feat: let mut 改为 var 关键字声明可变变量

src/lexer/lexer.c

@@ -55,7 +55,7 @@ static Token lex_number(Lexer* l) {
 static TokenKind check_keyword(const Token* tok) {
     #define KW(s, k) if (tok->length == sizeof(s)-1 && memcmp(tok->start, s, sizeof(s)-1) == 0) return k
     KW("fn",     TOK_FN);     KW("let",    TOK_LET);
-    KW("mut",    TOK_MUT);
+    KW("var",    TOK_VAR);
     KW("if",     TOK_IF);     KW("else",   TOK_ELSE);
     KW("while",  TOK_WHILE);  KW("for",    TOK_FOR);  KW("in",     TOK_IN);
     KW("to",     TOK_TO);

src/lexer/token.c

@@ -5,7 +5,7 @@
 #include <inttypes.h>
 
 static const char* NAMES[] = {
-    [TOK_FN] = "fn", [TOK_LET] = "let", [TOK_MUT] = "mut", [TOK_IF] = "if",
+    [TOK_FN] = "fn", [TOK_LET] = "let", [TOK_VAR] = "var", [TOK_IF] = "if",
     [TOK_ELSE] = "else", [TOK_WHILE] = "while", [TOK_FOR] = "for", [TOK_IN] = "in", [TOK_RETURN] = "return",
     [TOK_STRUCT] = "struct", [TOK_TYPE] = "type", [TOK_ENUM] = "enum", [TOK_IMPL] = "impl",
     [TOK_MATCH] = "match",

src/lexer/token.h

@@ -6,7 +6,7 @@
 // === Token 类型枚举 ===
 typedef enum {
     // 关键字
-    TOK_FN, TOK_LET, TOK_MUT, TOK_IF, TOK_ELSE, TOK_WHILE, TOK_FOR, TOK_IN, TOK_RETURN,
+    TOK_FN, TOK_LET, TOK_VAR, TOK_IF, TOK_ELSE, TOK_WHILE, TOK_FOR, TOK_IN, TOK_RETURN,
     TOK_STRUCT, TOK_TYPE, TOK_ENUM, TOK_IMPL, TOK_MATCH,
     // 类型关键字
     TOK_I64, TOK_F64, TOK_BOOL, TOK_STR, TOK_VOID,

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*));

src/sema/sema.c

@@ -683,7 +683,7 @@ static void analyze_node(AstNode* node, Scope* scope, ErrorList* errors, Arena*
         }
         if (!sym->is_mut) {
             error_add(errors, "<sema>", node->loc.line, node->loc.col,
-                      "不能对不可变变量 '%s' 赋值（需用 let mut 声明）",
+                      "不能对不可变变量 '%s' 赋值（需用 var 声明）",
                       node->as.assign_stmt.name);
             node->type.kind = TYPE_ERROR;
             break;