feat: let mut 改为 var 关键字声明可变变量

src/parser/parser.c

@@ -472,11 +472,10 @@ static AstNode* parse_block(Parser* p, ErrorInfo* error) {
 static AstNode* parse_statement(Parser* p, ErrorInfo* error) {
     const Token* t = peek(p);
 
-    if (t->kind == TOK_LET) {
-        advance(p);
-        bool is_mut = false;
-        if (peek(p)->kind == TOK_MUT) { is_mut = true; advance(p); }
-        const Token* name = expect(p, TOK_IDENT, error, "let 后应为变量名");
+    if (t->kind == TOK_LET || t->kind == TOK_VAR) {
+        bool is_mut = (advance(p)->kind == TOK_VAR);
+        const Token* name = expect(p, TOK_IDENT, error,
+            is_mut ? "var 后应为变量名" : "let 后应为变量名");
         if (!name) return NULL;
         // 可选的类型标注
         TypeKind annot_type = TYPE_UNKNOWN;
@@ -558,11 +557,11 @@ static AstNode* parse_statement(Parser* p, ErrorInfo* error) {
         if (!body) return NULL;
 
         // 脱糖: for i in start to end { body; }
-        //   → { let mut i = start; while i < end { body; i = i + 1; } }
+        //   → { var i = start; while i < end { body; i = i + 1; } }
 
         const char* vname = arena_strdup_impl(p->arena, var_name->start, var_name->length);
 
-        // 构建: let mut i = start;
+        // 构建: var i = start;
         AstNode* let_stmt = ast_make_let(p->arena, vname, TYPE_UNKNOWN, false, true, start_expr, NULL, 0, NULL, 0, tok_loc(var_name));
 
         // 构建: i < end  (while 条件)
@@ -589,7 +588,7 @@ static AstNode* parse_statement(Parser* p, ErrorInfo* error) {
         // 构建: while i < end { ... body ... ; i = i + 1; }
         AstNode* while_loop = ast_make_while(p->arena, cond, new_body, tok_loc(t));
 
-        // 包装: { let mut i = start; while i < end { ... } }
+        // 包装: { var i = start; while i < end { ... } }
         AstNode* stmts_arr[2] = { let_stmt, while_loop };
         AstNode** stmts = arena_alloc_impl(p->arena, 2 * sizeof(AstNode*));
         memcpy(stmts, stmts_arr, 2 * sizeof(AstNode*));