comptime expandable match statements

tree-sitter-brolang/grammar.js

@@ -339,7 +339,7 @@ module.exports = grammar({
     ),
 
     for_statement: $ => seq(
-      optional('inline'),
+      optional('expand'),
       'for',
       repeat($._newline),
       field('iterable', $.expression),
@@ -364,16 +364,30 @@ module.exports = grammar({
       '}',
     ),
 
-    match_arm: $ => seq(
+    match_arm: $ => choice(seq(
       field('pattern', choice('else', commaSep1($, $.expression))),
       optional($.match_capture),
       ':',
       repeat($._newline),
       field('body', $._branch_body),
-    ),
+    ), seq(
+      'expand',
+      $.expand_match_capture,
+      ':',
+      repeat($._newline),
+      field('body', $._branch_body),
+    )),
 
     match_capture: $ => seq('|', optional('@'), field('name', choice($.identifier, $.sink)), '|'),
 
+    expand_match_capture: $ => seq(
+      '|',
+      optional('@'),
+      field('value', choice($.identifier, $.sink)),
+      optional(seq(',', field('tag', choice($.identifier, $.sink)))),
+      '|',
+    ),
+
     _branch_body: $ => $.statement,
 
     _value: $ => choice(