add yue.format() function. fix yue ast to code function issues.

6 files changed, 276 insertions, 76 deletions

diff --git a/src/yue_wasm.cpp b/src/yue_wasm.cpp
index 4a054e6..daa5757 100644
--- a/src/yue_wasm.cpp
+++ b/src/yue_wasm.cpp
@@ -138,7 +138,7 @@ std::string exec(const std::string& codes) {
         };
 
         execStr(R"yuescript(
-_G.__output = {}
+_G.__output = []
 _G.print = (...)->
         _G.__output[] = table.concat [tostring select i, ... for i = 1, select "#", ...], " "
         _G.__output[] = "\n"
diff --git a/src/yuescript/yue_ast.cpp b/src/yuescript/yue_ast.cpp
index 6126f71..6b2c96d 100644
--- a/src/yuescript/yue_ast.cpp
+++ b/src/yuescript/yue_ast.cpp
@@ -230,7 +230,7 @@ std::string LocalValues_t::to_string(void* ud) const {
         temp.emplace_back(nameList->to_string(ud));
         if (valueList) {
                 if (valueList.is<TableBlock_t>()) {
-                        temp.emplace_back("="s + valueList->to_string(ud));
+                        temp.emplace_back("=\n"s + valueList->to_string(ud));
                 } else {
                         temp.emplace_back("="s);
                         temp.emplace_back(valueList->to_string(ud));
@@ -312,7 +312,10 @@ std::string ShortTabAppending_t::to_string(void* ud) const {
 std::string Backcall_t::to_string(void* ud) const {
         str_list temp;
         if (argsDef) {
-                temp.emplace_back(argsDef->to_string(ud));
+                auto def = argsDef->to_string(ud);
+                if (!def.empty()) {
+                        temp.emplace_back(def);
+                }
         }
         temp.emplace_back(arrow->to_string(ud));
         temp.emplace_back(value->to_string(ud));
@@ -343,7 +346,7 @@ std::string ExpList_t::to_string(void* ud) const {
 std::string Return_t::to_string(void* ud) const {
         str_list temp{"return"s};
         if (valueList) {
-                temp.emplace_back(valueList.is<TableBlock_t>() ? ""s : " "s);
+                temp.emplace_back(valueList.is<TableBlock_t>() ? "\n"s : " "s);
                 temp.emplace_back(valueList->to_string(ud));
         }
         return join(temp);
@@ -365,6 +368,9 @@ std::string With_t::to_string(void* ud) const {
                 }
                 info->pushScope();
                 auto code = body->to_string(ud);
+                if (code.empty()) {
+                        code = info->ind() + "--"s;
+                }
                 info->popScope();
                 return line + '\n' + code;
         }
@@ -383,6 +389,9 @@ std::string SwitchCase_t::to_string(void* ud) const {
         } else {
                 info->pushScope();
                 auto block = body->to_string(ud);
+                if (block.empty()) {
+                        block = info->ind() + "--"s;
+                }
                 info->popScope();
                 auto line = "when "s + condition->to_string(ud);
                 if (line.find('\n') != std::string::npos) {
@@ -405,6 +414,9 @@ std::string Switch_t::to_string(void* ud) const {
                         temp.emplace_back(info->ind() + "else"s);
                         info->pushScope();
                         temp.emplace_back(lastBranch->to_string(ud));
+                        if (temp.back().empty()) {
+                                temp.back() = info->ind() + "--"s;
+                        }
                         info->popScope();
                 }
         }
@@ -412,10 +424,18 @@ std::string Switch_t::to_string(void* ud) const {
         return join(temp, "\n"sv);
 }
 std::string Assignment_t::to_string(void* ud) const {
-        return expList->to_string(ud) + ' ' + assign->to_string(ud);
+        if (expList) {
+                return ", "s + expList->to_string(ud) + " :"s + assign->to_string(ud);
+        } else {
+                return " :"s + assign->to_string(ud);
+        }
 }
 std::string IfCond_t::to_string(void* ud) const {
-        return condition->to_string(ud);
+        if (assignment) {
+                return condition->to_string(ud) + assignment->to_string(ud);
+        } else {
+                return condition->to_string(ud);
+        }
 }
 std::string If_t::to_string(void* ud) const {
         auto info = reinterpret_cast<YueFormat*>(ud);
@@ -447,11 +467,17 @@ std::string If_t::to_string(void* ud) const {
                                 if (condition) {
                                         info->pushScope();
                                         temp.emplace_back(node->to_string(ud));
+                                        if (temp.back().empty()) {
+                                                temp.back() = info->ind() + "--"s;
+                                        }
                                         info->popScope();
                                 } else {
                                         temp.emplace_back(info->ind() + "else"s);
                                         info->pushScope();
                                         temp.emplace_back(node->to_string(ud));
+                                        if (temp.back().empty()) {
+                                                temp.back() = info->ind() + "--"s;
+                                        }
                                         info->popScope();
                                 }
                                 condition = false;
@@ -473,6 +499,9 @@ std::string While_t::to_string(void* ud) const {
                 }
                 info->pushScope();
                 temp.emplace_back(body->to_string(ud));
+                if (temp.back().empty()) {
+                        temp.back() = info->ind() + "--"s;
+                }
                 info->popScope();
         }
         return join(temp, "\n"sv);
@@ -486,6 +515,9 @@ std::string Repeat_t::to_string(void* ud) const {
                 temp.emplace_back("repeat"s);
                 info->pushScope();
                 temp.emplace_back(body->to_string(ud));
+                if (temp.back().empty()) {
+                        temp.back() = info->ind() + "--"s;
+                }
                 info->popScope();
         }
         temp.emplace_back(info->ind() + "until "s + condition->to_string(ud));
@@ -508,6 +540,9 @@ std::string For_t::to_string(void* ud) const {
                 }
                 info->pushScope();
                 auto block = body->to_string(ud);
+                if (block.empty()) {
+                        block = info->ind() + "--"s;
+                }
                 info->popScope();
                 return line + '\n' + block;
         }
@@ -523,6 +558,9 @@ std::string ForEach_t::to_string(void* ud) const {
                 }
                 info->pushScope();
                 auto block = body->to_string(ud);
+                if (block.empty()) {
+                        block = info->ind() + "--"s;
+                }
                 info->popScope();
                 return line + '\n' + block;
         }
@@ -534,6 +572,9 @@ std::string Do_t::to_string(void* ud) const {
         } else {
                 info->pushScope();
                 auto block = body->to_string(ud);
+                if (block.empty()) {
+                        block = info->ind() + "--"s;
+                }
                 info->popScope();
                 return "do\n"s + block;
         }
@@ -543,6 +584,9 @@ std::string CatchBlock_t::to_string(void* ud) const {
         auto line = "catch "s + err->to_string(ud);
         info->pushScope();
         auto block = body->to_string(ud);
+        if (block.empty()) {
+                block = info->ind() + "--"s;
+        }
         info->popScope();
         return line + '\n' + block;
 }
@@ -555,6 +599,9 @@ std::string Try_t::to_string(void* ud) const {
                 temp.emplace_back("try"s);
                 info->pushScope();
                 temp.emplace_back(func->to_string(ud));
+                if (temp.back().empty()) {
+                        temp.back() = info->ind() + "--"s;
+                }
                 info->popScope();
         }
         if (catchBlock) {
@@ -571,7 +618,11 @@ std::string Comprehension_t::to_string(void* ud) const {
                 temp.front().insert(0, temp.front()[0] == '[' ? " "s : ""s);
         }
         if (items.size() != 2 || !ast_is<CompInner_t>(items.back())) {
-                return '[' + join(temp, ", "sv) + ']';
+                if (items.size() == 1) {
+                        return '[' + join(temp, ", "sv) + ",]"s;
+                } else {
+                        return '[' + join(temp, ", "sv) + ']';
+                }
         } else {
                 return '[' + join(temp, " "sv) + ']';
         }
@@ -613,7 +664,7 @@ std::string CompInner_t::to_string(void* ud) const {
 std::string Assign_t::to_string(void* ud) const {
         str_list temp;
         if (values.size() == 1 && ast_is<TableBlock_t>(values.front())) {
-                return '=' + values.front()->to_string(ud);
+                return "=\n"s + values.front()->to_string(ud);
         }
         for (auto value : values.objects()) {
                 temp.emplace_back(value->to_string(ud));
@@ -790,7 +841,13 @@ static bool isInBlockExp(ast_node* node) {
                                         TblComprehension_t, Comprehension_t>(simpleValue->value)) {
                                 return true;
                         }
+                } else if (auto chainValue = value->item.as<ChainValue_t>()) {
+                        if (ast_is<InvokeArgs_t>(chainValue->items.back())) {
+                                return true;
+                        }
                 }
+        } else if (ast_is<TableBlock_t>(node)) {
+                return true;
         }
         return false;
 }
@@ -863,7 +920,7 @@ std::string TableBlock_t::to_string(void* ud) const {
                                 temp.emplace_back(info->ind() + "* "s + value->to_string(ud));
                                 break;
                         case id<TableBlock_t>():
-                                temp.emplace_back(info->ind() + "*"s + value->to_string(ud));
+                                temp.emplace_back(info->ind() + "*\n"s + value->to_string(ud));
                                 break;
                         default:
                                 temp.emplace_back(info->ind() + value->to_string(ud));
@@ -871,21 +928,25 @@ std::string TableBlock_t::to_string(void* ud) const {
                 }
         }
         info->popScope();
-        return '\n' + join(temp, "\n"sv);
+        return join(temp, "\n"sv);
 }
 std::string TableBlockIndent_t::to_string(void* ud) const {
         auto info = reinterpret_cast<YueFormat*>(ud);
         str_list temp;
         info->pushScope();
         for (auto value : values.objects()) {
-                if (value == values.front()) {
-                        temp.emplace_back("* "s + value->to_string(ud));
+                if (ast_is<TableBlockIndent_t>(value)) {
+                        temp.emplace_back("\n"s + value->to_string(ud));
                 } else {
-                        temp.emplace_back(info->ind() + value->to_string(ud));
+                        if (value == values.front()) {
+                                temp.emplace_back(" "s + value->to_string(ud));
+                        } else {
+                                temp.emplace_back(info->ind() + value->to_string(ud));
+                        }
                 }
         }
         info->popScope();
-        return join(temp, "\n"sv);
+        return "*"s + join(temp, "\n"sv);
 }
 std::string ClassMemberList_t::to_string(void* ud) const {
         auto info = reinterpret_cast<YueFormat*>(ud);
@@ -893,7 +954,7 @@ std::string ClassMemberList_t::to_string(void* ud) const {
         for (auto value : values.objects()) {
                 temp.emplace_back(info->ind() + value->to_string(ud));
         }
-        return join(temp, "\n"sv);
+        return join(temp, ", "sv);
 }
 std::string ClassBlock_t::to_string(void* ud) const {
         auto info = reinterpret_cast<YueFormat*>(ud);
@@ -929,7 +990,7 @@ std::string GlobalValues_t::to_string(void* ud) const {
         auto line = nameList->to_string(ud);
         if (valueList) {
                 if (valueList.is<TableBlock_t>()) {
-                        line += " ="s + valueList->to_string(ud);
+                        line += " =\n"s + valueList->to_string(ud);
                 } else {
                         line += " = "s + valueList->to_string(ud);
                 }
@@ -949,8 +1010,12 @@ std::string Export_t::to_string(void* ud) const {
                         line += target->to_string(ud);
                         break;
                 case id<Exp_t>(): {
-                        auto valueStr = target->to_string(ud);
-                        line += '[' + (valueStr[0] == '[' ? " "s : ""s) + valueStr + ']';
+                        if (def) {
+                                line += target->to_string(ud);
+                        } else {
+                                auto valueStr = target->to_string(ud);
+                                line += '[' + (valueStr[0] == '[' ? " "s : ""s) + valueStr + ']';
+                        }
                         break;
                 }
                 default:
@@ -973,7 +1038,7 @@ std::string NormalPair_t::to_string(void* ud) const {
         } else {
                 line = key->to_string(ud) + ":"s;
         }
-        line += (value.is<TableBlock_t>() ? ""s : " "s) + value->to_string(ud);
+        line += (value.is<TableBlock_t>() ? "\n"s : " "s) + value->to_string(ud);
         return line;
 }
 std::string MetaVariablePair_t::to_string(void* ud) const {
@@ -989,7 +1054,7 @@ std::string MetaNormalPair_t::to_string(void* ud) const {
         } else {
                 line = '<' + key->to_string(ud) + ">:"s;
         }
-        line += (value.is<TableBlock_t>() ? ""s : " "s) + value->to_string(ud);
+        line += (value.is<TableBlock_t>() ? "\n"s : " "s) + value->to_string(ud);
         return line;
 }
 std::string VariablePairDef_t::to_string(void* ud) const {
@@ -1033,23 +1098,38 @@ std::string FnArgDef_t::to_string(void* ud) const {
                 line += op->to_string(ud);
         }
         if (defaultValue) {
-                if (isInBlockExp(defaultValue)) {
-                        line += " = ("s + defaultValue->to_string(ud) + ')';
-                } else {
-                        line += " = "s + defaultValue->to_string(ud);
-                }
+                line += " = "s + defaultValue->to_string(ud);
         }
         return line;
 }
 std::string FnArgDefList_t::to_string(void* ud) const {
+        auto info = reinterpret_cast<YueFormat*>(ud);
         str_list temp;
+        bool hasInBlockExp = false;
         for (auto def : definitions.objects()) {
-                temp.emplace_back(def->to_string(ud));
+                auto argDef = static_cast<FnArgDef_t*>(def);
+                if (argDef->defaultValue && isInBlockExp(argDef->defaultValue)) {
+                        hasInBlockExp = true;
+                        break;
+                }
         }
-        if (varArg) {
-                temp.emplace_back(varArg->to_string(ud));
+        if (hasInBlockExp) {
+                for (auto def : definitions.objects()) {
+                        temp.emplace_back(info->ind() + def->to_string(ud));
+                }
+                if (varArg) {
+                        temp.emplace_back(info->ind() + varArg->to_string(ud));
+                }
+                return join(temp, "\n"sv);
+        } else {
+                for (auto def : definitions.objects()) {
+                        temp.emplace_back(def->to_string(ud));
+                }
+                if (varArg) {
+                        temp.emplace_back(varArg->to_string(ud));
+                }
+                return join(temp, ", "sv);
         }
-        return join(temp, ", "sv);
 }
 std::string OuterVarShadow_t::to_string(void* ud) const {
         if (varList) {
@@ -1059,14 +1139,38 @@ std::string OuterVarShadow_t::to_string(void* ud) const {
         }
 }
 std::string FnArgsDef_t::to_string(void* ud) const {
-        std::string line;
+        auto info = reinterpret_cast<YueFormat*>(ud);
+        bool hasInBlockExp = false;
         if (defList) {
-                line += defList->to_string(ud);
+                for (auto def : defList->definitions.objects()) {
+                        auto argDef = static_cast<FnArgDef_t*>(def);
+                        if (argDef->defaultValue && isInBlockExp(argDef->defaultValue)) {
+                                hasInBlockExp = true;
+                                break;
+                        }
+                }
         }
-        if (shadowOption) {
-                line += (line.empty() ? ""s : " "s) + shadowOption->to_string(ud);
+        if (hasInBlockExp) {
+                str_list temp;
+                info->pushScope();
+                if (defList) {
+                        temp.push_back(defList->to_string(ud));
+                }
+                if (shadowOption) {
+                        temp.push_back(info->ind() + shadowOption->to_string(ud));
+                }
+                info->popScope();
+                return "(\n" + join(temp, "\n"sv) + '\n' + info->ind() + ')';
+        } else {
+                std::string line;
+                if (defList) {
+                        line += defList->to_string(ud);
+                }
+                if (shadowOption) {
+                        line += (line.empty() ? ""s : " "s) + shadowOption->to_string(ud);
+                }
+                return line.empty() ? (defList ? "()"s : ""s) : '(' + line + ')';
         }
-        return line.empty() ? ""s : '(' + line + ')';
 }
 std::string FunLit_t::to_string(void* ud) const {
         auto info = reinterpret_cast<YueFormat*>(ud);
@@ -1080,7 +1184,11 @@ std::string FunLit_t::to_string(void* ud) const {
                         line += ' ' + body->to_string(ud);
                 } else {
                         info->pushScope();
-                        line += '\n' + body->to_string(ud);
+                        auto bodyStr = body->to_string(ud);
+                        if (bodyStr.empty()) {
+                                bodyStr = info->ind() + "--"s;
+                        }
+                        line += '\n' + bodyStr;
                         info->popScope();
                 }
         }
@@ -1096,14 +1204,16 @@ std::string MacroLit_t::to_string(void* ud) const {
                 line = '(' + argsDef->to_string(ud) + ')';
         }
         line += "->"s;
-        if (body) {
-                if (body->content.is<Statement_t>()) {
-                        line += ' ' + body->to_string(ud);
-                } else {
-                        info->pushScope();
-                        line += '\n' + body->to_string(ud);
-                        info->popScope();
+        if (body->content.is<Statement_t>()) {
+                line += ' ' + body->to_string(ud);
+        } else {
+                info->pushScope();
+                auto bodyStr = body->to_string(ud);
+                if (bodyStr.empty()) {
+                        bodyStr = info->ind() + "--"s;
                 }
+                line += '\n' + bodyStr;
+                info->popScope();
         }
         return line;
 }
@@ -1113,14 +1223,16 @@ std::string Macro_t::to_string(void* ud) const {
 std::string MacroInPlace_t::to_string(void* ud) const {
         auto info = reinterpret_cast<YueFormat*>(ud);
         auto line = "$->"s;
-        if (body) {
-                if (body->content.is<Statement_t>()) {
-                        line += ' ' + body->to_string(ud);
-                } else {
-                        info->pushScope();
-                        line += '\n' + body->to_string(ud);
-                        info->popScope();
+        if (body->content.is<Statement_t>()) {
+                line += ' ' + body->to_string(ud);
+        } else {
+                info->pushScope();
+                auto bodyStr = body->to_string(ud);
+                if (bodyStr.empty()) {
+                        bodyStr = info->ind() + "--"s;
                 }
+                line += '\n' + bodyStr;
+                info->popScope();
         }
         return line;
 }
@@ -1135,15 +1247,32 @@ std::string AssignableNameList_t::to_string(void* ud) const {
         return join(temp, ", "sv);
 }
 std::string InvokeArgs_t::to_string(void* ud) const {
-        if (!args.empty() && ast_is<TableBlock_t>(args.back())) {
+        auto info = reinterpret_cast<YueFormat*>(ud);
+        bool hasInBlockExp = false;
+        for (auto arg : args.objects()) {
+                if (isInBlockExp(arg)) {
+                        hasInBlockExp = true;
+                        break;
+                }
+        }
+        if (hasInBlockExp) {
                 str_list temp;
+                bool newLine = false;
                 for (auto arg : args.objects()) {
-                        if (arg != args.back()) {
-                                temp.emplace_back(arg->to_string(ud));
+                        if (arg == args.front()) {
+                                if (ast_is<TableBlock_t>(arg)) {
+                                        newLine = true;
+                                }
+                                temp.push_back(arg->to_string(ud));
+                                info->pushScope();
+                        } else if (ast_is<TableBlock_t>(arg)) {
+                                temp.push_back(arg->to_string(ud));
+                        } else {
+                                temp.push_back(info->ind() + arg->to_string(ud));
                         }
                 }
-                auto list = join(temp, ", "sv);
-                return ' ' + list + (list.empty() ? ""s : ","s) + args.back()->to_string(ud);
+                info->popScope();
+                return (newLine ? '\n' : ' ') + join(temp, ",\n"sv);
         } else {
                 str_list temp;
                 for (auto arg : args.objects()) {
@@ -1203,10 +1332,29 @@ std::string StatementAppendix_t::to_string(void* ud) const {
 }
 std::string Statement_t::to_string(void* ud) const {
         std::string line;
-        if (appendix) {
-                return content->to_string(ud) + ' ' + appendix->to_string(ud);
+        if (!comments.empty()) {
+                auto info = reinterpret_cast<YueFormat*>(ud);
+                str_list temp;
+                for (ast_node* comment : comments.objects()) {
+                        if (comment == comments.front()) {
+                                temp.push_back(comment->to_string(ud));
+                        } else {
+                                temp.push_back(info->ind() + comment->to_string(ud));
+                        }
+                }
+                if (appendix) {
+                        temp.push_back(info->ind() + content->to_string(ud) + ' ' + appendix->to_string(ud));
+                        return join(temp, "\n"sv);
+                } else {
+                        temp.push_back(info->ind() + content->to_string(ud));
+                        return join(temp, "\n"sv);
+                }
         } else {
-                return content->to_string(ud);
+                if (appendix) {
+                        return content->to_string(ud) + ' ' + appendix->to_string(ud);
+                } else {
+                        return content->to_string(ud);
+                }
         }
 }
 std::string StatementSep_t::to_string(void*) const {
diff --git a/src/yuescript/yue_compiler.cpp b/src/yuescript/yue_compiler.cpp
index 3e60556..59f6d4b 100644
--- a/src/yuescript/yue_compiler.cpp
+++ b/src/yuescript/yue_compiler.cpp
@@ -75,7 +75,7 @@ static std::unordered_set<std::string> Metamethods = {
         "close"s // Lua 5.4
 };
 
-const std::string_view version = "0.21.1"sv;
+const std::string_view version = "0.21.2"sv;
 const std::string_view extension = "yue"sv;
 
 class CompileError : public std::logic_error {
diff --git a/src/yuescript/yue_parser.cpp b/src/yuescript/yue_parser.cpp
index 4b865f5..89791d6 100644
--- a/src/yuescript/yue_parser.cpp
+++ b/src/yuescript/yue_parser.cpp
@@ -477,7 +477,7 @@ YueParser::YueParser() {
                 space
         );
 
-        list_lit_lines = space_break >> list_lit_line >> *(-(space >> ',') >> space_break >> list_lit_line) >> -(space >> ',');
+        list_lit_lines = +space_break >> list_lit_line >> *(-(space >> ',') >> space_break >> list_lit_line) >> -(space >> ',');
 
         Comprehension = '[' >> not_('[') >>
                 Seperator >> space >> (
@@ -489,7 +489,6 @@ YueParser::YueParser() {
                         white >> ']' >> not_(space >> '=')
                 );
 
-        (space >> disable_for_rule(Exp) >> space >> CompInner >> space >> ']');
         CompValue = ',' >> space >> Exp;
         TblComprehension = and_('{') >> ('{' >> space >> disable_for_rule(Exp >> space >> -(CompValue >> space)) >> CompInner >> space >> '}' | braces_expression_error);
 
@@ -829,17 +828,26 @@ YueParser::YueParser() {
                 '*' >> space >> (SpreadExp | Exp | TableBlock)
         );
 
+        fn_arg_def_list = FnArgDef >> *(space >> ',' >> space >> FnArgDef);
+
+        fn_arg_def_lit_line = (
+                push_indent_match >> (space >> fn_arg_def_list >> pop_indent | pop_indent)
+        ) | (
+                space
+        );
+
+        fn_arg_def_lit_lines = fn_arg_def_lit_line >> *(-(space >> ',') >> space_break >> fn_arg_def_lit_line);
+
         FnArgDef = (Variable | SelfItem >> -ExistentialOp) >> -(space >> '=' >> space >> Exp);
 
-        FnArgDefList = Seperator >> ((
-                        FnArgDef >>
-                        *(space >> (',' | line_break) >> white >> FnArgDef) >>
-                        -(space >> (',' | line_break) >> white >> VarArg)
-                ) | VarArg);
+        FnArgDefList = Seperator >> (
+                fn_arg_def_lit_lines >> -(-(space >> ',') >> white >> VarArg) |
+                white >> VarArg
+        );
 
         OuterVarShadow = key("using") >> space >> (NameList | key("nil"));
 
-        FnArgsDef = '(' >> white >> -FnArgDefList >> -(space >> OuterVarShadow) >> white >> ')';
+        FnArgsDef = '(' >> *space_break >> -FnArgDefList >> -(white >> OuterVarShadow) >> white >> ')';
         FnArrow = expr("->") | "=>";
         FunLit = -FnArgsDef >> space >> FnArrow >> -(space >> Body);
 
@@ -873,8 +881,8 @@ YueParser::YueParser() {
 
         invoke_args_with_table =
                 ',' >> (
-                        TableBlock |
-                        space_break >> advance_match >> arg_block >> -arg_table_block
+                        arg_table_block |
+                        space_break >> advance_match >> arg_block >> -(-(space >> ',') >> arg_table_block)
                 ) | arg_table_block;
 
         leading_spaces_error = pl::user(+space_one >> '(' >> space >> Exp >> +(space >> ',' >> space >> Exp) >> space >> ')', [](const item_t& item) {
@@ -954,11 +962,10 @@ YueParser::YueParser() {
 
         Body = in_block | Statement;
 
-        empty_line_break = (
-                check_indent >> (multi_line_comment >> space | comment) |
-                advance >> ensure(multi_line_comment >> space | comment, pop_indent) |
-                plain_space
-        ) >> and_(stop);
+        empty_line_break =
+                check_indent >> (multi_line_comment >> space | comment) >> and_(stop) |
+                advance >> ensure(multi_line_comment >> space | comment, pop_indent) >> and_(stop) |
+                plain_space >> and_(line_break);
 
         indentation_error = pl::user(not_(pipe_operator | eof()), [](const item_t& item) {
                 throw ParserError("unexpected indent"sv, item.begin);
@@ -1084,6 +1091,11 @@ void trim(std::string& str) {
 } // namespace Utils
 
 std::string ParseInfo::errorMessage(std::string_view msg, int errLine, int errCol, int lineOffset) const {
+        if (!codes) {
+                std::ostringstream buf;
+                buf << errLine + lineOffset << ": "sv << msg;
+                return buf.str();
+        }
         const int ASCII = 255;
         int length = errLine;
         auto begin = codes->begin();
diff --git a/src/yuescript/yue_parser.h b/src/yuescript/yue_parser.h
index c3d5d7d..e183bf2 100644
--- a/src/yuescript/yue_parser.h
+++ b/src/yuescript/yue_parser.h
@@ -222,6 +222,9 @@ private:
         NONE_AST_RULE(fn_args_lit_line);
         NONE_AST_RULE(fn_args_lit_lines);
         NONE_AST_RULE(fn_args);
+        NONE_AST_RULE(fn_arg_def_list);
+        NONE_AST_RULE(fn_arg_def_lit_line);
+        NONE_AST_RULE(fn_arg_def_lit_lines);
         NONE_AST_RULE(destruct_def);
         NONE_AST_RULE(macro_args_def);
         NONE_AST_RULE(chain_call);
diff --git a/src/yuescript/yuescript.cpp b/src/yuescript/yuescript.cpp
index 856d8f3..dbaa287 100644
--- a/src/yuescript/yuescript.cpp
+++ b/src/yuescript/yuescript.cpp
@@ -172,6 +172,39 @@ static int yuetolua(lua_State* L) {
         return 3;
 }
 
+static int yueformat(lua_State* L) {
+        size_t len = 0;
+        auto input = luaL_checklstring(L, 1, &len);
+        int tabSize = 0;
+        if (!lua_isnoneornil(L, 2)) {
+                tabSize = static_cast<int>(luaL_checkinteger(L, 2));
+        }
+        std::string_view codes(input, len);
+        auto info = yue::YueParser{}.parse<yue::File_t>(codes);
+        if (info.error) {
+                const auto& error = info.error.value();
+                if (!info.codes) {
+                        lua_pushnil(L);
+                        lua_pushlstring(L, error.msg.c_str(), error.msg.size());
+                        return 2;
+                }
+                auto displayMessage = info.errorMessage(error.msg, error.line, error.col, 0);
+                lua_pushnil(L);
+                lua_pushlstring(L, displayMessage.c_str(), displayMessage.size());
+                return 2;
+        }
+        yue::YueFormat formatter{};
+        if (tabSize > 0) {
+                formatter.spaceOverTab = true;
+                formatter.tabSpaces = tabSize;
+        } else {
+                formatter.spaceOverTab = false;
+        }
+        auto result = formatter.toString(info.node.get());
+        lua_pushlstring(L, result.c_str(), result.size());
+        return 1;
+}
+
 static int yuecheck(lua_State* L) {
         size_t len = 0;
         auto input = luaL_checklstring(L, 1, &len);
@@ -268,6 +301,7 @@ static int yuetoast(lua_State* L) {
                         stack.pop();
                 };
                 do_call(info.node);
+                yue::YueFormat formatter{};
                 while (!stack.empty()) {
                         auto& current = stack.top();
                         int continuation = current.continuation;
@@ -319,7 +353,8 @@ static int yuetoast(lua_State* L) {
                                                         lua_rawseti(L, -2, 2);
                                                         lua_pushinteger(L, node->m_begin.m_col);
                                                         lua_rawseti(L, -2, 3);
-                                                        auto str = parser.toString(node);
+                                                        formatter.indent = 0;
+                                                        auto str = node->to_string(&formatter);
                                                         yue::Utils::trim(str);
                                                         lua_pushlstring(L, str.c_str(), str.length());
                                                         lua_rawseti(L, -2, 4);
@@ -371,8 +406,9 @@ static int yuetoast(lua_State* L) {
                 return 1;
         } else {
                 lua_pushnil(L);
-                const auto& msg = info.error.value().msg;
-                lua_pushlstring(L, msg.c_str(), msg.length());
+                const auto& err = info.error.value();
+                auto displayMessage = info.errorMessage(err.msg, err.line, err.col);
+                lua_pushlstring(L, displayMessage.c_str(), displayMessage.length());
                 return 2;
         }
 }
@@ -381,6 +417,7 @@ static const luaL_Reg yuelib[] = {
         {"to_lua", yuetolua},
         {"to_ast", yuetoast},
         {"check", yuecheck},
+        {"format", yueformat},
         {"version", nullptr},
         {"options", nullptr},
         {"load_stacktraceplus", nullptr},