Make substitutions work and other minor fixes.

include/internal/syntax/parser.h

@@ -10,6 +10,10 @@ struct Parser {
 
   ParseState *root;
   Language lang;
+  bool in_edit = false;
+  bool dirty = false;
+  uint64_t dirty_start = 0;
+  uint64_t dirty_end = 0;
 
   Parser(vase::Shard *, uint64_t, Language);
   ~Parser();
@@ -21,6 +25,12 @@ struct Parser {
   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);
 

include/internal/vase/vase.h

@@ -20,8 +20,8 @@ struct Range {
 };
 
 struct RegexGroup {
-  uint64_t start{0};
-  uint64_t end{0};
+  uint64_t start{UINT64_MAX};
+  uint64_t end{UINT64_MAX};
 };
 
 struct RegexMatch {
@@ -57,7 +57,10 @@ uint64_t find_prev(Shard *root, std::string_view pattern, uint64_t start);
 Shard *substitute(
   AppendStorage *ap, Shard *root,
   std::string_view pattern, uint64_t start, uint64_t end,
-  std::string_view replace, std::string_view options
+  std::string_view replace, std::string_view options,
+  const std::function<void(
+    uint64_t line, uint64_t old_lines, uint64_t new_lines
+  )> &on_edit = nullptr
 );
 
 // internal