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feat: if let 语句 — if let Option::Some = expr { ... }

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This commit is contained in:
刘航宇
2026-06-06 15:20:34 +08:00
parent 0e1f8c5795
commit e02cc7b1d6
4 changed files with 98 additions and 39 deletions
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src/parser/parser.c
+55 -28
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@@ -1,4 +1,5 @@
#include "parser.h"
#include <stdio.h>
#include <string.h>
#include <stdlib.h>
@@ -265,21 +266,58 @@ static AstNode* parse_expr_prec(Parser* p, Precedence min_prec, ErrorInfo* error
// 前缀解析
if (tok->kind == TOK_IF) {
// if-expr: if cond { then } else { else } → AST_IF_STMT (表达式位置)
const Token* if_tok = advance(p);
AstNode* cond = parse_expr(p, error);
if (!cond) return NULL;
AstNode* then_block = parse_block(p, error);
if (!then_block) return NULL;
AstNode* else_block = NULL;
if (match(p, TOK_ELSE)) {
if (peek(p)->kind == TOK_IF)
else_block = parse_expr_prec(p, min_prec, error); // else if
else
else_block = parse_block(p, error);
if (!else_block) return NULL;
// if let: if let Pattern = expr { then } else { else } → 去糖为 let+if
if (peek(p)->kind == TOK_LET) {
advance(p); // 跳过 let
// 解析模式: Enum::Variant 或 Enum::Variant(var)
AstNode* pattern = parse_expr(p, error); // 解析枚举变体
if (!pattern) return NULL;
if (!expect(p, TOK_ASSIGN, error, "if let 缺少 '='")) return NULL;
AstNode* match_expr = parse_expr(p, error);
if (!match_expr) return NULL;
AstNode* then_block = parse_block(p, error);
if (!then_block) return NULL;
AstNode* else_block = NULL;
if (match(p, TOK_ELSE)) {
if (peek(p)->kind == TOK_IF)
else_block = parse_expr_prec(p, min_prec, error);
else
else_block = parse_block(p, error);
if (!else_block) return NULL;
}
// 去糖: { let __match = expr; if __match == pattern { then } else { else } }
static int iflet_counter = 0;
char vname_buf[32];
snprintf(vname_buf, sizeof(vname_buf), "__iflet_%d", iflet_counter++);
const char* vname = arena_strdup_impl(p->arena, vname_buf, strlen(vname_buf));
AstNode* let_stmt = ast_make_let(p->arena,
vname, TYPE_UNKNOWN,
false, false, match_expr, NULL, 0, NULL, 0, tok_loc(if_tok));
AstNode* cond = ast_make_binary(p->arena, OP_EQ,
ast_make_ident(p->arena, vname, tok_loc(if_tok)),
pattern, tok_loc(if_tok));
AstNode* if_stmt = ast_make_if(p->arena, cond, then_block, else_block, tok_loc(if_tok));
AstNode* stmts[2] = { let_stmt, if_stmt };
AstNode** arr = arena_alloc_impl(p->arena, 2 * sizeof(AstNode*));
memcpy(arr, stmts, 2 * sizeof(AstNode*));
left = ast_make_block(p->arena, arr, 2, tok_loc(if_tok));
} else {
// if-expr: if cond { then } else { else }
AstNode* cond = parse_expr(p, error);
if (!cond) return NULL;
AstNode* then_block = parse_block(p, error);
if (!then_block) return NULL;
AstNode* else_block = NULL;
if (match(p, TOK_ELSE)) {
if (peek(p)->kind == TOK_IF)
else_block = parse_expr_prec(p, min_prec, error);
else
else_block = parse_block(p, error);
if (!else_block) return NULL;
}
left = ast_make_if(p->arena, cond, then_block, else_block, tok_loc(if_tok));
}
left = ast_make_if(p->arena, cond, then_block, else_block, tok_loc(if_tok));
} else if (tok->kind == TOK_MINUS || tok->kind == TOK_BANG) {
left = parse_unary(p, error);
} else if (tok->kind == TOK_LPAREN) {
@@ -632,21 +670,10 @@ static AstNode* parse_statement(Parser* p, ErrorInfo* error) {
}
if (t->kind == TOK_IF) {
advance(p);
AstNode* cond = parse_expr(p, error);
if (!cond) return NULL;
AstNode* then_block = parse_block(p, error);
if (!then_block) return NULL;
AstNode* else_block = NULL;
if (match(p, TOK_ELSE)) {
if (peek(p)->kind == TOK_IF) {
else_block = parse_statement(p, error);
} else {
else_block = parse_block(p, error);
}
if (!else_block) return NULL;
}
return ast_make_if(p->arena, cond, then_block, else_block, tok_loc(t));
// 委托给表达式解析器（含 if let 去糖）
AstNode* if_expr = parse_expr_prec(p, PREC_NONE, error);
if (!if_expr) return NULL;
return if_expr; // AST_IF_STMT 或 AST_BLOCK(if-let去糖)
}
if (t->kind == TOK_WHILE) {