diff --git a/makefile b/makefile
index 031925d..8e0c434 100644
--- a/makefile
+++ b/makefile
@@ -1,11 +1,13 @@
 STD = c++17
-OS = $(shell uname)
+
+ifndef OS
+	OS = $(shell uname)
+endif
 ifeq ($(OS), Darwin)
 	CXXFLAGS = -std=$(STD) -c -O3 -fno-exceptions -fPIC -mmacosx-version-min=10.15
 else
 	CXXFLAGS = -std=$(STD) -c -O3 -fno-exceptions -fPIC
 endif
-CPPFLAGS = -I .
 
 NASAL_HEADER=\
 	src/ast_dumper.h\
diff --git a/module/fib.cpp b/module/fib.cpp
index 1e81a99..9d570ef 100644
--- a/module/fib.cpp
+++ b/module/fib.cpp
@@ -62,7 +62,7 @@ var set_new_ghost(var* args, usize size, gc* ngc) {
         return nil;
     }
     f64 num = args[1].num();
-    *((u32*)res.obj().ptr) = static_cast<u32>(num);
+    *((u32*)res.obj().pointer) = static_cast<u32>(num);
     std::cout << "set_new_ghost: successfully set ghost = " << num << "\n";
     return nil;
 }
@@ -74,7 +74,7 @@ var print_new_ghost(var* args, usize size, gc* ngc) {
         return nil;
     }
     std::cout << "print_new_ghost: " << res.obj() << " result = "
-        << *((u32*)res.obj().ptr) << "\n";
+        << *((u32*)res.obj().pointer) << "\n";
     return nil;
 }
 
diff --git a/module/makefile b/module/makefile
index be81a35..5c9ab1c 100644
--- a/module/makefile
+++ b/module/makefile
@@ -7,7 +7,10 @@ used_header = ../src/nasal.h ../src/nasal_gc.h
 used_object = ../build/nasal_misc.o ../build/nasal_gc.o
 
 STD = c++17
-OS = $(shell uname)
+
+ifndef OS
+	OS = $(shell uname)
+endif
 ifeq ($(OS), Darwin)
 	CXXFLAGS = -std=$(STD) -c -O3 -fPIC -mmacosx-version-min=10.15
 else
diff --git a/src/coroutine.cpp b/src/coroutine.cpp
index 5df1397..319698e 100644
--- a/src/coroutine.cpp
+++ b/src/coroutine.cpp
@@ -17,10 +17,16 @@ var builtin_cocreate(var* local, gc& ngc) {
     // +-------------+
     var func = local[1];
     if (func.type!=vm_func) {
-        return nas_err("coroutine::create", "must use a function to create coroutine");
+        return nas_err(
+            "coroutine::create",
+            "must use a function to create coroutine"
+        );
     }
     if (ngc.cort) {
-        return nas_err("coroutine::create", "cannot create another coroutine in a coroutine");
+        return nas_err(
+            "coroutine::create",
+            "cannot create another coroutine in a coroutine"
+        );
     }
     var co = ngc.alloc(vm_co);
     nas_co& cort = co.co();
@@ -30,13 +36,18 @@ var builtin_cocreate(var* local, gc& ngc) {
     cort.ctx.localr = cort.ctx.top+1;
     cort.ctx.top = cort.ctx.localr+func.func().local_size;
     cort.ctx.localr[0] = func.func().local[0];
-    cort.ctx.top[0] = nil; // old upvalr
+    // store old upvalr on stack
+    cort.ctx.top[0] = nil;
     cort.ctx.top++;
-    cort.ctx.top[0] = var::addr((var*)nullptr); // old localr
+    // store old localr on stack
+    cort.ctx.top[0] = var::addr((var*)nullptr);
     cort.ctx.top++;
-    cort.ctx.top[0] = var::ret(0); // old pc, set to zero to make op_ret recognizing this as coroutine function
+    // store old pc on stack
+    // set to zero to make op_ret recognizing this as coroutine function
+    cort.ctx.top[0] = var::ret(0);
 
-    cort.ctx.funcr = func; // make sure the coroutine function can use correct upvalues
+    // make sure the coroutine function can use correct upvalues
+    cort.ctx.funcr = func;
     cort.status = nas_co::status::suspended;
     
     return co;
@@ -44,7 +55,10 @@ var builtin_cocreate(var* local, gc& ngc) {
 
 var builtin_coresume(var* local, gc& ngc) {
     if (ngc.cort) {
-        return nas_err("coroutine::resume", "cannot start another coroutine when one is running");
+        return nas_err(
+            "coroutine::resume",
+            "cannot start another coroutine when one is running"
+        );
     }
     var co = local[1];
     // return nil if is not a coroutine object
@@ -61,9 +75,9 @@ var builtin_coresume(var* local, gc& ngc) {
 
     // fetch coroutine's stack top and return
     // so the coroutine's stack top in fact is not changed
-    if (ngc.rctx->top[0].type==vm_ret) {
+    if (ngc.running_context->top[0].type==vm_ret) {
         // when first calling this coroutine, the stack top must be vm_ret
-        return ngc.rctx->top[0];
+        return ngc.running_context->top[0];
     }
 
     // after first calling the coroutine, each time coroutine.yield triggered
diff --git a/src/dylib_lib.cpp b/src/dylib_lib.cpp
index 75c8aee..daae5aa 100644
--- a/src/dylib_lib.cpp
+++ b/src/dylib_lib.cpp
@@ -42,11 +42,11 @@ var builtin_dlopen(var* local, gc& ngc) {
 
 #ifdef _WIN32
     void* func = (void*)GetProcAddress(
-        static_cast<HMODULE>(lib.obj().ptr),
+        static_cast<HMODULE>(lib.obj().pointer),
         "get"
     );
 #else
-    void* func = dlsym(lib.obj().ptr, "get");
+    void* func = dlsym(lib.obj().pointer, "get");
 #endif
     if (!func) {
         return nas_err("dlopen", "cannot find <get> function");
@@ -83,7 +83,7 @@ var builtin_dlcallv(var* local, gc& ngc) {
         return nas_err("dlcall", "\"ptr\" is not a valid function pointer");
     }
     auto& vec = args.vec().elems;
-    return reinterpret_cast<module_func>(fp.obj().ptr)(
+    return reinterpret_cast<module_func>(fp.obj().pointer)(
         vec.data(),
         vec.size(),
         &ngc
@@ -97,9 +97,9 @@ var builtin_dlcall(var* local, gc& ngc) {
     }
 
     var* local_frame_start = local+2;
-    usize local_frame_size = ngc.rctx->top-local_frame_start;
+    usize local_frame_size = ngc.running_context->top-local_frame_start;
     // arguments' stored place begins at local +2
-    return reinterpret_cast<module_func>(fp.obj().ptr)(
+    return reinterpret_cast<module_func>(fp.obj().pointer)(
         local_frame_start,
         local_frame_size,
         &ngc
diff --git a/src/io_lib.cpp b/src/io_lib.cpp
index d057e1e..406ab17 100644
--- a/src/io_lib.cpp
+++ b/src/io_lib.cpp
@@ -92,7 +92,7 @@ var builtin_read(var* local, gc& ngc) {
     if (!buff) {
         return nas_err("read", "malloc failed");
     }
-    f64 res = fread(buff, 1, len.num(), static_cast<FILE*>(fd.obj().ptr));
+    f64 res = fread(buff, 1, len.num(), static_cast<FILE*>(fd.obj().pointer));
     buf.str() = buff;
     buf.val.gcobj->unmut = true;
     delete []buff;
@@ -112,7 +112,7 @@ var builtin_write(var* local, gc& ngc) {
         str.str().c_str(),
         1,
         str.str().length(),
-        static_cast<FILE*>(fd.obj().ptr)
+        static_cast<FILE*>(fd.obj().pointer)
     )));
 }
 
@@ -124,7 +124,7 @@ var builtin_seek(var* local, gc& ngc) {
         return nas_err("seek", "not a valid filehandle");
     }
     return var::num(static_cast<f64>(fseek(
-        static_cast<FILE*>(fd.obj().ptr),
+        static_cast<FILE*>(fd.obj().pointer),
         pos.num(),
         whence.num()
     )));
@@ -135,7 +135,9 @@ var builtin_tell(var* local, gc& ngc) {
     if (!fd.objchk(file_type_name)) {
         return nas_err("tell", "not a valid filehandle");
     }
-    return var::num(static_cast<f64>(ftell(static_cast<FILE*>(fd.obj().ptr))));
+    return var::num(static_cast<f64>(
+        ftell(static_cast<FILE*>(fd.obj().pointer))
+    ));
 }
 
 var builtin_readln(var* local, gc& ngc) {
@@ -145,7 +147,7 @@ var builtin_readln(var* local, gc& ngc) {
     }
     var str = ngc.alloc(vm_str);
     char c;
-    while((c = fgetc(static_cast<FILE*>(fd.obj().ptr)))!=EOF) {
+    while((c = fgetc(static_cast<FILE*>(fd.obj().pointer)))!=EOF) {
         if (c=='\r') {
             continue;
         }
@@ -191,7 +193,9 @@ var builtin_eof(var* local, gc& ngc) {
     if (!fd.objchk(file_type_name)) {
         return nas_err("readln", "not a valid filehandle");
     }
-    return var::num(static_cast<f64>(feof(static_cast<FILE*>(fd.obj().ptr))));
+    return var::num(static_cast<f64>(
+        feof(static_cast<FILE*>(fd.obj().pointer))
+    ));
 }
 
 nasal_builtin_table io_lib_native[] = {
diff --git a/src/nasal_builtin.cpp b/src/nasal_builtin.cpp
index 11fc253..1aacb4c 100644
--- a/src/nasal_builtin.cpp
+++ b/src/nasal_builtin.cpp
@@ -616,7 +616,7 @@ var builtin_ghosttype(var* local, gc& ngc) {
     }
     const auto& name = arg.obj().get_ghost_name();
     if (!name.length()) {
-        return var::num(reinterpret_cast<u64>(arg.obj().ptr));
+        return var::num(reinterpret_cast<u64>(arg.obj().pointer));
     }
     return ngc.newstr(name);
 }
diff --git a/src/nasal_gc.cpp b/src/nasal_gc.cpp
index 193127a..0dda3b8 100644
--- a/src/nasal_gc.cpp
+++ b/src/nasal_gc.cpp
@@ -104,34 +104,34 @@ void nas_ghost::set(
     destructor destructor_pointer,
     void* ghost_pointer) {
     type_name = ghost_type_name;
-    dtor_ptr = destructor_pointer;
-    ptr = ghost_pointer;
+    destructor_function = destructor_pointer;
+    pointer = ghost_pointer;
 }
 
 void nas_ghost::clear() {
     // do nothing if pointer is null
-    if (!ptr) {
+    if (!pointer) {
         return;
     }
 
     // do clear pointer if destructor function pointer is null
-    if (!dtor_ptr) {
+    if (!destructor_function) {
         type_name = "";
-        ptr = nullptr;
+        pointer = nullptr;
         return;
     }
 
     // do destruction
-    dtor_ptr(ptr);
+    destructor_function(pointer);
     type_name = "";
-    ptr = nullptr;
-    dtor_ptr = nullptr;
+    pointer = nullptr;
+    destructor_function = nullptr;
 }
 
 std::ostream& operator<<(std::ostream& out, const nas_ghost& ghost) {
     out << "<object " << ghost.get_ghost_name();
     out << " at 0x" << std::hex;
-    out << reinterpret_cast<u64>(ghost.ptr) << std::dec << ">";
+    out << reinterpret_cast<u64>(ghost.pointer) << std::dec << ">";
     return out;
 }
 
@@ -265,7 +265,7 @@ std::ostream& operator<<(std::ostream& out, var& ref) {
 }
 
 bool var::objchk(const std::string& name) {
-    return type==vm_obj && obj().type_name==name && obj().ptr;
+    return type==vm_obj && obj().type_name==name && obj().pointer;
 }
 
 var var::none() {
@@ -418,13 +418,13 @@ void gc::mark_context_root(std::vector<var>& bfs_queue) {
         }
     }
     // scan now running context, this context maybe related to coroutine or main
-    for(var* i = rctx->stack; i<=rctx->top; ++i) {
+    for(var* i = running_context->stack; i<=running_context->top; ++i) {
         if (i->type>vm_num) {
             bfs_queue.push_back(*i);
         }
     }
-    bfs_queue.push_back(rctx->funcr);
-    bfs_queue.push_back(rctx->upvalr);
+    bfs_queue.push_back(running_context->funcr);
+    bfs_queue.push_back(running_context->upvalr);
     bfs_queue.push_back(temp);
 
     if (!cort) {
@@ -432,13 +432,13 @@ void gc::mark_context_root(std::vector<var>& bfs_queue) {
     }
 
     // coroutine is running, so scan main process stack from mctx
-    for(var* i = mctx.stack; i<=mctx.top; ++i) {
+    for(var* i = main_context.stack; i<=main_context.top; ++i) {
         if (i->type>vm_num) {
             bfs_queue.push_back(*i);
         }
     }
-    bfs_queue.push_back(mctx.funcr);
-    bfs_queue.push_back(mctx.upvalr);
+    bfs_queue.push_back(main_context.funcr);
+    bfs_queue.push_back(main_context.upvalr);
 }
 
 void gc::mark_var(std::vector<var>& bfs_queue, var& value) {
@@ -696,10 +696,10 @@ var gc::alloc(u8 type) {
 
 void gc::ctxchg(nas_co& co) {
     // store running state to main context
-    mctx = *rctx;
+    main_context = *running_context;
 
     // restore coroutine context state
-    *rctx = co.ctx;
+    *running_context = co.ctx;
 
     // set coroutine pointer
     cort = &co;
@@ -710,15 +710,15 @@ void gc::ctxchg(nas_co& co) {
 
 void gc::ctxreserve() {
     // pc=0 means this coroutine is finished
-    cort->status = rctx->pc?
+    cort->status = running_context->pc?
         nas_co::status::suspended:
         nas_co::status::dead;
 
     // store running state to coroutine
-    cort->ctx = *rctx;
+    cort->ctx = *running_context;
 
     // restore main context state
-    *rctx = mctx;
+    *running_context = main_context;
 
     // set coroutine pointer to nullptr
     cort = nullptr;
diff --git a/src/nasal_gc.h b/src/nasal_gc.h
index af6ec61..906700f 100644
--- a/src/nasal_gc.h
+++ b/src/nasal_gc.h
@@ -192,11 +192,12 @@ private:
 
 public:
     std::string type_name;
-    destructor dtor_ptr;
-    void* ptr;
+    destructor destructor_function;
+    void* pointer;
 
 public:
-    nas_ghost(): type_name(""), dtor_ptr(nullptr), ptr(nullptr) {}
+    nas_ghost():
+        type_name(""), destructor_function(nullptr), pointer(nullptr) {}
     ~nas_ghost() {clear();}
     void set(const std::string&, destructor, void*);
     void clear();
@@ -290,14 +291,14 @@ const var nil = var::nil();
 
 struct gc {
     /* main context temporary storage */
-    context mctx;
+    context main_context;
 
     /* global storage */
     var* main_context_global = nullptr;
     usize main_context_global_size = 0;
 
     /* runtime context */
-    context* rctx = nullptr;
+    context* running_context = nullptr;
     nas_co* cort = nullptr; // running coroutine
 
     /*  temporary space used in native/module functions */
@@ -331,7 +332,7 @@ struct gc {
     i64 max_sweep_time = 0;
 
     void set(context* _ctx, var* _global, usize _size) {
-        rctx = _ctx;
+        running_context = _ctx;
         main_context_global = _global;
         main_context_global_size = _size;
     }
@@ -368,13 +369,13 @@ public:
     }
 
     var newstr(const char* buff) {
-        var s=alloc(vm_str);
+        var s = alloc(vm_str);
         s.str() = buff;
         return s;
     }
 
     var newstr(const std::string& buff) {
-        var s=alloc(vm_str);
+        var s = alloc(vm_str);
         s.str() = buff;
         return s;
     }
diff --git a/src/nasal_vm.cpp b/src/nasal_vm.cpp
index c42d6a8..ed16232 100644
--- a/src/nasal_vm.cpp
+++ b/src/nasal_vm.cpp
@@ -93,7 +93,7 @@ void vm::valinfo(var& val) {
                                 << " val}"; break;
         case vm_obj:  std::clog << "| obj  | <0x" << std::hex << p
                                 << "> obj:0x"
-                                << reinterpret_cast<u64>(val.obj().ptr)
+                                << reinterpret_cast<u64>(val.obj().pointer)
                                 << std::dec; break;
         case vm_co:   std::clog << "| co   | <0x" << std::hex << p
                                 << std::dec << "> coroutine"; break;
diff --git a/src/unix_lib.cpp b/src/unix_lib.cpp
index e3ecad2..865384f 100644
--- a/src/unix_lib.cpp
+++ b/src/unix_lib.cpp
@@ -84,12 +84,12 @@ var builtin_readdir(var* local, gc& ngc) {
     }
 #ifdef _MSC_VER
     WIN32_FIND_DATAA data;
-    if (!FindNextFileA(handle.obj().ptr,&data)) {
+    if (!FindNextFileA(handle.obj().pointer, &data)) {
         return nil;
     }
     return ngc.newstr(data.cFileName);
 #else
-    dirent* p = readdir(static_cast<DIR*>(handle.obj().ptr));
+    dirent* p = readdir(static_cast<DIR*>(handle.obj().pointer));
     return p? ngc.newstr(p->d_name):nil;
 #endif
 }