diff --git a/makefile b/makefile
index cc9ecfc..7db2e34 100644
--- a/makefile
+++ b/makefile
@@ -84,7 +84,6 @@ build/nasal_ast.o: \
 build/nasal_builtin.o: \
 	src/nasal.h\
 	src/nasal_gc.h\
-	src/fg_props.h\
 	src/nasal_builtin.h src/nasal_builtin.cpp | build
 	$(CXX) -std=$(STD) -c -O3 src/nasal_builtin.cpp -fno-exceptions -fPIC -o build/nasal_builtin.o -I .
 
diff --git a/src/fg_props.cpp b/src/fg_props.cpp
index 32f470b..206f267 100644
--- a/src/fg_props.cpp
+++ b/src/fg_props.cpp
@@ -28,4 +28,9 @@ var builtin_logprint(var* local, gc& ngc) {
     }
     out << "\n";
     return nil;
-}
\ No newline at end of file
+}
+
+nasal_builtin_table flight_gear_native[] = {
+    {"_logprint", builtin_logprint},
+    {nullptr, nullptr}
+};
\ No newline at end of file
diff --git a/src/fg_props.h b/src/fg_props.h
index 852f3a6..59d136c 100644
--- a/src/fg_props.h
+++ b/src/fg_props.h
@@ -2,6 +2,7 @@
 
 #include "nasal.h"
 #include "nasal_gc.h"
+#include "nasal_builtin.h"
 
 #define SG_LOG_BULK 1
 #define SG_LOG_DEBUG 2
@@ -12,4 +13,6 @@
 #define SG_DEV_ALERT 8
 #define SG_MANDATORY_INFO 9
 
-var builtin_logprint(var*, gc&);
\ No newline at end of file
+var builtin_logprint(var*, gc&);
+
+extern nasal_builtin_table flight_gear_native[];
diff --git a/src/nasal_builtin.cpp b/src/nasal_builtin.cpp
index eef53ff..4ceed8e 100644
--- a/src/nasal_builtin.cpp
+++ b/src/nasal_builtin.cpp
@@ -1,5 +1,4 @@
 #include "nasal_builtin.h"
-#include "fg_props.h"
 #include <chrono>
 
 var builtin_print(var* local, gc& ngc) {
@@ -1374,6 +1373,5 @@ nasal_builtin_table builtin[] = {
     {"__gcinfo", builtin_gcinfo},
     {"__logtime", builtin_logtime},
     {"__ghosttype", builtin_ghosttype},
-    {"_logprint", builtin_logprint},
     {nullptr, nullptr}
 };
\ No newline at end of file
diff --git a/src/nasal_builtin.h b/src/nasal_builtin.h
index 3cd7974..d14d62d 100644
--- a/src/nasal_builtin.h
+++ b/src/nasal_builtin.h
@@ -134,7 +134,7 @@ var builtin_ghosttype(var*, gc&);
 // this table must end with {nullptr,nullptr}
 struct nasal_builtin_table {
     const char* name;
-    var (*func)(var*,gc&);
+    var (*func)(var*, gc&);
 };
 
 extern nasal_builtin_table builtin[];
diff --git a/src/nasal_codegen.cpp b/src/nasal_codegen.cpp
index b1adddb..b3b7753 100644
--- a/src/nasal_codegen.cpp
+++ b/src/nasal_codegen.cpp
@@ -1,15 +1,30 @@
 #include "nasal_codegen.h"
 
+void codegen::load_native_function_table(nasal_builtin_table* table) {
+    for(usize i = 0; table[i].func; ++i) {
+        if (native_function_mapper.count(table[i].name)) {
+            err.err("code", "\"" + std::string(table[i].name) + "\" conflicts.");
+            continue;
+        }
+        native_function.push_back(table[i]);
+        auto index = native_function_mapper.size();
+        native_function_mapper[table[i].name] = index;
+    }
+}
+
+void codegen::init_native_function() {
+    load_native_function_table(builtin);
+    load_native_function_table(flight_gear_native);
+}
+
 void codegen::check_id_exist(identifier* node) {
     const auto& name = node->get_name();
-    for(u32 i = 0; builtin[i].name; ++i) {
-        if (builtin[i].name==name) {
-            if (local.empty()) {
-                die("native function used in global scope",
-                    node->get_location());
-            }
-            return;
+    if (native_function_mapper.count(name)) {
+        if (local.empty()) {
+            die("native function should not be used in global scope",
+                node->get_location());
         }
+        return;
     }
 
     if (local_find(name)>=0) {
@@ -269,16 +284,17 @@ void codegen::call_gen(call_expr* node) {
 
 void codegen::call_id(identifier* node) {
     const auto& name = node->get_name();
-    for(u32 i = 0; builtin[i].name; ++i) {
-        if (builtin[i].name==name) {
-            gen(op_callb, i, node->get_location());
-            if (local.empty()) {
-                die("should warp native function in local scope",
-                    node->get_location());
-            }
-            return;
+    if (native_function_mapper.count(name)) {
+        gen(op_callb,
+            static_cast<u32>(native_function_mapper.at(name)),
+            node->get_location());
+        if (local.empty()) {
+            die("should warp native function in local scope",
+                node->get_location());
         }
+        return;
     }
+
     i32 index;
     if ((index=local_find(name))>=0) {
         gen(op_calll, index, node->get_location());
@@ -384,12 +400,11 @@ void codegen::mcall(expr* node) {
 
 void codegen::mcall_id(identifier* node) {
     const auto& name = node->get_name();
-    for(u32 i = 0; builtin[i].name; ++i) {
-        if (builtin[i].name==name) {
-            die("cannot modify native function", node->get_location());
-            return;
-        }
+    if (native_function_mapper.count(name)) {
+        die("cannot modify native function", node->get_location());
+        return;
     }
+
     i32 index;
     if ((index=local_find(name))>=0) {
         gen(op_mcalll, index, node->get_location());
@@ -1114,6 +1129,7 @@ void codegen::ret_gen(return_expr* node) {
 }
 
 const error& codegen::compile(parse& parse, linker& import) {
+    init_native_function();
     const auto& file = import.filelist();
     file_map = {};
     for(usize i = 0; i<file.size(); ++i) {
@@ -1175,7 +1191,10 @@ void codegen::print(std::ostream& out) {
     }
 
     // print code
-    codestream::set(const_number_table.data(), const_string_table.data());
+    codestream::set(
+        const_number_table.data(),
+        const_string_table.data(),
+        native_function.data());
     for(u32 i = 0; i<code.size(); ++i) {
         // print opcode index, opcode name, opcode immediate number
         const auto& c = code[i];
diff --git a/src/nasal_codegen.h b/src/nasal_codegen.h
index dc8a683..2e8ca94 100644
--- a/src/nasal_codegen.h
+++ b/src/nasal_codegen.h
@@ -1,7 +1,6 @@
 #pragma once
 
 #include "nasal_err.h"
-#include "nasal_builtin.h"
 #include "nasal_opcode.h"
 #include "nasal_ast.h"
 #include "ast_visitor.h"
@@ -9,6 +8,9 @@
 #include "nasal_parse.h"
 #include "nasal_import.h"
 
+#include "nasal_builtin.h"
+#include "fg_props.h"
+
 #include <iomanip>
 #include <list>
 #include <stack>
@@ -36,6 +38,12 @@ private:
     std::vector<f64> const_number_table;
     std::vector<std::string> const_string_table;
 
+    // native functions
+    std::vector<nasal_builtin_table> native_function;
+    std::unordered_map<std::string, usize> native_function_mapper;
+    void load_native_function_table(nasal_builtin_table*);
+    void init_native_function();
+
     // generated opcodes
     std::vector<opcode> code;
 
@@ -108,6 +116,7 @@ private:
 public:
     const auto& strs() const {return const_string_table;}
     const auto& nums() const {return const_number_table;}
+    const auto& natives() const {return native_function;}
     const auto& codes() const {return code;}
     const auto& globals() const {return global;}
     const auto& get_experimental_namespace() const {
diff --git a/src/nasal_dbg.cpp b/src/nasal_dbg.cpp
index 66b73f6..cd50eff 100644
--- a/src/nasal_dbg.cpp
+++ b/src/nasal_dbg.cpp
@@ -91,7 +91,7 @@ void dbg::step_info() {
 
     begin = (ctx.pc>>3)==0? 0:((ctx.pc>>3)<<3);
     end = (1+(ctx.pc>>3))<<3;
-    codestream::set(cnum, cstr, files);
+    codestream::set(cnum, cstr, native.data(), files);
     std::clog << "next bytecode:\n";
     for(u32 i = begin; i<end && bytecode[i].op!=op_exit; ++i) {
         std::clog
@@ -164,12 +164,8 @@ void dbg::run(
     const std::vector<std::string>& argv) {
     verbose = true;
     fsize = linker.filelist().size();
-    init(gen.strs(),
-         gen.nums(),
-         gen.codes(),
-         gen.globals(),
-         linker.filelist(),
-         argv);
+    init(gen.strs(), gen.nums(), gen.natives(),
+         gen.codes(), gen.globals(), linker.filelist(), argv);
     u64 count[op_ret+1] = {0};
     typedef void (dbg::*nafunc)();
     const nafunc oprs[] = {
diff --git a/src/nasal_gc.h b/src/nasal_gc.h
index a5c0f7d..539104c 100644
--- a/src/nasal_gc.h
+++ b/src/nasal_gc.h
@@ -344,7 +344,7 @@ struct gc {
     context* rctx = nullptr;
     nas_co* cort = nullptr; // running coroutine
 
-    /*  temporary space used in builtin/module functions */
+    /*  temporary space used in native/module functions */
     var temp = nil;
 
     /* constants and memory pool */
diff --git a/src/nasal_opcode.cpp b/src/nasal_opcode.cpp
index f02dee8..00d0e26 100644
--- a/src/nasal_opcode.cpp
+++ b/src/nasal_opcode.cpp
@@ -26,12 +26,14 @@ const char* opname[] = {
 };
 
 void codestream::set(
-    const f64* numbuff,
-    const std::string* strbuff,
-    const std::string* filelist) {
-    nums = numbuff;
-    strs = strbuff;
-    files = filelist;
+    const f64* num_buff,
+    const std::string* str_buff,
+    const nasal_builtin_table* native_table_ptr,
+    const std::string* file_list) {
+    nums = num_buff;
+    strs = str_buff;
+    natives = native_table_ptr;
+    files = file_list;
 }
 
 void codestream::dump(std::ostream& out) const {
@@ -87,8 +89,8 @@ void codestream::dump(std::ostream& out) const {
         case op_loadl:
             out << hex << "0x" << num << dec; break;
         case op_callb:
-            out << hex << "0x" << num << " <" << builtin[num].name
-                << "@0x" << (u64)builtin[num].func << dec << ">"; break;
+            out << hex << "0x" << num << " <" << natives[num].name
+                << "@0x" << (u64)natives[num].func << dec << ">"; break;
         case op_upval: case op_mupval:
         case op_loadu:
             out << hex << "0x" << ((num>>16)&0xffff)
diff --git a/src/nasal_opcode.h b/src/nasal_opcode.h
index 0496e6b..d7f93fc 100644
--- a/src/nasal_opcode.h
+++ b/src/nasal_opcode.h
@@ -57,16 +57,16 @@ enum op_code_type:u8 {
     op_divecp, // /= const and pop stack top
     op_lnkecp, // ~= concat const std::string and pop stack top
     op_meq,    // = maybe pop stack top
-    op_eq,     // ==
-    op_neq,    // !=
-    op_less,   // <
-    op_leq,    // <=
-    op_grt,    // >
-    op_geq,    // >=
-    op_lessc,  // < const
-    op_leqc,   // <= const
-    op_grtc,   // > const
-    op_geqc,   // >= const
+    op_eq,     // == compare operator
+    op_neq,    // != compare operator
+    op_less,   // < compare operator
+    op_leq,    // <= compare operator
+    op_grt,    // > compare operator
+    op_geq,    // >= compare operator
+    op_lessc,  // < const compare operator
+    op_leqc,   // <= const compare operator
+    op_grtc,   // > const compare operator
+    op_geqc,   // >= const compare operator
     op_pop,    // pop a value out of stack top
     op_jmp,    // jump absolute address with no condition
     op_jt,     // used in operator and/or,jmp when condition is true and DO NOT POP
@@ -82,8 +82,8 @@ enum op_code_type:u8 {
     op_callh,  // call hash.label
     op_callfv, // call function(vector as parameters)
     op_callfh, // call function(hash as parameters)
-    op_callb,  // call builtin-function
-    op_slcbeg, // begin of slice like: vec[1,2,3:6,0,-1]
+    op_callb,  // call native functions
+    op_slcbeg, // begin of slice like: vec[1, 2, 3:6, 0, -1]
     op_slcend, // end of slice
     op_slc,    // slice like vec[1]
     op_slc2,   // slice like vec[nil:10]
@@ -111,10 +111,16 @@ private:
     const u32 index;
     inline static const f64* nums = nullptr;
     inline static const std::string* strs = nullptr;
+    inline static const nasal_builtin_table* natives = nullptr;
     inline static const std::string* files = nullptr;
+    
 public:
     codestream(const opcode& c, const u32 i): code(c), index(i) {}
-    static void set(const f64*, const std::string*, const std::string* filelist = nullptr);
+    static void set(
+        const f64*, const std::string*,
+        const nasal_builtin_table*,
+        const std::string* file_list = nullptr
+    );
     void dump(std::ostream&) const;
 };
 
diff --git a/src/nasal_vm.cpp b/src/nasal_vm.cpp
index dcf00ee..7ac75e4 100644
--- a/src/nasal_vm.cpp
+++ b/src/nasal_vm.cpp
@@ -3,6 +3,7 @@
 void vm::init(
     const std::vector<std::string>& strs,
     const std::vector<f64>& nums,
+    const std::vector<nasal_builtin_table>& natives,
     const std::vector<opcode>& code,
     const std::unordered_map<std::string, i32>& global,
     const std::vector<std::string>& filenames,
@@ -13,6 +14,9 @@ void vm::init(
     bytecode = code.data();
     files = filenames.data();
 
+    /* set native functions */
+    native = natives;
+
     /* set canary and program counter */
     ctx.pc = 0;
     ctx.localr = nullptr;
@@ -98,7 +102,7 @@ void vm::traceback() {
     std::clog << "trace back ("
               << (ngc.rctx->stack==stack? "main":"coroutine")
               << ")\n";
-    codestream::set(cnum, cstr, files);
+    codestream::set(cnum, cstr, native.data(), files);
     for(u32 p = 0, same = 0, prev = 0xffffffff; !ret.empty(); prev = p, ret.pop()) {
         if ((p = ret.top())==prev) {
             ++same;
@@ -230,12 +234,8 @@ void vm::run(
     const std::vector<std::string>& argv,
     const bool detail) {
     verbose = detail;
-    init(gen.strs(),
-         gen.nums(),
-         gen.codes(),
-         gen.globals(),
-         linker.filelist(),
-         argv);
+    init(gen.strs(), gen.nums(), gen.natives(),
+         gen.codes(), gen.globals(), linker.filelist(), argv);
 #ifndef _MSC_VER
     // using labels as values/computed goto
     const void* oprs[] = {
diff --git a/src/nasal_vm.h b/src/nasal_vm.h
index c9ab6d5..92a7a64 100644
--- a/src/nasal_vm.h
+++ b/src/nasal_vm.h
@@ -33,11 +33,13 @@ protected:
     /* values used for debugger */
     const std::string* files = nullptr; // file name list
     const opcode* bytecode = nullptr; // bytecode buffer address
+    std::vector<nasal_builtin_table> native;
 
     /* vm initializing function */
     void init(
         const std::vector<std::string>&,
         const std::vector<f64>&,
+        const std::vector<nasal_builtin_table>&,
         const std::vector<opcode>&,
         const std::unordered_map<std::string, i32>&,
         const std::vector<std::string>&,
@@ -739,13 +741,13 @@ inline void vm::o_callfh() {
 }
 
 inline void vm::o_callb() {
-    // reserve place for builtin function return,
+    // reserve place for native function return,
     // this code is written for coroutine
     (++ctx.top)[0] = nil;
 
-    // if running a builtin function about coroutine
+    // if running a native function about coroutine
     // (top) will be set to another context.top, instead of main_context.top
-    var tmp = (*builtin[imm[ctx.pc]].func)(ctx.localr, ngc);
+    var tmp = (*native[imm[ctx.pc]].func)(ctx.localr, ngc);
 
     // so we use tmp variable to store this return value
     // and set it to top[0] later
@@ -753,7 +755,7 @@ inline void vm::o_callb() {
 
     // if get none, this means errors occurred when calling this native function
     if (ctx.top[0].type==vm_none) {
-        die("native function error");
+        die("error occurred in native function");
         return;
     }
 }
@@ -780,7 +782,7 @@ inline void vm::o_slc() {
     var val = (ctx.top--)[0];
     var res = ctx.top[-1].vec().get_val(val.tonum());
     if (res.type==vm_none) {
-        die("index "+std::to_string(val.tonum())+" out of range");
+        die("index " + std::to_string(val.tonum()) + " out of range");
         return;
     }
     ctx.top[0].vec().elems.push_back(res);
@@ -806,7 +808,8 @@ inline void vm::o_slc2() {
     }
 
     if (num1<-size || num1>=size || num2<-size || num2>=size) {
-        die("index "+std::to_string(num1)+":"+std::to_string(num2)+" out of range");
+        die("index " + std::to_string(num1) + ":" +
+            std::to_string(num2) + " out of range");
         return;
     } else if (num1<=num2) {
         for(i32 i = num1; i<=num2; ++i) {