posix(BEd &ctx) {
       .address_kind = Function::AddressKind::None,
       .argument_kind = Function::ArgumentKind::Shell,
       .input_mode = Function::InputMode::None,
-      .desc = "Run a shell command.",
+      .desc = "Run a shell command",
       .default_address = "",
       .accept_zero = false,
       .pre_text_mode = nullptr,
-      .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &arg_, std::vector<buffer::Line> *) {
+      .handle = [](
+                  BEd &ctx,
+                  const buffer::Address &addr_,
+                  vase::Shard *,
+                  const Argument &arg_,
+                  std::vector<buffer::Line> *
+                ) {
         auto &addr = std::get<std::string>(addr_);
         auto filename = ctx.buffer(addr).filename();
         auto &arg = std::get<ShellArg>(arg_);
@@ -612,7 +789,8 @@ void Function::register_posix(BEd &ctx) {
         if (ctx.escape_command(cmd, filename.string()))
           ctx.io.write(cmd + "\n");
         ctx.io.run_pty(cmd);
-        ctx.io.write("!\n");
+        if (!ctx.suppress_mode)
+          ctx.io.write("!\n");
       },
     }
   );
@@ -620,26 +798,41 @@ void Function::register_posix(BEd &ctx) {
     .address_kind = Function::AddressKind::Line,
     .argument_kind = Function::ArgumentKind::None,
     .input_mode = Function::InputMode::None,
-    .desc = "Prints a line and jumps to it.",
+    .desc = "Print given line and move the cursor to it",
     .default_address = ".+1",
     .accept_zero = true,
     .pre_text_mode = nullptr,
-    .handle = [](BEd &ctx, const buffer::Address &addr_, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+    .handle = [](
+                BEd &ctx,
+                const buffer::Address &addr_,
+                vase::Shard *,
+                const Argument &,
+                std::vector<buffer::Line> *
+              ) {
       auto addr = std::get<buffer::Line>(addr_);
       if (addr.number != 0)
         ctx.buffer(addr.buffername).print(ctx, addr.number, addr.number);
       ctx.current() = addr;
+      ctx.prev().buffername = addr.buffername;
+      ctx.prev().start = addr.number;
+      ctx.prev().end = addr.number;
     }
   };
   ctx.eof_op = Function{
     .address_kind = Function::AddressKind::None,
     .argument_kind = Function::ArgumentKind::None,
     .input_mode = Function::InputMode::None,
-    .desc = "Try quitting.",
+    .desc = "Quit, warn once if unsaved changes exist",
     .default_address = "",
     .accept_zero = false,
     .pre_text_mode = nullptr,
-    .handle = [](BEd &ctx, const buffer::Address &, vase::Shard *, const Argument &, std::vector<buffer::Line> *) {
+    .handle = [](
+                BEd &ctx,
+                const buffer::Address &,
+                vase::Shard *,
+                const Argument &,
+                std::vector<buffer::Line> *
+              ) {
       std::string modified_buffers;
       for (auto &[name, buffer] : ctx.buffers) {
         if (buffer->state == buffer::Buffer::Modified) {

src/internal/io/input.cc

@@ -1,6 +1,31 @@
 #include "internal/io/io.h"
 
 namespace bed::internal::io {
+std::pair<std::string, bool> IO::read_pipe() {
+  char buf[4096];
+  while (true) {
+    auto pos = pipe_input.find('\n');
+    if (pos != std::string::npos) {
+      std::string line = pipe_input.substr(0, pos);
+      pipe_input.erase(0, pos + 1);
+      return {line, false};
+    }
+    ssize_t n = read(STDIN_FILENO, buf, sizeof(buf));
+    if (n > 0) {
+      pipe_input.append(buf, n);
+      continue;
+    }
+    if (n == 0) {
+      std::string line = std::move(pipe_input);
+      pipe_input.clear();
+      return {line, true};
+    }
+    if (errno == EINTR)
+      continue;
+    throw fatal_error("Can't read stdin.", 1);
+  }
+}
+
 KeyEvent::ReadResult IO::get_next_byte(char &out) {
   if (!input_queue.empty()) {
     out = input_queue.front();

src/internal/io/io.cc

@@ -1,12 +1,17 @@
 #include "internal/io/io.h"
+#include "bed.h"
 
 namespace bed::internal::io {
 termios IO::orig_termios{};
 termios IO::raw_termios{};
 bool IO::cleaned = true;
 volatile std::atomic_bool IO::resized(false);
+IO::Mode IO::mode = IO::Mode::PIPE;
 
-IO::IO() {
+IO::IO(BEd &bed) : bed(bed) {
+  if (!isatty(STDIN_FILENO))
+    return;
+  mode = Mode::TERMINAL;
   if (tcgetattr(STDIN_FILENO, &orig_termios) == -1)
     throw fatal_error("Can't get terminal state.", 1);
   struct sigaction sa{};
@@ -29,17 +34,54 @@ IO::~IO() {
   cleanup();
 }
 
+void IO::apply(const io::Token::Kind &t) {
+  if (bed.suppress_mode)
+    return;
+  write("\x1b[0m");
+  const auto &hl = bed.theme.get(t);
+  const uint8_t r = (hl.fg >> 16) & 0xff;
+  const uint8_t g = (hl.fg >> 8) & 0xff;
+  const uint8_t b = hl.fg & 0xff;
+  write(std::format("\x1b[38;2;{};{};{}m", r, g, b));
+  if (hl.bg != 0) {
+    const uint8_t br = (hl.bg >> 16) & 0xff;
+    const uint8_t bg = (hl.bg >> 8) & 0xff;
+    const uint8_t bb = hl.bg & 0xff;
+    write(std::format("\x1b[48;2;{};{};{}m", br, bg, bb));
+  }
+  if (hl.flags & Highlight::Bold)
+    write("\x1b[1m");
+  if (hl.flags & Highlight::Italic)
+    write("\x1b[3m");
+  if (hl.flags & Highlight::Underline)
+    write("\x1b[4m");
+  if (hl.flags & Highlight::Strikethrough)
+    write("\x1b[9m");
+}
+
+void IO::reset() {
+  if (bed.suppress_mode)
+    return;
+  write("\x1b[0m");
+}
+
 void IO::enable_mouse() {
+  if (mode == Mode::PIPE)
+    throw fatal_error("no mouse in pipe mode.", 1);
   const char *seq = "\x1b[?1000h";
   write_all(STDOUT_FILENO, seq, 8);
 }
 
 void IO::disable_mouse() {
+  if (mode == Mode::PIPE)
+    throw fatal_error("no mouse in pipe mode.", 1);
   const char *seq = "\x1b[?1000l";
   write_all(STDOUT_FILENO, seq, 8);
 }
 
 std::pair<uint16_t, uint16_t> IO::terminal_size() {
+  if (mode == Mode::PIPE)
+    throw fatal_error("no terminal size in pipe mode.", 1);
   struct winsize ws{};
   if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1)
     throw fatal_error("Can't get terminal size.", 1);
@@ -47,6 +89,8 @@ std::pair<uint16_t, uint16_t> IO::terminal_size() {
 }
 
 std::pair<uint16_t, uint16_t> IO::cursor_position() {
+  if (mode == Mode::PIPE)
+    throw fatal_error("no cursor in pipe mode.", 1);
   write_all(STDOUT_FILENO, "\x1b[6n", 4);
   std::string response;
   char c;
@@ -69,7 +113,7 @@ std::pair<uint16_t, uint16_t> IO::cursor_position() {
 }
 
 void IO::enable_raw() {
-  if (!cleaned)
+  if (!cleaned || mode == Mode::PIPE)
     return;
   std::string os = "\x1b[?2004h";
   write_all(STDOUT_FILENO, os.c_str(), os.size());
@@ -79,7 +123,7 @@ void IO::enable_raw() {
 }
 
 void IO::cleanup() {
-  if (cleaned)
+  if (cleaned || mode == Mode::PIPE)
     return;
   std::string os = "\x1b[?1000l\x1b[?2004l";
   write_all(STDOUT_FILENO, os.c_str(), os.size());
@@ -93,6 +137,8 @@ void IO::handle_sigwinch(int) {
 }
 
 void IO::move_cursor(uint16_t row, uint16_t col) {
+  if (mode == Mode::PIPE)
+    return;
   char buf[32];
   int n = snprintf(buf, sizeof(buf), "\x1b[%u;%uH", row, col);
   write_all(STDOUT_FILENO, buf, n);
@@ -112,6 +158,8 @@ void IO::write_line(std::string_view s) {
 }
 
 void IO::run_pty(const std::string &cmd) {
+  if (mode == Mode::PIPE)
+    throw ed_error("Shell running not allowed in pipe mode.");
   int master_fd = -1;
   struct winsize ws{};
   if (ioctl(STDOUT_FILENO, TIOCGWINSZ, &ws) == -1)

src/internal/parser/address.cc

@@ -6,34 +6,74 @@ void Parser::locator(AddressPromise &addr) {
   addr.base = AddressPromise::None{};
   switch (peek()) {
   case '.':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Current{};
     break;
   case '$':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Last{};
     break;
   case '%':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::LastRange{};
     break;
   case '[':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Block{Direction::Backward};
     break;
   case ']':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Block{Direction::Forward};
     break;
   case '^':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Diagnostic{Direction::Backward};
     break;
   case '~':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Diagnostic{Direction::Forward};
     break;
   case '\'':
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)2,
+       .type = io::Token::Mark}
+    );
     advance();
     if (('a' <= peek() && peek() <= 'z')
         || ('A' <= peek() && peek() <= 'Z'))
@@ -43,6 +83,11 @@ void Parser::locator(AddressPromise &addr) {
     advance();
     break;
   case '{': {
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     uint16_t j = 0;
     std::string func;
@@ -64,8 +109,24 @@ void Parser::locator(AddressPromise &addr) {
       arg = peek_str(j);
     else
       func = peek_str(j);
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)func.size(),
+       .type = io::Token::RubyFunction}
+    );
+    if (arg.size())
+      tokens->push_back(
+        {.start = i + (uint64_t)func.size() + 1,
+         .end = i + (uint64_t)func.size() + 1 + (uint64_t)arg.size(),
+         .type = io::Token::RubyFunction}
+      );
     addr.base = AddressPromise::Scripted{std::move(func), std::move(arg)};
     advance(j + 1);
+    tokens->push_back(
+      {.start = i,
+       .end = i - (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
   } break;
   case '/': {
     advance();
@@ -87,9 +148,19 @@ void Parser::locator(AddressPromise &addr) {
       Direction::Forward,
       std::string(peek_str(j))
     );
+    tokens->push_back(
+      {.start = (uint64_t)i - 1,
+       .end = (uint64_t)i + j + 1,
+       .type = io::Token::Regexp}
+    );
     advance(j + 1);
   } break;
   case '?': {
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     uint16_t j = 0;
     while (true) {
@@ -109,6 +180,11 @@ void Parser::locator(AddressPromise &addr) {
       Direction::Backward,
       std::string(peek_str(j))
     );
+    tokens->push_back(
+      {.start = (uint64_t)i - 1,
+       .end = (uint64_t)i + j + 1,
+       .type = io::Token::Regexp}
+    );
     advance(j + 1);
   } break;
   case '<': {
@@ -132,6 +208,11 @@ void Parser::locator(AddressPromise &addr) {
       };
       break;
     }
+    tokens->push_back(
+      {.start = (uint64_t)i - 1,
+       .end = (uint64_t)i + j + 1,
+       .type = io::Token::AddressSymbol}
+    );
     advance(j + 1);
   } break;
   case '>': {
@@ -149,9 +230,19 @@ void Parser::locator(AddressPromise &addr) {
       };
       break;
     }
+    tokens->push_back(
+      {.start = (uint64_t)i - 1,
+       .end = (uint64_t)i + j + 1,
+       .type = io::Token::AddressSymbol}
+    );
     advance(j + 1);
   } break;
   case '+': {
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Current{};
     uint16_t j = 0;
@@ -162,10 +253,20 @@ void Parser::locator(AddressPromise &addr) {
     }
     if (j == 0)
       num = 1;
+    tokens->push_back(
+      {.start = (uint64_t)i,
+       .end = (uint64_t)i + j,
+       .type = io::Token::Number}
+    );
     advance(j);
     addr.offset += num;
   } break;
   case '-': {
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSymbol}
+    );
     advance();
     addr.base = AddressPromise::Current{};
     uint16_t j = 0;
@@ -176,17 +277,28 @@ void Parser::locator(AddressPromise &addr) {
     }
     if (j == 0)
       num = 1;
+    tokens->push_back(
+      {.start = (uint64_t)i,
+       .end = (uint64_t)i + j,
+       .type = io::Token::Number}
+    );
     advance(j);
     addr.offset -= num;
   } break;
   default:
     if ('0' <= peek() && peek() <= '9') {
+      uint16_t start = i;
       uint64_t num = 0;
       while ('0' <= peek() && peek() <= '9') {
         num = num * 10 + (peek() - '0');
         advance();
       }
       addr.base = AddressPromise::Number{num};
+      tokens->push_back(
+        {.start = (uint64_t)start,
+         .end = (uint64_t)i,
+         .type = io::Token::Number}
+      );
     }
   }
 }
@@ -196,14 +308,25 @@ int64_t Parser::offset() {
   while (peek() == '+' || peek() == '-'
          || ('0' <= peek() && peek() <= '9')) {
     bool positive = peek() != '-';
-    if (peek() == '+' || peek() == '-')
+    if (peek() == '+' || peek() == '-') {
+      tokens->push_back(
+        {.start = i,
+         .end = i + (uint64_t)1,
+         .type = io::Token::AddressSymbol}
+      );
       advance();
+    }
     uint16_t j = 0;
     int64_t num = 0;
     while ('0' <= peek(j) && peek(j) <= '9')
       num = num * 10 + (peek(j++) - '0');
     if (j == 0)
       num = 1;
+    tokens->push_back(
+      {.start = (uint64_t)i,
+       .end = (uint64_t)i + j,
+       .type = io::Token::Number}
+    );
     advance(j);
     offset += positive ? num : -num;
     skip_ws();
@@ -214,6 +337,7 @@ int64_t Parser::offset() {
 
 void Parser::address(AddressPromise &addr) {
   if (peek() == ':') {
+    uint16_t start = i;
     advance();
     uint16_t j = 0;
     while (peek(j) != ':' && peek(j) != '\0')
@@ -222,6 +346,11 @@ void Parser::address(AddressPromise &addr) {
     advance(j);
     if (peek() == ':')
       advance();
+    tokens->push_back(
+      {.start = start,
+       .end = i,
+       .type = io::Token::BufferName}
+    );
   }
   skip_ws();
   if (peek() == '\0')
@@ -238,6 +367,11 @@ void Parser::addresses(std::vector<AddressPromise> &addresses) {
   address(*addr);
   while (peek() == ',' || peek() == ';') {
     addr->jumping = peek() == ';';
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::AddressSeperator}
+    );
     advance();
     skip_ws();
     addresses.push_back({});

src/internal/parser/operation.cc

@@ -11,6 +11,11 @@ void Parser::operation() {
   if (len == 0)
     throw ed_error("Function not found.");
   functions::Function *function = bed.functions.get_ptr(peek_str(len));
+  tokens->push_back(
+    {.start = i,
+     .end = i + len,
+     .type = io::Token::Function}
+  );
   advance(len);
   command->function = function;
   char suffix = '\0';
@@ -27,10 +32,20 @@ void Parser::operation() {
       command->argument = peek();
     else
       throw ed_error("Valid mark needed.");
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::Mark}
+    );
     advance();
     break;
   case functions::Function::ArgumentKind::Any:
     command->argument = std::string(peek_str());
+    tokens->push_back(
+      {.start = i,
+       .end = i + peek_str().size(),
+       .type = io::Token::Any}
+    );
     advance(peek_str().size());
     break;
   case functions::Function::ArgumentKind::Global: {
@@ -108,8 +123,18 @@ void Parser::operation() {
     skip_ws();
     switch (peek()) {
     case '!':
+      tokens->push_back(
+        {.start = i,
+         .end = (uint64_t)i + 1,
+         .type = io::Token::Error}
+      );
       advance();
       command->argument = functions::Function::ShellArg(std::string(peek_str()));
+      tokens->push_back(
+        {.start = i,
+         .end = i + peek_str().size(),
+         .type = io::Token::Shell}
+      );
       advance(peek_str().size());
       break;
     case '\0':
@@ -117,6 +142,11 @@ void Parser::operation() {
       break;
     default:
       command->argument = std::filesystem::path(peek_str());
+      tokens->push_back(
+        {.start = i,
+         .end = i + peek_str().size(),
+         .type = io::Token::File}
+      );
       advance(peek_str().size());
       break;
     }
@@ -133,6 +163,7 @@ void Parser::operation() {
     char delim = peek();
     if (delim == '\0')
       throw ed_error("regex expected");
+    uint16_t start = i;
     advance();
     uint16_t j = 0;
     while (true) {
@@ -165,14 +196,25 @@ void Parser::operation() {
         j++;
     }
     std::string replacement(peek_str(j));
+    std::string options;
     if (peek(j) != '\0') {
       advance(j + 1);
     } else {
       advance(j);
+      options = "p";
     }
-    std::string options;
+    tokens->push_back(
+      {.start = start,
+       .end = i,
+       .type = io::Token::Regexp}
+    );
     if (peek() != '\0') {
       options = std::string(peek_str());
+      tokens->push_back(
+        {.start = i,
+         .end = i + peek_str().size(),
+         .type = io::Token::Suffix}
+      );
       advance(peek_str().size());
     }
     std::erase_if(options, [&](char c) {
@@ -184,17 +226,38 @@ void Parser::operation() {
     });
     command->argument = functions::Function::RegexArg(expression, replacement, options);
   } break;
-  case functions::Function::ArgumentKind::Ruby:
+  case functions::Function::ArgumentKind::Ruby: {
     command->argument = functions::Function::RubyArg(std::string(peek_str()));
+    auto *ruby_parser = bed.languages["ruby"];
+    void *state = ruby_parser->none_state();
+    std::vector<syntax::ParseEvent> events;
+    std::vector<io::Token> tokens_;
+    ruby_parser->parse(&state, peek_str(), false, &tokens_, &events);
+    for (auto &token : tokens_) {
+      token.start += i;
+      token.end += i;
+      tokens->push_back(token);
+    }
+    ruby_parser->destroy(state);
     advance(peek_str().size());
-    break;
+  } break;
   case functions::Function::ArgumentKind::Shell:
     command->argument = functions::Function::ShellArg(std::string(peek_str()));
+    tokens->push_back(
+      {.start = i,
+       .end = i + peek_str().size(),
+       .type = io::Token::Shell}
+    );
     advance(peek_str().size());
     break;
   }
   if (!suffix) {
     suffix = peek();
+    tokens->push_back(
+      {.start = i,
+       .end = i + (uint64_t)1,
+       .type = io::Token::Suffix}
+    );
     advance();
   }
   if (suffix) {

src/internal/parser/parser.cc

@@ -22,6 +22,11 @@ void Parser::skip_ws() {
 void Parser::parse() {
   skip_ws();
   if (peek() == '@') {
+    tokens->push_back(
+      {.start = 0,
+       .end = 1,
+       .type = io::Token::TempCurrent}
+    );
     advance();
     command->temp_address = true;
   } else {
@@ -37,14 +42,26 @@ void Parser::parse() {
 
 Parser::Parser(
   std::string_view cmd, BEd &bed, Command *command,
-  std::vector<ui::Token> *tokens, CompletionContext *completion
+  std::vector<io::Token> *tokens, CompletionContext *completion
 ) : bed(bed), cmd(cmd), command(command), tokens(tokens), completion(completion) {
   i = 0;
 }
 
+std::vector<io::Token> Parser::get_highlight(std::string_view cmd, BEd &bed) {
+  Command c;
+  std::vector<io::Token> tokens;
+  CompletionContext completion;
+  try {
+    Parser p(cmd, bed, &c, &tokens, &completion);
+    p.parse();
+  } catch (const ed_error &e) {
+  }
+  return tokens;
+}
+
 Command Parser::get_command(std::string_view cmd, BEd &bed) {
   Command c;
-  std::vector<ui::Token> tokens;
+  std::vector<io::Token> tokens;
   CompletionContext completion;
   Parser p(cmd, bed, &c, &tokens, &completion);
   p.parse();
@@ -53,7 +70,7 @@ Command Parser::get_command(std::string_view cmd, BEd &bed) {
 
 std::vector<AddressPromise> Parser::get_addresses(std::string_view cmd, BEd &bed) {
   std::vector<AddressPromise> result;
-  std::vector<ui::Token> tokens;
+  std::vector<io::Token> tokens;
   CompletionContext completion;
   Parser p(cmd, bed, nullptr, &tokens, &completion);
   p.addresses(result);

src/internal/syntax/iterator.cc

@@ -0,0 +1,54 @@
+#include "internal/syntax/parser.h"
+
+namespace bed::internal::syntax {
+Iterator::Iterator(uint64_t target, ParserSnapshot p, vase::Shard *vase)
+    : snap(p) {
+  uint64_t offset;
+  TreeCursor c = TreeCursor(*p.lang, p.root, target, &offset);
+  at = target - offset;
+  state = p.lang->copy(c.leaf->state);
+  it = vase::Iterator(vase, at, Direction::Forward);
+  while (at < target) {
+    it->next();
+    tokens.clear();
+    events.clear();
+    p.lang->parse(&state, it->line, at == 0, &tokens, &events);
+    at++;
+  }
+}
+
+Iterator::~Iterator() {
+  if (state)
+    snap.lang->destroy(state);
+  release(snap);
+}
+
+Iterator::Iterator(Iterator &&other)
+    : snap(other.snap),
+      it(std::move(other.it)),
+      state(other.state),
+      tokens(std::move(other.tokens)) {
+  other.snap = {};
+  other.state = nullptr;
+}
+
+Iterator &Iterator::operator=(Iterator &&other) {
+  if (this == &other)
+    return *this;
+  if (state)
+    snap.lang->destroy(state);
+  snap = other.snap;
+  it = std::move(other.it);
+  state = other.state;
+  tokens = std::move(other.tokens);
+  other.state = nullptr;
+  return *this;
+}
+
+void Iterator::next() {
+  it->next();
+  tokens.clear();
+  events.clear();
+  snap.lang->parse(&state, it->line, at++ == 0, &tokens, &events);
+}
+} // namespace bed::internal::syntax

src/internal/syntax/parser.cc

@@ -1,265 +1,32 @@
 #include "internal/syntax/parser.h"
 
 namespace bed::internal::syntax {
-static void destroy_tree(ParseState *node, Language &lang) {
-  if (!node)
-    return;
-  if (node->is_branch()) {
-    auto *branch = (ParseStateBranch *)node;
-    destroy_tree(branch->left, lang);
-    destroy_tree(branch->right, lang);
-    free(branch);
-  } else {
-    auto *leaf = (ParseStateLeaf *)node;
-    if (leaf->state)
-      lang.destroy(leaf->state);
-    if (leaf->blocks)
-      free(leaf->blocks);
-    free(leaf);
-  }
-}
-
-static ParseState *make_branch(ParseState *left, ParseState *right) {
-  if (!left)
-    return right;
-  if (!right)
-    return left;
-  auto *branch = (ParseStateBranch *)malloc(sizeof(ParseStateBranch));
-  branch->header = ParseState::BRANCH_BIT + left->lines() + right->lines();
-  branch->left = left;
-  branch->right = right;
-  return branch;
-}
-
-static ParseState *build_tree(std::vector<ParseStateLeaf *> &leaves, size_t begin, size_t end) {
-  const size_t count = end - begin;
-  if (count == 0)
-    return nullptr;
-  if (count == 1)
-    return leaves[begin];
-  const size_t mid = begin + count / 2;
-  ParseState *left = build_tree(leaves, begin, mid);
-  ParseState *right = build_tree(leaves, mid, end);
-  return make_branch(left, right);
-}
-
-Parser::Parser(vase::Shard *vase, uint64_t lines, Language lang)
-    : root(nullptr), lang(lang) {
-  reset(vase, lines, lang);
-}
-
-Parser::~Parser() {
-  destroy_tree(root, lang);
-}
-
-void Parser::reset(vase::Shard *vase, uint64_t lines, Language lang_) {
-  destroy_tree(root, lang);
-  root = nullptr;
+ParserSnapshot make_parser(vase::Shard *vase, uint64_t lines, Language *lang) {
+  ParserSnapshot snap{nullptr, lang};
   if (lines == 0)
-    return;
-  lang = std::move(lang_);
-  std::vector<ParseStateLeaf *> leaves;
-  leaves.reserve((lines + MAX_CHUNK - 1) / MAX_CHUNK);
-  uint64_t consumed = 0;
-  while (consumed < lines) {
-    auto *leaf = (ParseStateLeaf *)malloc(sizeof(ParseStateLeaf));
-    leaf->state = nullptr;
-    leaf->blocks = nullptr;
-    leaf->n = 0;
-    leaf->cap = 0;
-    uint64_t chunk = std::min(MAX_CHUNK, lines - consumed);
-    leaf->header = chunk;
-    consumed += chunk;
-    leaves.push_back(leaf);
-  }
-  root = build_tree(leaves, 0, leaves.size());
-  modify(vase, 0, lines);
+    return snap;
+  if (lang)
+    snap.root = ParseState::splice(*lang, nullptr, vase, 0, 0, lines);
+  return snap;
 }
 
-std::pair<ParseState *, ParseState *> Parser::split_tree(ParseState *node, uint64_t line) {
-  if (!node)
-    return {nullptr, nullptr};
-  if (line == 0)
-    return {nullptr, node};
-  if (line >= node->lines())
-    return {node, nullptr};
-  if (node->is_branch()) {
-    auto *branch = (ParseStateBranch *)node;
-    uint64_t left_lines = branch->left->lines();
-    if (line < left_lines) {
-      auto [a, b] = split_tree(branch->left, line);
-      ParseState *right = join_tree(b, branch->right);
-      free(branch);
-      return {a, right};
-    }
-    if (line == left_lines) {
-      ParseState *left = branch->left;
-      ParseState *right = branch->right;
-      free(branch);
-      return {left, right};
-    }
-    auto [a, b] = split_tree(branch->right, line - left_lines);
-    ParseState *left = join_tree(branch->left, a);
-    free(branch);
-    return {left, b};
-  } else {
-    auto *leaf = (ParseStateLeaf *)node;
-    uint64_t lines = leaf->lines();
-    auto *right = (ParseStateLeaf *)malloc(sizeof(ParseStateLeaf));
-    right->header = lines - line;
-    right->state = nullptr;
-    right->blocks = nullptr;
-    right->n = 0;
-    right->cap = 0;
-    leaf->header = line;
-    leaf->n = 0;
-    return {leaf, right};
-  }
+ParserSnapshot retain(const ParserSnapshot &snap) {
+  if (snap.root)
+    ParseState::retain(snap.root);
+  return snap;
 }
 
-ParseState *Parser::join_tree(ParseState *a, ParseState *b) {
-  // TODO: balance
-  return make_branch(a, b);
+void release(ParserSnapshot &snap) {
+  if (snap.root && snap.lang)
+    ParseState::release(*snap.lang, snap.root);
+  snap.root = nullptr;
 }
 
-void Parser::erase(vase::Shard *vase, uint64_t start, uint64_t count) {
-  begin_edit();
-  erase(start, count);
-  end_edit(vase);
-}
-
-void Parser::insert(vase::Shard *vase, uint64_t start, uint64_t count) {
-  begin_edit();
-  insert(start, count);
-  end_edit(vase);
-}
-
-void Parser::modify(vase::Shard *vase, uint64_t target, uint64_t count) {
-  if (count == 0 || !root)
-    return;
-  std::vector<Token> tokens;
-  std::vector<ParseEvent> events;
-  uint64_t offset;
-  TreeCursor c = TreeCursor(root, target, &offset);
-  uint64_t at = target - offset;
-  void *state = nullptr;
-  if (c.leaf->state) {
-    state = lang.copy(c.leaf->state);
-  } else {
-    while (!c.leaf->state) {
-      c.prev();
-      if (!c.leaf) {
-        at = 0;
-        break;
-      }
-      at -= c.leaf->lines();
-    }
-    if (c.leaf) {
-      state = lang.copy(c.leaf->state);
-    } else {
-      state = lang.none_state();
-      c = TreeCursor(root, 0, &offset);
-    }
-  }
-  vase::Iterator it(vase, at, Direction::Forward);
-  uint64_t chunk_start = at;
-  uint64_t next_boundary = at + c.leaf->lines();
-  c.leaf->n = 0;
-  while (true) {
-    it.next();
-    if (at == next_boundary) {
-      c.next();
-      if (!c.leaf)
-        break;
-      c.leaf->n = 0;
-      chunk_start = at;
-      next_boundary += c.leaf->lines();
-      if (at >= target + count
-          && c.leaf->state != nullptr
-          && lang.equal(state, c.leaf->state))
-        break;
-      if (c.leaf->state)
-        lang.destroy(c.leaf->state);
-      c.leaf->state = lang.copy(state);
-    }
-    tokens.clear();
-    events.clear();
-    lang.parse(&state, it.line, at == 0, &tokens, &events);
-    for (const auto &ev : events) {
-      if (c.leaf->n == c.leaf->cap) {
-        uint32_t cap = c.leaf->cap ? c.leaf->cap * 2 : 8;
-        c.leaf->blocks = (uint16_t *)realloc(c.leaf->blocks, cap * sizeof(uint16_t));
-        c.leaf->cap = cap;
-      }
-      c.leaf->blocks[c.leaf->n++] = ev.closing << 15 | (at - chunk_start);
-    }
-    at++;
-  }
-  lang.destroy(state);
-}
-
-void Parser::begin_edit() {
-  in_edit = true;
-}
-
-void Parser::mark_dirty(uint64_t start, uint64_t end) {
-  if (!dirty) {
-    dirty_start = start;
-    dirty_end = end;
-    dirty = true;
-  } else {
-    dirty_start = std::min(dirty_start, start);
-    dirty_end = std::max(dirty_end, end);
-  }
-}
-
-void Parser::erase(uint64_t start, uint64_t count) {
-  if (count == 0 || !root)
-    return;
-  auto [a, remaining] = split_tree(root, start);
-  auto [waste, b] = split_tree(remaining, count);
-  destroy_tree(waste, lang);
-  root = join_tree(a, b);
-  mark_dirty(start, start + 1);
-}
-
-void Parser::insert(uint64_t start, uint64_t count) {
-  if (count == 0)
-    return;
-  std::vector<ParseStateLeaf *> leaves;
-  leaves.reserve((count + MAX_CHUNK - 1) / MAX_CHUNK);
-  uint64_t consumed = 0;
-  while (consumed < count) {
-    auto *leaf = (ParseStateLeaf *)malloc(sizeof(ParseStateLeaf));
-    leaf->state = nullptr;
-    leaf->blocks = nullptr;
-    leaf->n = 0;
-    leaf->cap = 0;
-    uint64_t chunk = std::min(MAX_CHUNK, count - consumed);
-    leaf->header = chunk;
-    consumed += chunk;
-    leaves.push_back(leaf);
-  }
-  ParseState *subtree = build_tree(leaves, 0, leaves.size());
-  auto [left, right] = split_tree(root, start);
-  root = join_tree(join_tree(left, subtree), right);
-  mark_dirty(start, start + count);
-}
-
-void Parser::end_edit(vase::Shard *vase) {
-  in_edit = false;
-  if (!dirty)
-    return;
-  uint64_t count = dirty_end > dirty_start ? dirty_end - dirty_start : 1;
-  modify(vase, dirty_start, count);
-  dirty = false;
-}
-
-uint64_t Parser::next_closing(uint64_t line) {
-  if (!root)
-    return UINT64_MAX;
+uint64_t next_closing(const ParserSnapshot &snap, uint64_t line) {
+  if (!snap.root || !snap.lang)
+    return line + 10;
   uint64_t relative = 0;
-  TreeCursor c(root, line, &relative);
+  TreeCursor c(*snap.lang, snap.root, line, &relative);
   uint64_t line_offset = line - relative;
   int level = 0;
   bool first_leaf = true;
@@ -283,14 +50,14 @@ uint64_t Parser::next_closing(uint64_t line) {
     c.next();
     first_leaf = false;
   }
-  return UINT64_MAX;
+  return (snap.root->lines() - line > 10 ? line + 10 : snap.root->lines() - 1);
 }
 
-uint64_t Parser::prev_opening(uint64_t line) {
-  if (!root)
+uint64_t prev_opening(const ParserSnapshot &snap, uint64_t line) {
+  if (!snap.root || !snap.lang)
     return 0;
   uint64_t relative = 0;
-  TreeCursor c(root, line, &relative);
+  TreeCursor c(*snap.lang, snap.root, line, &relative);
   uint64_t line_offset = line - relative;
   int level = 0;
   bool first_leaf = true;
@@ -315,77 +82,66 @@ uint64_t Parser::prev_opening(uint64_t line) {
     if (c.leaf)
       line_offset -= c.leaf->lines();
   }
-  return 0;
+  return (line > 10 ? line - 10 : 0);
 }
 
-std::optional<Parser::Iterator> Parser::get_hl(vase::Shard *vase, uint64_t target) {
-  if (!root)
+std::optional<Iterator> get_hl(const ParserSnapshot &snap, vase::Shard *vase, uint64_t target) {
+  if (!snap.root || !snap.lang)
     return std::nullopt;
-  return Parser::Iterator(target, this, vase);
+  return Iterator(target, retain(snap), vase);
 }
 
-Parser::Iterator::Iterator(uint64_t target, Parser *p, vase::Shard *vase) : p(p) {
-  uint64_t offset;
-  TreeCursor c = TreeCursor(p->root, target, &offset);
-  at = target - offset;
-  if (c.leaf->state) {
-    state = p->lang.copy(c.leaf->state);
+void Edit::mark_dirty(uint64_t start, uint64_t end) {
+  if (!dirty) {
+    dirty_start = start;
+    dirty_end = end;
+    dirty = true;
   } else {
-    while (!c.leaf->state) {
-      c.prev();
-      if (!c.leaf) {
-        at = 0;
-        break;
-      }
-      at -= c.leaf->lines();
-    }
-    if (c.leaf) {
-      state = p->lang.copy(c.leaf->state);
-    } else {
-      state = p->lang.none_state();
-      c = TreeCursor(p->root, 0, &offset);
-    }
-  }
-  it = vase::Iterator(vase, at, Direction::Forward);
-  while (at < target) {
-    it->next();
-    tokens.clear();
-    events.clear();
-    p->lang.parse(&state, it->line, at == 0, &tokens, &events);
-    at++;
+    dirty_start = std::min(dirty_start, start);
+    dirty_end = std::max(dirty_end, end);
   }
 }
 
-Parser::Iterator::~Iterator() {
-  if (state)
-    p->lang.destroy(state);
+void Edit::insert(uint64_t start, uint64_t count) {
+  if (count == 0)
+    return;
+  uint64_t orig_pos = (uint64_t)((int64_t)start - edit_delta);
+  mark_dirty(orig_pos, orig_pos);
+  edit_delta += (int64_t)count;
 }
 
-Parser::Iterator::Iterator(Iterator &&other)
-    : p(other.p),
-      it(std::move(other.it)),
-      state(other.state),
-      tokens(std::move(other.tokens)) {
-  other.state = nullptr;
+void Edit::erase(uint64_t start, uint64_t count) {
+  if (count == 0 || !target->root)
+    return;
+  uint64_t orig_start = (uint64_t)((int64_t)start - edit_delta);
+  uint64_t orig_end = orig_start + count;
+  mark_dirty(orig_start, orig_end);
+  edit_delta -= (int64_t)count;
 }
 
-Parser::Iterator &Parser::Iterator::operator=(Iterator &&other) {
-  if (this == &other)
-    return *this;
-  if (state)
-    p->lang.destroy(state);
-  p = other.p;
-  it = std::move(other.it);
-  state = other.state;
-  tokens = std::move(other.tokens);
-  other.state = nullptr;
-  return *this;
+void Edit::commit(vase::Shard *vase) {
+  if (!dirty || !target->lang)
+    return;
+  uint64_t line = dirty_start;
+  uint64_t original = dirty_end - dirty_start;
+  uint64_t final = (uint64_t)((int64_t)original + edit_delta);
+  ParseState *new_root =
+    ParseState::splice(*target->lang, target->root, vase, line, original, final);
+  release(*target);
+  target->root = new_root;
+  dirty = false;
+  edit_delta = 0;
 }
 
-void Parser::Iterator::next() {
-  it->next();
-  tokens.clear();
-  events.clear();
-  p->lang.parse(&state, it->line, at++ == 0, &tokens, &events);
+void insert(ParserSnapshot &snap, vase::Shard *vase, uint64_t start, uint64_t count) {
+  Edit e(snap);
+  e.insert(start, count);
+  e.commit(vase);
+}
+
+void erase(ParserSnapshot &snap, vase::Shard *vase, uint64_t start, uint64_t count) {
+  Edit e(snap);
+  e.erase(start, count);
+  e.commit(vase);
 }
 } // namespace bed::internal::syntax

src/internal/syntax/parser_state.cc

@@ -0,0 +1,195 @@
+#include "internal/syntax/parser.h"
+
+namespace bed::internal::syntax {
+void ParseState::retain(ParseState *n) {
+  if (n)
+    n->refs++;
+};
+
+void ParseState::release(Language &lang, ParseState *n) {
+  if (!n || --n->refs > 0)
+    return;
+  if (n->is_branch()) {
+    auto *branch = (ParseStateBranch *)n;
+    release(lang, branch->left);
+    release(lang, branch->right);
+    delete branch;
+  } else {
+    auto *leaf = (ParseStateLeaf *)n;
+    if (leaf->state)
+      lang.destroy(leaf->state);
+    if (leaf->blocks)
+      free(leaf->blocks);
+    delete leaf;
+  }
+}
+
+int height(ParseState *n) {
+  return n ? n->height : 0;
+}
+
+int balance_factor(ParseState *n) {
+  ParseStateBranch *b = (ParseStateBranch *)n;
+  return height(b->left) - height(b->right);
+}
+
+ParseState *rotate_right(Language &lang, ParseStateBranch *z) {
+  ParseStateBranch *y = (ParseStateBranch *)z->left;
+  ParseState *middle = new ParseStateBranch(y->right, z->right);
+  ParseState *out = new ParseStateBranch(y->left, middle);
+  ParseState::release(lang, middle);
+  ParseState::release(lang, z);
+  return out;
+}
+
+ParseState *rotate_left(Language &lang, ParseStateBranch *z) {
+  ParseStateBranch *y = (ParseStateBranch *)z->right;
+  ParseState *middle = new ParseStateBranch(z->left, y->left);
+  ParseState *out = new ParseStateBranch(middle, y->right);
+  ParseState::release(lang, middle);
+  ParseState::release(lang, z);
+  return out;
+}
+
+ParseState *balance(Language &lang, ParseState *node) {
+  if (!node || !node->is_branch())
+    return node;
+  ParseStateBranch *b = (ParseStateBranch *)node;
+  int bf = balance_factor(node);
+  if (bf > 1) {
+    ParseStateBranch *left = (ParseStateBranch *)b->left;
+    if (balance_factor(left) < 0) {
+      ParseState::retain(left);
+      auto new_left = rotate_left(lang, left);
+      auto rebuilt = new ParseStateBranch(new_left, b->right);
+      auto result = rotate_right(lang, (ParseStateBranch *)rebuilt);
+      ParseState::release(lang, new_left);
+      ParseState::release(lang, b);
+      return result;
+    }
+    return rotate_right(lang, b);
+  }
+  if (bf < -1) {
+    ParseStateBranch *right = (ParseStateBranch *)b->right;
+    if (balance_factor(right) > 0) {
+      ParseState::retain(right);
+      auto new_right = rotate_right(lang, right);
+      auto rebuilt = new ParseStateBranch(b->left, new_right);
+      auto result = rotate_left(lang, (ParseStateBranch *)rebuilt);
+      ParseState::release(lang, new_right);
+      ParseState::release(lang, b);
+      return result;
+    }
+    return rotate_left(lang, b);
+  }
+  return node;
+}
+
+ParseState *ParseState::build(Language &lang, ParseState **pieces, uint64_t lo, uint64_t hi) {
+  if (hi - lo == 1)
+    return pieces[lo];
+  uint64_t mid = lo + (hi - lo) / 2;
+  ParseState *left = build(lang, pieces, lo, mid);
+  ParseState *right = build(lang, pieces, mid, hi);
+  ParseState *node = concat(lang, left, right);
+  release(lang, left);
+  release(lang, right);
+  return node;
+}
+
+ParseState *ParseState::splice(
+  Language &lang, ParseState *root, vase::Shard *vase,
+  uint64_t line, uint64_t original, uint64_t final
+) {
+  if (!vase)
+    return nullptr;
+  if (!root || (line == 0 && root->lines() == original)) {
+    vase::Iterator it(vase, 0, Direction::Forward);
+    void *state = lang.none_state();
+    std::vector<io::Token> tokens;
+    std::vector<ParseEvent> events;
+    ParsePieceBuilder builder(lang, 0);
+    for (uint64_t at = 0; at < final; ++at) {
+      it.next();
+      tokens.clear();
+      events.clear();
+      lang.parse(&state, it.line, at == 0, &tokens, &events);
+      builder.add(state, at, events);
+    }
+    lang.destroy(state);
+    return builder.finish();
+  }
+  uint64_t at;
+  void *state;
+  ParseState *prefix;
+  {
+    uint64_t offset;
+    TreeCursor c = TreeCursor(lang, root, line, &offset);
+    prefix = c.prefix();
+    at = line - offset;
+    state = lang.copy(c.leaf->state);
+  }
+  vase::Iterator it(vase, at, Direction::Forward);
+  std::vector<io::Token> tokens;
+  std::vector<ParseEvent> events;
+  uint64_t end_in_tree = line + original;
+  uint64_t end_extra;
+  TreeCursor c = TreeCursor(lang, root, end_in_tree, &end_extra);
+  uint64_t end_in_vase = line + final;
+  ParsePieceBuilder builder(lang, at);
+  while (at < end_in_vase + end_extra) {
+    it.next();
+    tokens.clear();
+    events.clear();
+    lang.parse(&state, it.line, at == 0, &tokens, &events);
+    builder.add(state, at, events);
+    ++at;
+  }
+  c.next();
+  while (c.leaf) {
+    if (lang.equal(state, c.leaf->state))
+      break;
+    for (uint64_t i = 0; i < c.leaf->lines(); ++i) {
+      it.next();
+      tokens.clear();
+      events.clear();
+      lang.parse(&state, it.line, at == 0, &tokens, &events);
+      builder.add(state, at, events);
+      ++at;
+    }
+    c.next();
+  }
+  lang.destroy(state);
+  ParseState *suffix = c.suffix();
+  ParseState *new_stuff = builder.finish();
+  auto a = concat(lang, prefix, new_stuff);
+  release(lang, prefix);
+  release(lang, new_stuff);
+  auto result = concat(lang, a, suffix);
+  release(lang, a);
+  release(lang, suffix);
+  return result;
+}
+
+ParseState *ParseState::concat(Language &lang, ParseState *a, ParseState *b) {
+  if (!a)
+    return (retain(b), b);
+  if (!b)
+    return (retain(a), a);
+  if (a->height > b->height + 1) {
+    ParseStateBranch *ba = (ParseStateBranch *)a;
+    ParseState *r = concat(lang, ba->right, b);
+    ParseState *out = balance(lang, new ParseStateBranch(ba->left, r));
+    release(lang, r);
+    return out;
+  }
+  if (b->height > a->height + 1) {
+    ParseStateBranch *bb = (ParseStateBranch *)b;
+    ParseState *l = concat(lang, a, bb->left);
+    ParseState *out = balance(lang, new ParseStateBranch(l, bb->right));
+    release(lang, l);
+    return out;
+  }
+  return balance(lang, new ParseStateBranch(a, b));
+}
+} // namespace bed::internal::syntax

src/internal/syntax/ruby/parse.cc

@@ -34,12 +34,12 @@ inline uint8_t utf8_codepoint_width(unsigned char c) {
   return 1;
 }
 
-bool handle_escapes(RubyParser &p, std::vector<Token> *tokens, uint32_t &start, bool string = true) {
+bool handle_escapes(RubyParser &p, std::vector<io::Token> *tokens, uint32_t &start, bool string = true) {
   if (p.peek() == '\\') {
     if (string)
-      tokens->push_back({start, p.i, Token::String});
+      tokens->push_back({start, p.i, io::Token::String});
     else
-      tokens->push_back({start, p.i, Token::Regexp});
+      tokens->push_back({start, p.i, io::Token::Regexp});
     start = p.i;
     p.advance();
     if (p.peek() == 'x') {
@@ -95,14 +95,14 @@ bool handle_escapes(RubyParser &p, std::vector<Token> *tokens, uint32_t &start,
     } else {
       p.advance();
     }
-    tokens->push_back({start, p.i, Token::Escape});
+    tokens->push_back({start, p.i, io::Token::Escape});
     start = p.i;
     return true;
   }
   return false;
 };
 
-bool handle_heredoc(RubyParser &p, std::vector<Token> *tokens) {
+bool handle_heredoc(RubyParser &p, std::vector<io::Token> *tokens, std::vector<ParseEvent> *events) {
   uint8_t *heredocs = p.state->heredocs();
   uint32_t start = p.i;
   if (start == 0) {
@@ -114,21 +114,22 @@ bool handle_heredoc(RubyParser &p, std::vector<Token> *tokens) {
         && memcmp(p.line.data() + start, heredocs + 1, heredoc_len) == 0) {
       if (!p.dequeue_doc(heredoc_len))
         p.current().state = RubyState::RubyInternalState::NONE;
-      tokens->push_back({p.i, p.len(), Token::Annotation});
+      events->push_back(true);
+      tokens->push_back({p.i, p.len(), io::Token::Annotation});
       p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
       return true;
     }
   }
   if (!(heredocs[0] & RubyState::Heredocs::ALLOW_INTERPOLATION)) {
-    tokens->push_back({p.i, p.len(), Token::String});
+    tokens->push_back({p.i, p.len(), io::Token::String});
     return true;
   } else {
     while (p.i < p.len()) {
       if (handle_escapes(p, tokens, start))
         continue;
       if (p.peek_str(2) == "#{") {
-        tokens->push_back({start, p.i, Token::String});
-        tokens->push_back({p.i, p.i + 2, Token::Interpolation});
+        tokens->push_back({start, p.i, io::Token::String});
+        tokens->push_back({p.i, p.i + 2, io::Token::Interpolation});
         p.advance(2);
         p.push_state();
         return false;
@@ -136,20 +137,20 @@ bool handle_heredoc(RubyParser &p, std::vector<Token> *tokens) {
       p.advance();
     }
     if (p.i >= p.len())
-      tokens->push_back({start, p.len(), Token::String});
+      tokens->push_back({start, p.len(), io::Token::String});
     return true;
   }
 }
 
-void handle_string(RubyParser &p, std::vector<Token> *tokens) {
+void handle_string(RubyParser &p, std::vector<io::Token> *tokens) {
   uint32_t start = p.i;
   while (p.i < p.len()) {
     if (handle_escapes(p, tokens, start))
       continue;
     if ((p.current().flags & RubyState::RubyInternalState::ALLOW_INTERPOLATION)
         && p.peek_str(2) == "#{") {
-      tokens->push_back({start, p.i, Token::String});
-      tokens->push_back({p.i, p.i + 2, Token::Interpolation});
+      tokens->push_back({start, p.i, io::Token::String});
+      tokens->push_back({p.i, p.i + 2, io::Token::Interpolation});
       p.advance(2);
       p.push_state();
       return;
@@ -160,7 +161,7 @@ void handle_string(RubyParser &p, std::vector<Token> *tokens) {
     if (p.peek() == p.current().delim_end) {
       if (p.current().delim_start == p.current().delim_end) {
         p.advance();
-        tokens->push_back({start, p.i, Token::String});
+        tokens->push_back({start, p.i, io::Token::String});
         p.current().state = RubyState::RubyInternalState::NONE;
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
         return;
@@ -168,7 +169,7 @@ void handle_string(RubyParser &p, std::vector<Token> *tokens) {
         p.current().lit_brace_level--;
         if (p.current().lit_brace_level == 0) {
           p.advance();
-          tokens->push_back({start, p.i, Token::String});
+          tokens->push_back({start, p.i, io::Token::String});
           p.current().state = RubyState::RubyInternalState::NONE;
           p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
           return;
@@ -178,18 +179,18 @@ void handle_string(RubyParser &p, std::vector<Token> *tokens) {
     p.advance();
   }
   if (p.i >= p.len())
-    tokens->push_back({start, p.len(), Token::String});
+    tokens->push_back({start, p.len(), io::Token::String});
 }
 
-void handle_regex(RubyParser &p, std::vector<Token> *tokens) {
+void handle_regex(RubyParser &p, std::vector<io::Token> *tokens) {
   uint32_t start = p.i;
   while (p.i < p.len()) {
     if (handle_escapes(p, tokens, start, false))
       continue;
     if ((p.current().flags & RubyState::RubyInternalState::ALLOW_INTERPOLATION)
         && p.peek_str(2) == "#{") {
-      tokens->push_back({start, p.i, Token::Regexp});
-      tokens->push_back({p.i, p.i + 2, Token::Interpolation});
+      tokens->push_back({start, p.i, io::Token::Regexp});
+      tokens->push_back({p.i, p.i + 2, io::Token::Interpolation});
       p.advance(2);
       p.push_state();
       return;
@@ -200,7 +201,7 @@ void handle_regex(RubyParser &p, std::vector<Token> *tokens) {
     if (p.peek() == p.current().delim_end) {
       if (p.current().delim_start == p.current().delim_end) {
         p.advance();
-        tokens->push_back({start, p.i, Token::Regexp});
+        tokens->push_back({start, p.i, io::Token::Regexp});
         p.current().state = RubyState::RubyInternalState::NONE;
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
         return;
@@ -208,7 +209,7 @@ void handle_regex(RubyParser &p, std::vector<Token> *tokens) {
         p.current().lit_brace_level--;
         if (p.current().lit_brace_level == 0) {
           p.advance();
-          tokens->push_back({start, p.i, Token::Regexp});
+          tokens->push_back({start, p.i, io::Token::Regexp});
           p.current().state = RubyState::RubyInternalState::NONE;
           p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
           return;
@@ -218,15 +219,15 @@ void handle_regex(RubyParser &p, std::vector<Token> *tokens) {
     p.advance();
   }
   if (p.i >= p.len())
-    tokens->push_back({start, p.len(), Token::Regexp});
+    tokens->push_back({start, p.len(), io::Token::Regexp});
 }
 
-bool handle_line_markers(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseEvent> *events) {
+bool handle_line_markers(RubyParser &p, std::vector<io::Token> *tokens, std::vector<ParseEvent> *events) {
   if (p.len() == 6 && p.peek_str(6) == "=begin") {
     p.current().state = RubyState::RubyInternalState::COMMENT;
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     events->push_back(false);
-    tokens->push_back({0, p.len(), Token::Comment});
+    tokens->push_back({0, p.len(), io::Token::Comment});
     return true;
   }
   if (p.len() == 7 && p.peek_str(7) == "__END__") {
@@ -237,20 +238,20 @@ bool handle_line_markers(RubyParser &p, std::vector<Token> *tokens, std::vector<
   return false;
 }
 
-bool handle_comment(RubyParser &p, std::vector<Token> *tokens, bool first_line) {
+bool handle_comment(RubyParser &p, std::vector<io::Token> *tokens, bool first_line) {
   if (p.peek() == '#') {
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     if (first_line && p.i == 0 && p.peek(1) == '!') {
-      tokens->push_back({0, p.len(), Token::Shebang});
+      tokens->push_back({0, p.len(), io::Token::Shebang});
       return true;
     }
-    tokens->push_back({p.i, p.len(), Token::Comment});
+    tokens->push_back({p.i, p.len(), io::Token::Comment});
     return true;
   }
   return false;
 }
 
-bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseEvent> *events) {
+bool handle_syntax(RubyParser &p, std::vector<io::Token> *tokens, std::vector<ParseEvent> *events) {
   static const RubyTries tries = RubyTries();
   if (p.peek() == ' ' || p.peek() == '\t') {
     while (p.peek() == ' ' || p.peek() == '\t')
@@ -276,7 +277,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         j++;
         while (identifier_char(p.peek(j)))
           j++;
-        tokens->push_back({p.i, p.i + j, Token::Constant});
+        tokens->push_back({p.i, p.i + j, io::Token::Constant});
         p.advance(j);
         while (p.peek() == ' ' || p.peek() == '\t')
           p.advance();
@@ -298,11 +299,11 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         if (p.peek(j) == '!' || p.peek(j) == '?')
           j++;
         if ('A' <= p.peek() && p.peek() <= 'Z')
-          tokens->push_back({p.i, p.i + j, Token::Constant});
+          tokens->push_back({p.i, p.i + j, io::Token::Constant});
         else if (j == 4 && p.peek_str(4) == "self")
-          tokens->push_back({p.i, p.i + j, Token::Keyword});
+          tokens->push_back({p.i, p.i + j, io::Token::Keyword});
         else
-          tokens->push_back({p.i, p.i + j, Token::Function});
+          tokens->push_back({p.i, p.i + j, io::Token::Function});
         p.advance(j);
         while (p.peek() == ' ' || p.peek() == '\t')
           p.advance();
@@ -321,7 +322,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         j++;
         while (identifier_char(p.peek(j)))
           j++;
-        tokens->push_back({p.i, p.i + j, Token::Constant});
+        tokens->push_back({p.i, p.i + j, io::Token::Constant});
         p.advance(j);
         while (p.peek() == ' ' || p.peek() == '\t')
           p.advance();
@@ -343,7 +344,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
       indented = true;
     if (p.peek(j) == '~' || p.peek(j) == '-')
       j++;
-    tokens->push_back({p.i, p.i + j, Token::Operator});
+    tokens->push_back({p.i, p.i + j, io::Token::Operator});
     if (p.i + j >= p.len())
       return false;
     std::string delim;
@@ -366,7 +367,8 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
       return false;
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     if (!delim.empty()) {
-      tokens->push_back({s, p.i + j, Token::Annotation});
+      events->push_back(false);
+      tokens->push_back({s, p.i + j, io::Token::Annotation});
       uint8_t header = delim.size();
       if (interpolation)
         header |= RubyState::Heredocs::ALLOW_INTERPOLATION;
@@ -380,7 +382,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
     return false;
   }
   if (p.peek() == '/' && p.current().flags & RubyState::RubyInternalState::EXPECTING_EXPRESSION) {
-    tokens->push_back({p.i, p.i + 1, Token::Regexp});
+    tokens->push_back({p.i, p.i + 1, io::Token::Regexp});
     p.current().state = RubyState::RubyInternalState::REGEXP;
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     p.current().flags |= RubyState::RubyInternalState::ALLOW_INTERPOLATION;
@@ -399,7 +401,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
       if (p.peek() == '.')
         p.advance();
     }
-    tokens->push_back({start, p.i, Token::Operator});
+    tokens->push_back({start, p.i, io::Token::Operator});
     return false;
   }
   case ':': {
@@ -407,17 +409,17 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
     uint32_t start = p.i;
     p.advance();
     if (p.i >= p.len()) {
-      tokens->push_back({start, p.i, Token::Operator});
+      tokens->push_back({start, p.i, io::Token::Operator});
       p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
       return false;
     }
     if (p.peek() == ':') {
       p.advance();
-      tokens->push_back({start, p.i, Token::Operator});
+      tokens->push_back({start, p.i, io::Token::Operator});
       return false;
     }
     if (p.peek() == '\'' || p.peek() == '"') {
-      tokens->push_back({start, p.i, Token::Label});
+      tokens->push_back({start, p.i, io::Token::Label});
       p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
       return false;
     }
@@ -428,12 +430,12 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         p.advance();
       while (identifier_char(p.peek()))
         p.advance();
-      tokens->push_back({start, p.i, Token::Label});
+      tokens->push_back({start, p.i, io::Token::Label});
       return false;
     }
     uint32_t op_len = tries.operator_trie.longest_match(p.peek_str(p.len() - p.i));
     if (op_len > 0) {
-      tokens->push_back({start, p.i + op_len, Token::Label});
+      tokens->push_back({start, p.i + op_len, io::Token::Label});
       p.advance(op_len);
       return false;
     }
@@ -443,10 +445,10 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         p.advance();
       if (p.peek() == '!' || p.peek() == '?')
         p.advance();
-      tokens->push_back({start, p.i, Token::Label});
+      tokens->push_back({start, p.i, io::Token::Label});
       return false;
     }
-    tokens->push_back({start, p.i, Token::Operator});
+    tokens->push_back({start, p.i, io::Token::Operator});
     return false;
   }
   case '@': {
@@ -463,7 +465,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
       return false;
     while (identifier_char(p.peek()))
       p.advance();
-    tokens->push_back({start, p.i, Token::VariableInstance});
+    tokens->push_back({start, p.i, io::Token::VariableInstance});
     return false;
   }
   case '$': {
@@ -510,7 +512,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         return false;
       }
     }
-    tokens->push_back({start, p.i, Token::VariableGlobal});
+    tokens->push_back({start, p.i, io::Token::VariableGlobal});
     return false;
   }
   case '?': {
@@ -526,7 +528,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           p.advance();
         if (is_hex(p.peek()))
           p.advance();
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       } else if (p.peek() == 'u') {
         p.advance();
@@ -546,7 +548,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           if (is_hex(p.peek()))
             p.advance();
         }
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       } else if ('0' <= p.peek() && p.peek() <= '7') {
         p.advance();
@@ -554,7 +556,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           p.advance();
         if ('0' <= p.peek() && p.peek() <= '7')
           p.advance();
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       } else if (p.peek() == 'c') {
         p.advance();
@@ -562,7 +564,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           p.advance();
         else
           goto combination;
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       } else if (p.peek() == 'M' || p.peek() == 'C') {
         p.advance();
@@ -573,7 +575,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           else
             goto combination;
         }
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       } else if (p.peek() == 'N') {
         p.advance();
@@ -584,28 +586,28 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           if (p.peek() == '}')
             p.advance();
         }
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       } else {
         p.advance();
-        tokens->push_back({start, p.i, Token::Char});
+        tokens->push_back({start, p.i, io::Token::Char});
         return false;
       }
     } else if (p.peek() != '\0' && p.peek() != ' ' && p.peek() != '\t') {
       p.advance();
-      tokens->push_back({start, p.i, Token::Char});
+      tokens->push_back({start, p.i, io::Token::Char});
       return false;
     } else {
       p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-      tokens->push_back({start, p.i, Token::Operator});
+      tokens->push_back({start, p.i, io::Token::Operator});
       return false;
     }
   }
   case '{': {
     p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     uint8_t brace_color =
-      (uint8_t)Token::Brace1 + (p.current().brace_level % 5);
-    tokens->push_back({p.i, p.i + 1, (Token::Kind)brace_color});
+      (uint8_t)io::Token::Brace1 + (p.current().brace_level % 5);
+    tokens->push_back({p.i, p.i + 1, (io::Token::Kind)brace_color});
     p.current().brace_level++;
     p.advance();
     return false;
@@ -614,11 +616,11 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     if (!--p.current().brace_level && p.state->top > 1) {
       p.pop_state();
-      tokens->push_back({p.i, p.i + 1, Token::Interpolation});
+      tokens->push_back({p.i, p.i + 1, io::Token::Interpolation});
     } else {
       uint8_t brace_color =
-        (uint8_t)Token::Brace1 + (p.current().brace_level % 5);
-      tokens->push_back({p.i, p.i + 1, (Token::Kind)brace_color});
+        (uint8_t)io::Token::Brace1 + (p.current().brace_level % 5);
+      tokens->push_back({p.i, p.i + 1, (io::Token::Kind)brace_color});
     }
     p.advance();
     return false;
@@ -626,8 +628,8 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
   case '(': {
     p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     uint8_t brace_color =
-      (uint8_t)Token::Brace1 + (p.current().brace_level % 5);
-    tokens->push_back({p.i, p.i + 1, (Token::Kind)brace_color});
+      (uint8_t)io::Token::Brace1 + (p.current().brace_level % 5);
+    tokens->push_back({p.i, p.i + 1, (io::Token::Kind)brace_color});
     p.current().brace_level++;
     p.advance();
     return false;
@@ -636,16 +638,16 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     p.current().brace_level--;
     uint8_t brace_color =
-      (uint8_t)Token::Brace1 + (p.current().brace_level % 5);
-    tokens->push_back({p.i, p.i + 1, (Token::Kind)brace_color});
+      (uint8_t)io::Token::Brace1 + (p.current().brace_level % 5);
+    tokens->push_back({p.i, p.i + 1, (io::Token::Kind)brace_color});
     p.advance();
     return false;
   }
   case '[': {
     p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     uint8_t brace_color =
-      (uint8_t)Token::Brace1 + (p.current().brace_level % 5);
-    tokens->push_back({p.i, p.i + 1, (Token::Kind)brace_color});
+      (uint8_t)io::Token::Brace1 + (p.current().brace_level % 5);
+    tokens->push_back({p.i, p.i + 1, (io::Token::Kind)brace_color});
     p.current().brace_level++;
     p.advance();
     return false;
@@ -654,14 +656,14 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
     p.current().brace_level--;
     uint8_t brace_color =
-      (uint8_t)Token::Brace1 + (p.current().brace_level % 5);
-    tokens->push_back({p.i, p.i + 1, (Token::Kind)brace_color});
+      (uint8_t)io::Token::Brace1 + (p.current().brace_level % 5);
+    tokens->push_back({p.i, p.i + 1, (io::Token::Kind)brace_color});
     p.advance();
     return false;
   }
   case '\'': {
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-    tokens->push_back({p.i, p.i + 1, Token::String});
+    tokens->push_back({p.i, p.i + 1, io::Token::String});
     p.current().state = RubyState::RubyInternalState::STRING;
     p.current().delim_start = '\'';
     p.current().delim_end = '\'';
@@ -671,7 +673,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
   }
   case '"': {
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-    tokens->push_back({p.i, p.i + 1, Token::String});
+    tokens->push_back({p.i, p.i + 1, io::Token::String});
     p.current().state = RubyState::RubyInternalState::STRING;
     p.current().delim_start = '"';
     p.current().delim_end = '"';
@@ -681,7 +683,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
   }
   case '`': {
     p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-    tokens->push_back({p.i, p.i + 1, Token::String});
+    tokens->push_back({p.i, p.i + 1, io::Token::String});
     p.current().state = RubyState::RubyInternalState::STRING;
     p.current().delim_start = '`';
     p.current().delim_end = '`';
@@ -691,7 +693,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
   }
   case '%': {
     if (p.i + 1 >= p.len()) {
-      tokens->push_back({p.i, p.i + 1, Token::Operator});
+      tokens->push_back({p.i, p.i + 1, io::Token::Operator});
       p.advance();
       p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
       return false;
@@ -729,14 +731,14 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
       break;
     }
     if (p.i + prefix_len >= p.len()) {
-      tokens->push_back({p.i, p.i + 1, Token::Operator});
+      tokens->push_back({p.i, p.i + 1, io::Token::Operator});
       p.advance(prefix_len);
       p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
       return false;
     }
     delim_start = p.peek(prefix_len);
     if (identifier_char(delim_start) || delim_start == ' ') {
-      tokens->push_back({p.i, p.i + 1, Token::Operator});
+      tokens->push_back({p.i, p.i + 1, io::Token::Operator});
       p.advance(prefix_len);
       p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
       return false;
@@ -758,7 +760,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
       delim_end = delim_start;
       break;
     }
-    tokens->push_back({p.i, p.i + prefix_len + 1, (is_regexp ? Token::Regexp : Token::String)});
+    tokens->push_back({p.i, p.i + prefix_len + 1, (is_regexp ? io::Token::Regexp : io::Token::String)});
     p.current().state = is_regexp
                           ? RubyState::RubyInternalState::REGEXP
                           : RubyState::RubyInternalState::STRING;
@@ -860,7 +862,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           }
         }
       }
-      tokens->push_back({start, p.i, Token::Number});
+      tokens->push_back({start, p.i, io::Token::Number});
       return false;
     } else if (identifier_start_char(p.peek())) {
       uint32_t j = 1;
@@ -870,93 +872,93 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         j++;
       if (j == tries.base_keywords_trie.longest_match(p.peek_str(j))) {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Keyword});
+        tokens->push_back({p.i, p.i + j, io::Token::Keyword});
         p.advance(j);
         return false;
       } else if (j == tries.expecting_keywords_trie.longest_match(p.peek_str(j))) {
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Keyword});
+        tokens->push_back({p.i, p.i + j, io::Token::Keyword});
         p.advance(j);
         return false;
       } else if (j == tries.operator_keywords_trie.longest_match(p.peek_str(j))) {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::KeywordOperator});
+        tokens->push_back({p.i, p.i + j, io::Token::KeywordOperator});
         p.advance(j);
         return false;
       } else if (j == tries.expecting_operators_trie.longest_match(p.peek_str(j))) {
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::KeywordOperator});
+        tokens->push_back({p.i, p.i + j, io::Token::KeywordOperator});
         p.advance(j);
         return false;
       } else if (j == tries.types_trie.longest_match(p.peek_str(j))) {
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Type});
+        tokens->push_back({p.i, p.i + j, io::Token::Type});
         p.advance(j);
         return false;
       } else if (j == tries.methods_trie.longest_match(p.peek_str(j))) {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Function});
+        tokens->push_back({p.i, p.i + j, io::Token::Function});
         p.advance(j);
         return false;
       } else if (j == tries.expecting_end_keywords_trie.longest_match(p.peek_str(j))) {
         events->push_back(false);
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Keyword});
+        tokens->push_back({p.i, p.i + j, io::Token::Keyword});
         p.advance(j);
         return false;
       } else if (j == tries.conditional_keywords_trie.longest_match(p.peek_str(j))) {
         if (p.current().flags & RubyState::RubyInternalState::NEWLINE || p.op_last)
           events->push_back(false);
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Keyword});
+        tokens->push_back({p.i, p.i + j, io::Token::Keyword});
         p.advance(j);
         return false;
       } else if (j == tries.end_keywords_trie.longest_match(p.peek_str(j))) {
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
         events->push_back(false);
-        tokens->push_back({p.i, p.i + j, Token::Keyword});
+        tokens->push_back({p.i, p.i + j, io::Token::Keyword});
         p.advance(j);
         return false;
       } else if (j == tries.builtins_trie.longest_match(p.peek_str(j))) {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Constant});
+        tokens->push_back({p.i, p.i + j, io::Token::Constant});
         p.advance(j);
         return false;
       } else if (j == tries.errors_trie.longest_match(p.peek_str(j))) {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
-        tokens->push_back({p.i, p.i + j, Token::Error});
+        tokens->push_back({p.i, p.i + j, io::Token::Error});
         p.advance(j);
         return false;
       } else if ('A' <= p.peek() && p.peek() <= 'Z' && !(p.peek(j) == '!' || p.peek(j) == '?')) {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
         if (j >= 5 && p.peek_str(j).substr(j - 5) == "Error") {
-          tokens->push_back({p.i, p.i + j, Token::Error});
+          tokens->push_back({p.i, p.i + j, io::Token::Error});
           p.advance(j);
           return false;
         }
-        tokens->push_back({p.i, p.i + j, Token::Constant});
+        tokens->push_back({p.i, p.i + j, io::Token::Constant});
         p.advance(j);
         return false;
       } else {
         p.current().flags &= ~RubyState::RubyInternalState::EXPECTING_EXPRESSION;
         if (j == 4 && p.peek_str(4) == "true") {
-          tokens->push_back({p.i, p.i + j, Token::True});
+          tokens->push_back({p.i, p.i + j, io::Token::True});
           p.advance(4);
           return false;
         }
         if (j == 5 && p.peek_str(5) == "false") {
-          tokens->push_back({p.i, p.i + j, Token::False});
+          tokens->push_back({p.i, p.i + j, io::Token::False});
           p.advance(5);
           return false;
         }
         if (j == 3 && p.peek_str(3) == "end") {
           events->push_back(true);
-          tokens->push_back({p.i, p.i + j, Token::Keyword});
+          tokens->push_back({p.i, p.i + j, io::Token::Keyword});
           p.advance(3);
           return false;
         }
         if (j == 5 && p.peek_str(5) == "class") {
-          tokens->push_back({p.i, p.i + j, Token::Keyword});
+          tokens->push_back({p.i, p.i + j, io::Token::Keyword});
           p.advance(5);
           p.current().flags =
             (p.current().flags & ~RubyState::RubyInternalState::NAME_MASK)
@@ -964,7 +966,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           return false;
         }
         if (j == 6 && p.peek_str(6) == "module") {
-          tokens->push_back({p.i, p.i + j, Token::Keyword});
+          tokens->push_back({p.i, p.i + j, io::Token::Keyword});
           p.advance(6);
           p.current().flags =
             (p.current().flags & ~RubyState::RubyInternalState::NAME_MASK)
@@ -972,7 +974,7 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           return false;
         }
         if (j == 3 && p.peek_str(3) == "def") {
-          tokens->push_back({p.i, p.i + j, Token::Keyword});
+          tokens->push_back({p.i, p.i + j, io::Token::Keyword});
           p.advance(3);
           p.current().flags =
             (p.current().flags & ~RubyState::RubyInternalState::NAME_MASK)
@@ -983,17 +985,17 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
         if (p.peek(j) == ':') {
           p.advance(j);
           p.advance();
-          tokens->push_back({start, p.i, Token::Label});
+          tokens->push_back({start, p.i, io::Token::Label});
           return false;
         } else if (p.peek(j - 1) == '!' || p.peek(j - 1) == '?') {
           p.advance(j);
-          tokens->push_back({start, p.i, Token::Function});
+          tokens->push_back({start, p.i, io::Token::Function});
           return false;
         } else {
           p.advance(j);
           j = 0;
           if (p.peek(j) == '(' || p.peek(j) == '{') {
-            tokens->push_back({start, p.i, Token::Function});
+            tokens->push_back({start, p.i, io::Token::Function});
             return false;
           } else if (p.peek(j) == ' ' || p.peek(j) == '\t') {
             j++;
@@ -1031,14 +1033,14 @@ bool handle_syntax(RubyParser &p, std::vector<Token> *tokens, std::vector<ParseE
           ) {
             return false;
           }
-          tokens->push_back({start, p.i, Token::Function});
+          tokens->push_back({start, p.i, io::Token::Function});
           return false;
         }
       }
     } else {
       uint32_t op_len;
       if ((op_len = tries.operator_trie.longest_match(p.peek_str(p.len() - p.i)))) {
-        tokens->push_back({p.i, p.i + op_len, Token::Operator});
+        tokens->push_back({p.i, p.i + op_len, io::Token::Operator});
         p.advance(op_len);
         p.current().flags |= RubyState::RubyInternalState::EXPECTING_EXPRESSION;
         p.set_op_last = true;
@@ -1054,7 +1056,7 @@ void ruby_parse(
   void **v_state,
   std::string_view line,
   bool fl,
-  std::vector<Token> *tokens,
+  std::vector<io::Token> *tokens,
   std::vector<ParseEvent> *events
 ) {
   RubyParser p(v_state, line);
@@ -1064,7 +1066,7 @@ void ruby_parse(
     if (p.current().state == RubyState::RubyInternalState::END)
       return;
     if (p.current().state == RubyState::RubyInternalState::COMMENT) {
-      tokens->push_back({p.i, p.len(), Token::Comment});
+      tokens->push_back({p.i, p.len(), io::Token::Comment});
       if (p.i == 0 && p.peek_str(4) == "=end") {
         p.current().state = RubyState::RubyInternalState::NONE;
         events->push_back(true);
@@ -1073,7 +1075,7 @@ void ruby_parse(
     }
     if (!p.heredoc_start_line
         && p.current().state == RubyState::RubyInternalState::HEREDOC) {
-      if (handle_heredoc(p, tokens))
+      if (handle_heredoc(p, tokens, events))
         return;
       else
         continue;

src/internal/syntax/tree_cursor.cc

@@ -1,7 +1,19 @@
 #include "internal/syntax/decl.h"
 
 namespace bed::internal::syntax {
-TreeCursor::TreeCursor(ParseState *root, uint64_t target_line, uint64_t *relative) {
+TreeCursor::~TreeCursor() {
+  ParseState::release(lang, root);
+}
+
+TreeCursor::TreeCursor(
+  Language &lang, ParseState *root,
+  uint64_t target_line, uint64_t *relative
+) : lang(lang), root(root) {
+  if (!root) {
+    *relative = 0;
+    return;
+  }
+  ParseState::retain(root);
   ParseState *node = root;
   while (node->is_branch()) {
     auto *branch = (ParseStateBranch *)node;
@@ -63,4 +75,42 @@ void TreeCursor::prev() {
   }
   leaf = nullptr;
 }
+
+ParseState *TreeCursor::prefix() {
+  ParseState *result = nullptr;
+  for (uint8_t i = 0; i < depth; ++i) {
+    if (went_left[i])
+      continue;
+    auto *branch = stack[i];
+    ParseState *piece = branch->left;
+    if (!result) {
+      ParseState::retain(piece);
+      result = piece;
+    } else {
+      ParseState *next = ParseState::concat(lang, result, piece);
+      ParseState::release(lang, result);
+      result = next;
+    }
+  }
+  return result;
+}
+
+ParseState *TreeCursor::suffix() {
+  ParseState *result = nullptr;
+  for (uint8_t i = depth; i-- > 0;) {
+    if (!went_left[i])
+      continue;
+    auto *branch = stack[i];
+    ParseState *piece = branch->right;
+    if (!result) {
+      ParseState::retain(piece);
+      result = piece;
+    } else {
+      ParseState *next = ParseState::concat(lang, result, piece);
+      ParseState::release(lang, result);
+      result = next;
+    }
+  }
+  return result;
+}
 } // namespace bed::internal::syntax

src/internal/theme/theme.cc

@@ -5,150 +5,262 @@ Theme::Theme() {
   hl.fill({
     .fg = 0xF0F0F0,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   });
 }
 
-Highlight Theme::get(internal::syntax::Token token) const {
-  return hl[token.type];
+io::Highlight Theme::get(const io::Token::Kind &token) const {
+  return hl[token];
 }
 
 Theme Theme::default_theme() {
   Theme theme;
-  theme.hl[internal::syntax::Token::Shebang] = {
-    .fg = 0x7DCFFF,
+
+  theme.hl[io::Token::TempCurrent] = {
+    .fg = 0x7AA2F7,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Error] = {
-    .fg = 0xEF5168,
+  theme.hl[io::Token::BufferName] = {
+    .fg = 0xBB9AF7,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Comment] = {
-    .fg = 0xAAAAAA,
+  theme.hl[io::Token::AddressSeperator] = {
+    .fg = 0xA9B1D6,
     .bg = 0x000000,
-    .flags = Highlight::Italic,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::String] = {
-    .fg = 0xAAD94C,
+  theme.hl[io::Token::Address] = {
+    .fg = 0xE0AF68,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Escape] = {
-    .fg = 0x7DCFFF,
+  theme.hl[io::Token::Offset] = {
+    .fg = 0xFFAF70,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Interpolation] = {
-    .fg = 0x7DCFFF,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::Regexp] = {
+  theme.hl[io::Token::AddressRegex] = {
     .fg = 0xD2A6FF,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Number] = {
-    .fg = 0xE6C08A,
+  theme.hl[io::Token::AddressSymbol] = {
+    .fg = 0xFF9E64,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::True] = {
-    .fg = 0x7AE93C,
+  theme.hl[io::Token::Mark] = {
+    .fg = 0xFF757F,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::False] = {
-    .fg = 0xEF5168,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::Char] = {
-    .fg = 0xFFAF70,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::Keyword] = {
-    .fg = 0xFF8F40,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::KeywordOperator] = {
-    .fg = 0xF07178,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::Operator] = {
-    .fg = 0xFFFFFF,
-    .bg = 0x000000,
-    .flags = Highlight::Italic,
-  };
-  theme.hl[internal::syntax::Token::Function] = {
-    .fg = 0xFFAF70,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::Type] = {
-    .fg = 0xF07178,
-    .bg = 0x000000,
-    .flags = Highlight::None,
-  };
-  theme.hl[internal::syntax::Token::Constant] = {
+  theme.hl[io::Token::RubyFunction] = {
     .fg = 0x7DCFFF,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::VariableInstance] = {
+  theme.hl[io::Token::RubyArg] = {
+    .fg = 0xA9B1D6,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Any] = {
+    .fg = 0x7DCFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Shell] = {
+    .fg = 0x89DDFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Ruby] = {
     .fg = 0x95E6CB,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::VariableGlobal] = {
+  theme.hl[io::Token::File] = {
+    .fg = 0xAAD94C,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Replacement] = {
+    .fg = 0x9ECE6A,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Suffix] = {
     .fg = 0xF07178,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Annotation] = {
+  theme.hl[io::Token::Color1] = {
+    .fg = 0x7AA2F7,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Color2] = {
+    .fg = 0xAAD94C,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Color3] = {
+    .fg = 0xFF9E64,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Color4] = {
+    .fg = 0xBB9AF7,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Color5] = {
+    .fg = 0xFF757F,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Warning] = {
+    .fg = 0xF1C55A,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  // Data is terminal default.
+  theme.hl[io::Token::Shebang] = {
     .fg = 0x7DCFFF,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Directive] = {
+  theme.hl[io::Token::Error] = {
+    .fg = 0xEF5168,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Comment] = {
+    .fg = 0xAAAAAA,
+    .bg = 0x000000,
+    .flags = io::Highlight::Italic,
+  };
+  theme.hl[io::Token::String] = {
+    .fg = 0xAAD94C,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Escape] = {
+    .fg = 0x7DCFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Interpolation] = {
+    .fg = 0x7DCFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Regexp] = {
+    .fg = 0x7DCFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Number] = {
+    .fg = 0xE6C08A,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::True] = {
+    .fg = 0x7AE93C,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::False] = {
+    .fg = 0xEF5168,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Char] = {
+    .fg = 0xFFAF70,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Keyword] = {
     .fg = 0xFF8F40,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Label] = {
+  theme.hl[io::Token::KeywordOperator] = {
+    .fg = 0xF07178,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Operator] = {
+    .fg = 0xFFFFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::Italic,
+  };
+  theme.hl[io::Token::Function] = {
+    .fg = 0xFFAF70,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Type] = {
+    .fg = 0xF07178,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Constant] = {
+    .fg = 0x7DCFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::VariableInstance] = {
+    .fg = 0x95E6CB,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::VariableGlobal] = {
+    .fg = 0xF07178,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Annotation] = {
+    .fg = 0x7DCFFF,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Directive] = {
+    .fg = 0xFF8F40,
+    .bg = 0x000000,
+    .flags = io::Highlight::None,
+  };
+  theme.hl[io::Token::Label] = {
     .fg = 0xD2A6FF,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Brace1] = {
+  theme.hl[io::Token::Brace1] = {
     .fg = 0xD2A6FF,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Brace2] = {
+  theme.hl[io::Token::Brace2] = {
     .fg = 0xFFAFAF,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Brace3] = {
+  theme.hl[io::Token::Brace3] = {
     .fg = 0xFFFF00,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Brace4] = {
+  theme.hl[io::Token::Brace4] = {
     .fg = 0x0FFF0F,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
-  theme.hl[internal::syntax::Token::Brace5] = {
+  theme.hl[io::Token::Brace5] = {
     .fg = 0xFF0F0F,
     .bg = 0x000000,
-    .flags = Highlight::None,
+    .flags = io::Highlight::None,
   };
   return theme;
 }
@@ -156,7 +268,6 @@ Theme Theme::default_theme() {
 Theme Theme::from_name(std::string_view name) {
   if (name == "default")
     return default_theme();
-  throw std::runtime_error("Unknown theme: " + std::string(name));
+  throw ed_error("Unknown theme: " + std::string(name));
 }
-
 } // namespace bed::internal::theme

src/internal/ui/command/command.cc

@@ -1,5 +1,6 @@
 #include "internal/ui/command.h"
 #include "bed.h"
+#include "internal/parser/parser.h"
 
 namespace bed::internal::ui {
 /*template <typename F>
@@ -69,6 +70,17 @@ CommandIO::CommandIO(BEd &bed) : bed(bed) {
 }
 
 std::pair<std::string, bool> CommandIO::run() {
+  if (!bed.io.interactive())
+    return run_pipe();
+  return run_terminal();
+}
+
+std::pair<std::string, bool> CommandIO::run_pipe() {
+  bed.io.write(prompt);
+  return bed.io.read_pipe();
+}
+
+std::pair<std::string, bool> CommandIO::run_terminal() {
   auto [row, col] = bed.io.cursor_position();
   auto [rows, cols] = bed.io.terminal_size();
   if (row > rows)
@@ -151,7 +163,22 @@ void CommandIO::redraw() {
   bed.io.write("\x1b[2K", 4);
   bed.io.move_cursor(start, 1);
   bed.io.write(prompt);
-  bed.io.write(cmd);
+  const auto tokens = parser::Parser::get_highlight(cmd, bed);
+  uint32_t pos = 0;
+  for (const auto &token : tokens) {
+    const uint32_t tstart = token.start;
+    const uint32_t tend = token.end;
+    if (tstart > cmd.size())
+      break;
+    if (pos < tstart)
+      bed.io.write(cmd.data() + pos, tstart - pos);
+    bed.io.apply(token.type);
+    bed.io.write(cmd.data() + tstart, tend - tstart);
+    bed.io.reset();
+    pos = tend;
+  }
+  if (pos < cmd.size())
+    bed.io.write(cmd.data() + pos, cmd.size() - pos);
   bed.io.move_cursor(start, prompt.size() + cursor + 1);
 }
 } // namespace bed::internal::ui

src/internal/ui/text_mode/text_mode.cc

@@ -7,6 +7,23 @@ TextMode::TextMode(BEd &bed) : bed(bed) {
 }
 
 std::pair<vase::Shard *, bool> TextMode::run() {
+  if (!bed.io.interactive())
+    return run_pipe();
+  return run_terminal();
+}
+
+std::pair<vase::Shard *, bool> TextMode::run_pipe() {
+  cmd.clear();
+  while (true) {
+    auto [str, eof] = bed.io.read_pipe();
+    if (str == "." || eof)
+      break;
+    cmd += str + "\n";
+  }
+  return {vase::Shard::from_string(cmd.data(), cmd.length(), true), false};
+}
+
+std::pair<vase::Shard *, bool> TextMode::run_terminal() {
   auto [row, col] = bed.io.cursor_position();
   auto [rows, cols] = bed.io.terminal_size();
   if (row > rows)
@@ -42,9 +59,8 @@ std::pair<vase::Shard *, bool> TextMode::run() {
             cmd.erase(--cursor, 1);
           }
         } else if (res.text[0] == '\n') {
-          size_t lines = 1 + std::count(cmd.begin(), cmd.end(), '\n');
-          grow(lines + 1);
           cmd.insert(cursor++, 1, '\n');
+          grow();
         } else {
           cmd.insert(cursor, res.text);
           cursor += res.text.size();
@@ -55,6 +71,7 @@ std::pair<vase::Shard *, bool> TextMode::run() {
     case io::KeyEvent::KeyType::PASTE:
       cmd.insert(cursor, res.text);
       cursor += res.text.size();
+      grow();
       break;
     case io::KeyEvent::KeyType::SPECIAL:
       switch (res.special_key) {
@@ -123,16 +140,22 @@ std::pair<vase::Shard *, bool> TextMode::run() {
       cursor = cmd.size();
       running = false;
     }
+    if (cmd.size() == 2 && cmd.compare(0, 2, ".\n") == 0) {
+      cmd.clear();
+      cursor = 0;
+      running = false;
+    }
   }
 
-  size_t total_lines = 1 + std::count(cmd.begin(), cmd.end(), '\n');
+  size_t total_lines = cmd.size() ? 1 + std::count(cmd.begin(), cmd.end(), '\n') : 0;
   uint16_t last_row = start + total_lines;
   bed.io.move_cursor(last_row, 1);
   bed.io.write("\n", 1);
   return {vase::Shard::from_string(cmd.data(), cmd.length(), true), false};
 }
 
-void TextMode::grow(size_t required_height) {
+void TextMode::grow() {
+  size_t required_height = 1 + std::count(cmd.begin(), cmd.end(), '\n');
   auto [rows, cols] = bed.io.terminal_size();
   term_height = rows;
   term_width = cols;

src/internal/vase/regex/api.cc

@@ -90,12 +90,7 @@ Shard *substitute(
   if (matches.empty())
     return root;
   std::vector<ReplacePart> replace_parts = parse_replace(ap, replace);
-  struct Edit {
-    uint64_t line;
-    uint64_t old_lines;
-    uint64_t new_lines;
-  };
-  uint64_t orig_line = start;
+  uint64_t current_line = 1;
   int64_t line_delta = 0;
   std::vector<Shard *> pieces;
   pieces.reserve(matches.size() * 2 + 1);
@@ -109,7 +104,7 @@ Shard *substitute(
       Shard::release(remaining);
       pieces.push_back(keep);
       remaining = rest;
-      orig_line += keep ? keep->lines : 0;
+      current_line += keep ? keep->lines : 0;
     }
     auto [dropped, rest2] = Shard::split(remaining, match.end - match.start);
     Shard::release(remaining);
@@ -152,13 +147,11 @@ Shard *substitute(
       }
     }
     Shard::release(dropped);
-    if (old_lines || new_lines) {
-      uint64_t report_line = (uint64_t)((int64_t)orig_line + line_delta);
-      if (on_edit)
-        on_edit(report_line, old_lines, new_lines);
-      line_delta += (int64_t)new_lines - (int64_t)old_lines;
-    }
-    orig_line += old_lines;
+    uint64_t report_line = (uint64_t)((int64_t)current_line + line_delta);
+    if (on_edit)
+      on_edit(report_line, old_lines, new_lines);
+    line_delta += (int64_t)new_lines - (int64_t)old_lines;
+    current_line += old_lines;
     cursor = match.end;
   }
   pieces.push_back(remaining);

src/internal/vase/shard.cc

@@ -289,6 +289,8 @@ Shard *Shard::from_command(const char *cmd, bool posix_ending) {
         last = nullptr;
         if (!pieces.empty())
           last = (Petal *)pieces.back();
+        else
+          return nullptr;
       }
       if (last && ending[0] == '\r')
         last->length--;

src/internal/vase/vase.cc

@@ -173,6 +173,8 @@ Shard *insert(AppendStorage *ap, Shard *root, Shard *text, uint64_t line) {
     Shard::retain(text);
     return text;
   }
+  if (!text)
+    return root;
   if (line > root->lines + 1)
     throw ed_error("line out of range");
   Shard::retain(text);
@@ -201,6 +203,34 @@ Shard *insert(AppendStorage *ap, Shard *root, Shard *text, uint64_t line) {
   return result;
 }
 
+Shard *replace(Shard *root, Shard *text, uint64_t start, uint64_t end) {
+  if (!start || !end)
+    throw ed_error("Invalid range.");
+  start--;
+  end--;
+  if (!root)
+    throw ed_error("line range out of bounds");
+  uint64_t line_count = root->lines + 1;
+  if (start > end || end >= line_count)
+    throw ed_error("line range out of bounds");
+  uint64_t start_offset = offset_of(root, start);
+  uint64_t end_offset =
+    (end + 1 == line_count)
+      ? root->length
+      : offset_of(root, end + 1) - 1;
+  auto [left, rest] = Shard::split(root, start_offset);
+  auto [middle, right] = Shard::split(rest, end_offset - start_offset);
+  Shard *a = Shard::concat(left, text);
+  Shard *new_root = Shard::concat(a, right);
+  Shard::release(left);
+  Shard::release(rest);
+  Shard::release(middle);
+  Shard::release(right);
+  Shard::release(a);
+  Shard::release(root);
+  return new_root;
+}
+
 Shard *erase(Shard *root, uint64_t start, uint64_t end) {
   if (!start || !end)
     throw ed_error("Invalid range.");

src/main.cc

@@ -4,8 +4,7 @@
 int main(int argc, char *argv[]) {
   std::vector<std::string> args(argv, argv + argc);
   try {
-    bed::internal::io::IO io = bed::internal::io::IO();
-    bed::BEd ed(args, io);
+    bed::BEd ed(args);
     ed.run();
   } catch (bed::fatal_error &e) {
     if (e.code)