parseForExpr

    pub fn parseForExpr(p: *Parser) Error!bool {
        const def_index = @backingInt(Def.defForExpr);
        if (p.depths[def_index] > max_depth) return error.MaxDepth;
        p.depths[def_index] += 1;
        defer p.depths[def_index] -= 1;
        return blk_0: {
            const pos_0 = p.i;
            if (try p.parseForPrefix() and try p.parseExpr() and blk_2: {
                const pos_2 = p.i;
                if (try p.parseKEYWORD_else() and try p.parseExpr()) break :blk_2 true;
                p.i = pos_2;
                if (blk_3: {
                    const pos_3 = p.i;
                    const match_3 = try p.parseKEYWORD_else();
                    p.i = pos_3;
                    break :blk_3 !match_3;
                }) break :blk_2 true;
                p.i = pos_2;
                break :blk_2 false;
            }) break :blk_0 true;
            p.i = pos_0;
            break :blk_0 false;
        };
    }