diff --git a/CMakeLists.txt b/CMakeLists.txt
index a2a6f13..ef2d704 100644
--- a/CMakeLists.txt
+++ b/CMakeLists.txt
@@ -38,7 +38,8 @@ set(NASAL_OBJECT_SOURCE_FILE
     ${CMAKE_SOURCE_DIR}/src/nasal_parse.cpp
     ${CMAKE_SOURCE_DIR}/src/nasal_vm.cpp
     ${CMAKE_SOURCE_DIR}/src/optimizer.cpp
-    ${CMAKE_SOURCE_DIR}/src/symbol_finder.cpp)
+    ${CMAKE_SOURCE_DIR}/src/symbol_finder.cpp
+    ${CMAKE_SOURCE_DIR}/src/repl.cpp)
 add_library(nasal-object STATIC ${NASAL_OBJECT_SOURCE_FILE})
 target_include_directories(nasal-object PRIVATE ${CMAKE_SOURCE_DIR}/src)
 
diff --git a/makefile b/makefile
index 456f98d..1f94936 100644
--- a/makefile
+++ b/makefile
@@ -23,7 +23,8 @@ NASAL_HEADER=\
 	src/math_lib.h\
 	src/dylib_lib.h\
 	src/unix_lib.h\
-	src/coroutine.h
+	src/coroutine.h\
+	src/repl.h
 
 NASAL_OBJECT=\
 	build/nasal_err.o\
@@ -49,6 +50,7 @@ NASAL_OBJECT=\
 	build/coroutine.o\
 	build/nasal_vm.o\
 	build/nasal_dbg.o\
+	build/repl.o\
 	build/main.o
 
 # for test
@@ -67,6 +69,9 @@ build/main.o: $(NASAL_HEADER) src/main.cpp | build
 build/nasal_misc.o: src/nasal.h src/nasal_misc.cpp | build
 	$(CXX) -std=$(STD) -c -O3 src/nasal_misc.cpp -fno-exceptions -fPIC -o build/nasal_misc.o -I .
 
+build/repl.o: src/nasal.h src/repl.h src/repl.cpp | build
+	$(CXX) -std=$(STD) -c -O3 src/repl.cpp -fno-exceptions -fPIC -o build/repl.o -I .
+
 build/nasal_err.o: src/nasal.h src/nasal_err.h src/nasal_err.cpp | build
 	$(CXX) -std=$(STD) -c -O3 src/nasal_err.cpp -fno-exceptions -fPIC -o build/nasal_err.o -I .
 
diff --git a/src/main.cpp b/src/main.cpp
index 6867690..c1fb578 100644
--- a/src/main.cpp
+++ b/src/main.cpp
@@ -11,21 +11,22 @@
 #include "nasal_codegen.h"
 #include "nasal_vm.h"
 #include "nasal_dbg.h"
+#include "repl.h"
 
 #include <unordered_map>
 #include <thread>
 #include <cstdlib>
 
-const u32 VM_RAW_AST  = 1;
-const u32 VM_AST      = 1<<1;
-const u32 VM_CODE     = 1<<2;
-const u32 VM_TIME     = 1<<3;
-const u32 VM_EXEC     = 1<<4;
-const u32 VM_DETAIL   = 1<<5;
-const u32 VM_DEBUG    = 1<<6;
-const u32 VM_SYMINFO  = 1<<7;
-const u32 VM_PROFILE  = 1<<8;
-const u32 VM_PROF_ALL = 1<<9;
+const u32 VM_RAW_AST   = 1;
+const u32 VM_AST       = 1<<1;
+const u32 VM_CODE      = 1<<2;
+const u32 VM_TIME      = 1<<3;
+const u32 VM_EXEC      = 1<<4;
+const u32 VM_DETAIL    = 1<<5;
+const u32 VM_DEBUG     = 1<<6;
+const u32 VM_SYMINFO   = 1<<7;
+const u32 VM_PROFILE   = 1<<8;
+const u32 VM_PROF_ALL  = 1<<9;
 
 std::ostream& help(std::ostream& out) {
     out
@@ -53,6 +54,7 @@ std::ostream& help(std::ostream& out) {
     << "         --prof     | show profiling result, available under debug mode.\n"
     << "         --prof-all | show profiling result of all files,"
     << "available under debug mode.\n"
+    << "   -r,   --repl     | use repl interpreter(experimental).\n"
     << "file:\n"
     << "   <filename>       | execute file.\n"
     << "argv:\n"
@@ -129,9 +131,8 @@ void execute(
     ld.link(parse, file, cmd&VM_DETAIL).chkerr();
     
     // optimizer does simple optimization on ast
-    auto opt = new optimizer;
+    auto opt = std::unique_ptr<optimizer>(new optimizer);
     opt->do_optimization(parse.tree());
-    delete opt;
     if (cmd&VM_AST) {
         auto dumper = std::unique_ptr<ast_dumper>(new ast_dumper);
         dumper->dump(parse.tree());
@@ -178,6 +179,9 @@ i32 main(i32 argc, const char* argv[]) {
             std::clog << help;
         } else if (s=="-v" || s=="--version") {
             std::clog << version;
+        } else if (s=="-r" || s=="--repl") {
+            auto repl_module = std::unique_ptr<repl::repl>(new repl::repl);
+            repl_module->execute();
         } else if (s[0]!='-') {
             execute(s, {}, VM_EXEC);
         } else {
diff --git a/src/nasal_codegen.cpp b/src/nasal_codegen.cpp
index 28477c8..9a9fc1a 100644
--- a/src/nasal_codegen.cpp
+++ b/src/nasal_codegen.cpp
@@ -1144,7 +1144,7 @@ void codegen::ret_gen(return_expr* node) {
     gen(op_ret, 0, node->get_location());
 }
 
-const error& codegen::compile(parse& parse, linker& import, bool repl) {
+const error& codegen::compile(parse& parse, linker& import) {
     init_native_function();
     init_file_map(import.get_file_list());
 
@@ -1157,7 +1157,7 @@ const error& codegen::compile(parse& parse, linker& import, bool repl) {
 
     // search global symbols first
     find_symbol(parse.tree());
-    gen(op_intg, repl? STACK_DEPTH/2:global.size(), parse.tree()->get_location());
+    gen(op_intg, global.size(), parse.tree()->get_location());
 
     // generate main block
     block_gen(parse.tree());
diff --git a/src/nasal_codegen.h b/src/nasal_codegen.h
index 141f75b..121befc 100644
--- a/src/nasal_codegen.h
+++ b/src/nasal_codegen.h
@@ -132,7 +132,7 @@ public:
 
 public:
     codegen() = default;
-    const error& compile(parse&, linker&, bool repl = false);
+    const error& compile(parse&, linker&);
     void print(std::ostream&);
     void symbol_dump(std::ostream&) const;
 };
diff --git a/src/repl.cpp b/src/repl.cpp
new file mode 100644
index 0000000..3be8f19
--- /dev/null
+++ b/src/repl.cpp
@@ -0,0 +1,137 @@
+#include "repl.h"
+#include "nasal_lexer.h"
+#include "nasal_parse.h"
+#include "nasal_import.h"
+#include "optimizer.h"
+#include "nasal_codegen.h"
+#include "nasal_vm.h"
+
+namespace repl {
+
+std::string repl::readline(std::string prompt = ">>> ") {
+    auto line = std::string("");
+    std::cout << prompt;
+    std::getline(std::cin, line,'\n');
+    return line;
+}
+
+void repl::update_temp_file() {
+    auto content = std::string("");
+    for(const auto& i : source) {
+        content += i + "\n";
+    }
+
+    std::ofstream out(".temp.nas", std::ios::binary);
+    out << content;
+}
+
+bool repl::check_need_more_input() {
+    while(true) {
+        update_temp_file();
+        auto nasal_lexer = std::unique_ptr<lexer>(new lexer);
+        if (nasal_lexer->scan(".temp.nas").geterr()) {
+            return false;
+        }
+
+        i64 in_curve = 0;
+        i64 in_bracket = 0;
+        i64 in_brace = 0;
+        for(const auto& t : nasal_lexer->result()) {
+            switch(t.type) {
+                case tok::lcurve: ++in_curve; break;
+                case tok::rcurve: --in_curve; break;
+                case tok::lbracket: ++in_bracket; break;
+                case tok::rbracket: --in_bracket; break;
+                case tok::lbrace: ++in_brace; break;
+                case tok::rbrace: --in_brace; break;
+                default: break;
+            }
+        }
+        if (!in_curve && !in_bracket && !in_brace) {
+            break;
+        }
+        auto line = readline("... ");
+        source.back() += "\n" + line;
+    }
+    return true;
+}
+
+void repl::help() {
+    std::cout << ".h, .help  | show help\n";
+    std::cout << ".e, .exit  | quit the REPL\n";
+    std::cout << ".q, .quit  | quit the REPL\n";
+    std::cout << ".c, .clear | clear the screen\n";
+    std::cout << "\n";
+}
+
+bool repl::run() {
+    update_temp_file();
+
+    auto nasal_lexer = std::unique_ptr<lexer>(new lexer);
+    auto nasal_parser = std::unique_ptr<parse>(new parse);
+    auto nasal_linker = std::unique_ptr<linker>(new linker);
+    auto nasal_opt = std::unique_ptr<optimizer>(new optimizer);
+    auto nasal_codegen = std::unique_ptr<codegen>(new codegen);
+    auto nasal_runtime = std::unique_ptr<vm>(new vm);
+
+    if (nasal_lexer->scan(".temp.nas").geterr()) {
+        return false;
+    }
+
+    if (nasal_parser->compile(*nasal_lexer).geterr()) {
+        return false;
+    }
+
+    if (nasal_linker->link(*nasal_parser, ".temp.nas", true).geterr()) {
+        return false;
+    }
+
+    nasal_opt->do_optimization(nasal_parser->tree());
+    if (nasal_codegen->compile(*nasal_parser, *nasal_linker).geterr()) {
+        return false;
+    }
+
+    nasal_runtime->run(*nasal_codegen, *nasal_linker, {}, false);
+
+    return true;
+}
+
+void repl::execute() {
+    source = {};
+    std::cout << "Nasal REPL interpreter(experimental).\n";
+    help();
+
+    while(true) {
+        auto line = readline();
+        if (!line.length()) {
+            continue;
+        }
+
+        if (line == ".e" || line == ".exit" || line == ".q" || line == ".quit") {
+            break;
+        } else if (line == ".h" || line == ".help") {
+            help();
+            continue;
+        } else if (line == ".c" || line == ".clear") {
+            std::cout << "\033c";
+            continue;
+        } else if (line[0] == "."[0]) {
+            std::cout << "no such command \"" << line;
+            std::cout << "\", input \".help\" for help\n";
+            continue;
+        }
+
+        source.push_back(line);
+        if (!check_need_more_input()) {
+            source.pop_back();
+            continue;
+        }
+
+        if (!run()) {
+            source.pop_back();
+        }
+        std::cout << "\n";
+    }
+}
+
+}
\ No newline at end of file
diff --git a/src/repl.h b/src/repl.h
new file mode 100644
index 0000000..3a2ef8a
--- /dev/null
+++ b/src/repl.h
@@ -0,0 +1,28 @@
+#pragma once
+
+#include "nasal.h"
+
+#include <iostream>
+#include <fstream>
+#include <vector>
+#include <cstring>
+#include <sstream>
+
+namespace repl {
+
+class repl {
+private:
+    std::vector<std::string> source;
+
+private:
+    std::string readline(std::string);
+    bool check_need_more_input();
+    void update_temp_file();
+    void help();
+    bool run();
+
+public:
+    void execute();
+};
+
+}
\ No newline at end of file
diff --git a/tools/repl.nas b/tools/repl.nas
index 12d388e..74a3cc2 100644
--- a/tools/repl.nas
+++ b/tools/repl.nas
@@ -31,6 +31,9 @@ var count_bracket = func(line) {
 
 while(1) {
     var line = readline(">>> ");
+    if (!size(line)) {
+        continue;
+    }
     if (line == ".exit" or line == ".quit") {
         break;
     } elsif (line == ".help") {