feat: for step 步长 — for i in 0 to 10 step 2 { ... }

Token(75): +TOK_STEP, desugar_for 增加 step_expr 参数, 默认 step=1

Co-Authored-By: Claude Opus 4.7 <noreply@anthropic.com>

src/lexer/lexer.c

@@ -58,7 +58,7 @@ static TokenKind check_keyword(const Token* tok) {
     KW("var",    TOK_VAR);
     KW("if",     TOK_IF);     KW("else",   TOK_ELSE);  KW("guard",  TOK_GUARD);
     KW("while",  TOK_WHILE);  KW("for",    TOK_FOR);  KW("in",     TOK_IN);
-    KW("to",     TOK_TO);
+    KW("to",     TOK_TO);    KW("step", TOK_STEP);
 	    KW("return", TOK_RETURN);
     KW("i32",    TOK_I32);    KW("i64",    TOK_I64);
     KW("u64",    TOK_U64);    KW("f64",    TOK_F64);

src/lexer/token.c

@@ -22,7 +22,7 @@ static const char* NAMES[] = {
     [TOK_EQ_EQ] = "==", [TOK_BANG_EQ] = "!=",
     [TOK_LT] = "<", [TOK_GT] = ">", [TOK_LT_EQ] = "<=", [TOK_GT_EQ] = ">=",
     [TOK_AND_AND] = "&&", [TOK_PIPE_PIPE] = "||", [TOK_PIPE] = "|>", [TOK_BANG] = "!",
-    [TOK_ARROW] = "->", [TOK_TO] = "to", [TOK_MATCH_ARROW] = "=>",
+    [TOK_ARROW] = "->", [TOK_TO] = "to", [TOK_STEP] = "step", [TOK_MATCH_ARROW] = "=>",
     [TOK_PLUS_EQ] = "+=", [TOK_MINUS_EQ] = "-=", [TOK_STAR_EQ] = "*=", [TOK_SLASH_EQ] = "/=",
     [TOK_LPAREN] = "(", [TOK_RPAREN] = ")",
     [TOK_LBRACE] = "{", [TOK_RBRACE] = "}",

src/lexer/token.h

@@ -19,7 +19,7 @@ typedef enum {
     TOK_PLUS, TOK_MINUS, TOK_STAR, TOK_SLASH, TOK_PERCENT,
     TOK_EQ_EQ, TOK_BANG_EQ, TOK_LT, TOK_GT, TOK_LT_EQ, TOK_GT_EQ,
     TOK_AND_AND, TOK_PIPE_PIPE, TOK_PIPE, TOK_BANG,
-    TOK_ARROW, TOK_TO, TOK_MATCH_ARROW,
+    TOK_ARROW, TOK_TO, TOK_STEP, TOK_MATCH_ARROW,
     TOK_PLUS_EQ, TOK_MINUS_EQ, TOK_STAR_EQ, TOK_SLASH_EQ,
     // 分隔符
     TOK_LPAREN, TOK_RPAREN, TOK_LBRACE, TOK_RBRACE,

src/parser/desugar.c

@@ -39,25 +39,23 @@ AstNode* desugar_guard(Parser* p, const Token* guard_tok,
     return ast_make_if(p->arena, not_cond, body, NULL, tok_loc(guard_tok));
 }
 
-// === for i in start to end { body } → { var i = start; while i < end { body; i = i + 1; } } ===
+// === for i in start to end [step N] { body } → { var i=start; while i<end { body; i=i+step; } } ===
 AstNode* desugar_for(Parser* p, const Token* for_tok,
                      const char* var_name, AstNode* start_expr,
-                     AstNode* end_expr, AstNode* body) {
-    // var i = start;
+                     AstNode* end_expr, AstNode* step_expr, AstNode* body) {
     AstNode* let_stmt = ast_make_let(p->arena, var_name, TYPE_UNKNOWN,
         false, true, start_expr, NULL, 0, NULL, 0, tok_loc(for_tok));
 
-    // i < end
     AstNode* cond = ast_make_binary(p->arena, OP_LT,
         ast_make_ident(p->arena, var_name, tok_loc(for_tok)),
         end_expr, tok_loc(for_tok));
 
-    // i = i + 1
+    AstNode* step = step_expr ? step_expr
+        : ast_make_literal_i64(p->arena, 1, tok_loc(for_tok));
     AstNode* incr = ast_make_assign(p->arena, var_name,
         ast_make_binary(p->arena, OP_ADD,
             ast_make_ident(p->arena, var_name, tok_loc(for_tok)),
-            ast_make_literal_i64(p->arena, 1, tok_loc(for_tok)),
-            tok_loc(for_tok)),
+            step, tok_loc(for_tok)),
         tok_loc(for_tok));
 
     // 增量追加到循环体末尾

src/parser/desugar.h

@@ -13,10 +13,10 @@ AstNode* desugar_match(Parser* p, const Token* match_tok,
 AstNode* desugar_guard(Parser* p, const Token* guard_tok,
                        AstNode* cond, AstNode* body);
 
-// for i in start to end { body } → { var i = start; while i < end { body; i = i + 1; } }
+// for i in start to end [step N] { body } → { var i=start; while i<end { body; i=i+step; } }
 AstNode* desugar_for(Parser* p, const Token* for_tok,
                      const char* var_name, AstNode* start_expr,
-                     AstNode* end_expr, AstNode* body);
+                     AstNode* end_expr, AstNode* step_expr, AstNode* body);
 
 // if let pattern = expr { then } else { else } → { let __match = expr; if __match == pattern ... }
 AstNode* desugar_if_let(Parser* p, const Token* if_tok,

src/parser/parser.c

@@ -176,10 +176,16 @@ AstNode* parse_statement(Parser* p, ErrorInfo* error) {
         if (!expect(p, TOK_TO, error, "缺少 'to'")) return NULL;
         AstNode* end_expr = parse_expr(p, error);
         if (!end_expr) return NULL;
+        AstNode* step_expr = NULL;
+        if (peek(p)->kind == TOK_STEP) {
+            advance(p);
+            step_expr = parse_expr(p, error);
+            if (!step_expr) return NULL;
+        }
         AstNode* body = parse_block(p, error);
         if (!body) return NULL;
         const char* vname = arena_strdup_impl(p->arena, var_name->start, var_name->length);
-        return desugar_for(p, t, vname, start_expr, end_expr, body);
+        return desugar_for(p, t, vname, start_expr, end_expr, step_expr, body);
     }
 
     if (t->kind == TOK_MATCH) {

test/programs/41_for_step.l

@@ -0,0 +1,6 @@
+fn main() -> i64 {
+    for i in 0 to 10 step 2 {
+        print_i64(i);
+    }
+    return 0;
+}