diff --git a/nasal_import.h b/nasal_import.h
index 08d8730..984fcf8 100644
--- a/nasal_import.h
+++ b/nasal_import.h
@@ -86,7 +86,7 @@ string linker::findf(const string& fname) {
 
     // we will find lib.nas in nasal std directory
     if (fname=="lib.nas") {
-        return is_windows()? findf("stl\\lib.nas"):findf("stl/lib.nas");
+        return is_windows()? findf("std\\lib.nas"):findf("std/lib.nas");
     }
     if (!show_path) {
         err.err("link", "cannot find file <"+fname+">");
@@ -105,7 +105,7 @@ bool linker::imptchk(const ast& node) {
 /*
     call
     |_id:import
-    |_callh:stl
+    |_callh:std
     |_callh:file
 */
     if (node.type()==ast_call && node[0].str()=="import" && node.size()>=2 && node[1].type()==ast_callh) {
diff --git a/src/nasal_new_codegen.cpp b/src/nasal_new_codegen.cpp
index 1e1f370..a2f7065 100644
--- a/src/nasal_new_codegen.cpp
+++ b/src/nasal_new_codegen.cpp
@@ -237,6 +237,7 @@ void codegen::call_gen(call_expr* node) {
             case expr_type::ast_callh: call_hash_gen((call_hash*)i); break;
             case expr_type::ast_callv: call_vec((call_vector*)i); break;
             case expr_type::ast_callf: call_func((call_function*)i); break;
+            default: break;
         }
     }
 }
@@ -341,6 +342,7 @@ void codegen::mcall(expr* node) {
             case expr_type::ast_callh: call_hash_gen((call_hash*)tmp); break;
             case expr_type::ast_callv: call_vec((call_vector*)tmp); break;
             case expr_type::ast_callf: call_func((call_function*)tmp); break;
+            default: break;
         }
     }
     auto tmp = call_node->get_calls().back();
@@ -444,7 +446,7 @@ void codegen::def_gen(definition_expr* node) {
     node->get_variable_name()? single_def(node):multi_def(node);
 }
 
-void codegen::assignment_gen(assignment_expr* node) {
+void codegen::assignment_expression(assignment_expr* node) {
     switch(node->get_assignment_type()) {
         case assignment_expr::assign_type::equal:
             calc_gen(node->get_right());
@@ -534,7 +536,7 @@ void codegen::assignment_gen(assignment_expr* node) {
     }
 }
 
-void codegen::assign_statement(assignment_expr* node) {
+void codegen::assignment_statement(assignment_expr* node) {
     switch(node->get_assignment_type()) {
         case assignment_expr::assign_type::equal:
             if (node->get_left()->get_type()==expr_type::ast_id) {
@@ -672,6 +674,7 @@ void codegen::loop_gen(expr* node) {
             for_gen((for_expr*)node); break;
         case expr_type::ast_forei:
             forei_gen((forei_expr*)node); break;
+        default: break;
     }
 }
 
@@ -699,7 +702,7 @@ void codegen::while_gen(while_expr* node) {
 }
 
 void codegen::for_gen(for_expr* node) {
-    expr_gen(node->get_initial());
+    statement_generation(node->get_initial());
     usize jmp_place = code.size();
     if (node->get_condition()->get_type()==expr_type::ast_null) {
         regist_num(1);
@@ -712,7 +715,7 @@ void codegen::for_gen(for_expr* node) {
 
     block_gen(node->get_code_block());
     usize continue_place = code.size();
-    expr_gen(node->get_step());
+    statement_generation(node->get_step());
     gen(op_jmp, jmp_place, node->get_step()->get_line());
     code[label_exit].num = code.size();
 
@@ -755,7 +758,7 @@ void codegen::forei_gen(forei_expr* node) {
     gen(op_pop, 0, node->get_line());// pop iterator
 }
 
-void codegen::expr_gen(expr* node) {
+void codegen::statement_generation(expr* node) {
     switch(node->get_type()) {
         case expr_type::ast_null:break;
         case expr_type::ast_def:
@@ -763,17 +766,20 @@ void codegen::expr_gen(expr* node) {
         case expr_type::ast_multi_assign:
             multi_assign_gen((multi_assign*)node); break;
         case expr_type::ast_assign:
-            assign_statement((assignment_expr*)node); break;
+            assignment_statement((assignment_expr*)node); break;
         case expr_type::ast_nil:case expr_type::ast_num:
         case expr_type::ast_str:case expr_type::ast_bool: break;
-        case expr_type::ast_vec:case expr_type::ast_hash:
-        case expr_type::ast_func:case expr_type::ast_call:
+        case expr_type::ast_vec:
+        case expr_type::ast_hash:
+        case expr_type::ast_func:
+        case expr_type::ast_call:
         case expr_type::ast_unary:
         case expr_type::ast_binary:
         case expr_type::ast_ternary:
             calc_gen(node);
             gen(op_pop, 0, node->get_line());
             break;
+        default: break;
     }
 }
 
@@ -956,6 +962,7 @@ void codegen::binary_gen(binary_operator* node) {
                 gen(op_geqc, num_table.at(num), node->get_line());
             }
             return;
+        default: break;
     }
 }
 
@@ -992,7 +999,7 @@ void codegen::calc_gen(expr* node) {
         case expr_type::ast_call:
             call_gen((call_expr*)node); break;
         case expr_type::ast_assign:
-            assignment_gen((assignment_expr*)node); break;
+            assignment_expression((assignment_expr*)node); break;
         case expr_type::ast_ternary:
             trino_gen((ternary_operator*)node); break;
         case expr_type::ast_unary:
@@ -1004,6 +1011,7 @@ void codegen::calc_gen(expr* node) {
             single_def((definition_expr*)node);
             call_id(((definition_expr*)node)->get_variable_name());
             break;
+        default: break;
     }
 }
 
@@ -1032,17 +1040,20 @@ void codegen::block_gen(code_block* node) {
             case expr_type::ast_for:
             case expr_type::ast_forei:
                 loop_gen(tmp); break;
-            case expr_type::ast_binary:
-            case expr_type::ast_vec:case expr_type::ast_hash:
-            case expr_type::ast_func:case expr_type::ast_call:
+            case expr_type::ast_vec:
+            case expr_type::ast_hash:
+            case expr_type::ast_func:
+            case expr_type::ast_call:
             case expr_type::ast_unary:
+            case expr_type::ast_binary:
             case expr_type::ast_ternary:
             case expr_type::ast_def:
             case expr_type::ast_assign:
             case expr_type::ast_multi_assign:
-                expr_gen(tmp); break;
+                statement_generation(tmp); break;
             case expr_type::ast_ret:
                 ret_gen((return_expr*)tmp); break;
+            default: break;
         }
     }
 }
diff --git a/src/nasal_new_codegen.h b/src/nasal_new_codegen.h
index a051e6a..8ef1e7f 100644
--- a/src/nasal_new_codegen.h
+++ b/src/nasal_new_codegen.h
@@ -74,16 +74,16 @@ private:
     void multi_def(definition_expr*);
     void single_def(definition_expr*);
     void def_gen(definition_expr*);
-    void assignment_gen(assignment_expr*);
-    void assign_statement(assignment_expr*);
+    void assignment_expression(assignment_expr*);
+    void assignment_statement(assignment_expr*);
     void multi_assign_gen(multi_assign*);
     void cond_gen(condition_expr*);
     void loop_gen(expr*);
     void load_continue_break(i32, i32);
     void while_gen(while_expr*);
     void for_gen(for_expr*);
-    void expr_gen(expr*);
     void forei_gen(forei_expr*);
+    void statement_generation(expr*);
     void or_gen(binary_operator*);
     void and_gen(binary_operator*);
     void unary_gen(unary_operator*);
diff --git a/src/nasal_new_import.cpp b/src/nasal_new_import.cpp
index da52eb2..00abaff 100644
--- a/src/nasal_new_import.cpp
+++ b/src/nasal_new_import.cpp
@@ -30,7 +30,8 @@ std::string linker::get_path(call_expr* node) {
     return fpath + ".nas";
 }
 
-std::string linker::find_file(const std::string& filename) {
+std::string linker::find_file(
+    const std::string& filename, const span& location) {
     // first add file name itself into the file path
     std::vector<std::string> fpath = {filename};
 
@@ -48,9 +49,12 @@ std::string linker::find_file(const std::string& filename) {
 
     // we will find lib.nas in nasal std directory
     if (filename=="lib.nas") {
-        return is_windows()? find_file("stl\\lib.nas"):find_file("stl/lib.nas");
+        return is_windows()?
+            find_file("std\\lib.nas", location):
+            find_file("std/lib.nas", location);
     }
     if (!show_path) {
+        err.load(location.file);
         err.err("link", "cannot find file <" + filename + ">");
         return "";
     }
@@ -58,6 +62,7 @@ std::string linker::find_file(const std::string& filename) {
     for(const auto& i : fpath) {
         paths += "  " + i + "\n";
     }
+    err.load(location.file);
     err.err("link", "cannot find file <" + filename + "> in these paths:\n" + paths);
     return "";
 }
@@ -66,7 +71,7 @@ bool linker::import_check(expr* node) {
 /*
     call
     |_id:import
-    |_callh:stl
+    |_callh:std
     |_callh:file
 */
     if (node->get_type()!=expr_type::ast_call) {
@@ -149,7 +154,7 @@ code_block* linker::import_regular_file(call_expr* node) {
     node->set_first(new nil_expr(location));
 
     // avoid infinite loading loop
-    filename = find_file(filename);
+    filename = find_file(filename, node->get_location());
     if (!filename.length() || exist(filename)) {
         return new code_block({0, 0, 0, 0, filename});
     }
@@ -166,7 +171,7 @@ code_block* linker::import_regular_file(call_expr* node) {
 code_block* linker::import_nasal_lib() {
     lexer lex(err);
     parse par(err);
-    auto filename = find_file("lib.nas");
+    auto filename = find_file("lib.nas", {0, 0, 0, 0, files[0]});
     if (!filename.length()) {
         return new code_block({0, 0, 0, 0, filename});
     }
diff --git a/src/nasal_new_import.h b/src/nasal_new_import.h
index 09d12b6..73378e5 100644
--- a/src/nasal_new_import.h
+++ b/src/nasal_new_import.h
@@ -29,7 +29,7 @@ private:
     bool exist(const std::string&);
     void link(code_block*, code_block*);
     std::string get_path(call_expr*);
-    std::string find_file(const std::string&);
+    std::string find_file(const std::string&, const span&);
     code_block* import_regular_file(call_expr*);
     code_block* import_nasal_lib();
     code_block* load(code_block*, u16);
diff --git a/src/nasal_new_main.cpp b/src/nasal_new_main.cpp
index c0de3e7..ae6efff 100644
--- a/src/nasal_new_main.cpp
+++ b/src/nasal_new_main.cpp
@@ -80,6 +80,7 @@ std::ostream& version(std::ostream& out) {
     }
     out << "version " << __nasver;
     out << " (" << __DATE__ << " " << __TIME__ << ")\n";
+    return out;
 }
 
 [[noreturn]]
diff --git a/stl/csv.nas b/std/csv.nas
similarity index 100%
rename from stl/csv.nas
rename to std/csv.nas
diff --git a/stl/fg_env.nas b/std/fg_env.nas
similarity index 100%
rename from stl/fg_env.nas
rename to std/fg_env.nas
diff --git a/stl/file.nas b/std/file.nas
similarity index 100%
rename from stl/file.nas
rename to std/file.nas
diff --git a/stl/json.nas b/std/json.nas
similarity index 100%
rename from stl/json.nas
rename to std/json.nas
diff --git a/stl/lib.nas b/std/lib.nas
similarity index 100%
rename from stl/lib.nas
rename to std/lib.nas
diff --git a/stl/list.nas b/std/list.nas
similarity index 100%
rename from stl/list.nas
rename to std/list.nas
diff --git a/stl/log.nas b/std/log.nas
similarity index 100%
rename from stl/log.nas
rename to std/log.nas
diff --git a/stl/mat.nas b/std/mat.nas
similarity index 100%
rename from stl/mat.nas
rename to std/mat.nas
diff --git a/stl/module.nas b/std/module.nas
similarity index 100%
rename from stl/module.nas
rename to std/module.nas
diff --git a/stl/padding.nas b/std/padding.nas
similarity index 100%
rename from stl/padding.nas
rename to std/padding.nas
diff --git a/stl/process_bar.nas b/std/process_bar.nas
similarity index 100%
rename from stl/process_bar.nas
rename to std/process_bar.nas
diff --git a/stl/queue.nas b/std/queue.nas
similarity index 100%
rename from stl/queue.nas
rename to std/queue.nas
diff --git a/stl/result.nas b/std/result.nas
similarity index 100%
rename from stl/result.nas
rename to std/result.nas
diff --git a/stl/sort.nas b/std/sort.nas
similarity index 100%
rename from stl/sort.nas
rename to std/sort.nas
diff --git a/stl/stack.nas b/std/stack.nas
similarity index 100%
rename from stl/stack.nas
rename to std/stack.nas
diff --git a/stl/string.nas b/std/string.nas
similarity index 100%
rename from stl/string.nas
rename to std/string.nas
diff --git a/test/ascii-art.nas b/test/ascii-art.nas
index e1cf805..08c29fd 100644
--- a/test/ascii-art.nas
+++ b/test/ascii-art.nas
@@ -1,5 +1,5 @@
-import.stl.padding;
-import.stl.process_bar;
+import.std.padding;
+import.std.process_bar;
 
 var char_ttf=[
     ["    ","    ","    ","    ","    ","    "],
diff --git a/test/auto_crash.nas b/test/auto_crash.nas
index 2ab0e72..cd5dce7 100644
--- a/test/auto_crash.nas
+++ b/test/auto_crash.nas
@@ -1,5 +1,5 @@
 # Road check and auto pilot by ValKmjolnir
-import.stl.fg_env;
+import.std.fg_env;
 
 var dt=0.01;
 var intergral=0;
diff --git a/test/bfs.nas b/test/bfs.nas
index b210665..dffce5b 100644
--- a/test/bfs.nas
+++ b/test/bfs.nas
@@ -1,4 +1,4 @@
-import.stl.queue;
+import.std.queue;
 
 rand(time(0));
 var pixel=[' ','#','.','*'];
diff --git a/test/bp.nas b/test/bp.nas
index 47b1438..1218a2d 100644
--- a/test/bp.nas
+++ b/test/bp.nas
@@ -1,4 +1,4 @@
-import.stl.mat;
+import.std.mat;
 
 rand(time(0));
 
diff --git a/test/calc.nas b/test/calc.nas
index c322450..a14692e 100644
--- a/test/calc.nas
+++ b/test/calc.nas
@@ -1,11 +1,11 @@
-import.stl.padding;
-import.stl.file;
-import.stl.sort;
+import.std.padding;
+import.std.file;
+import.std.sort;
 
 var source=find_all_files_with_extension(".","cpp","h");
 sort(source,func(a,b){return cmp(a,b)<0});
 
-var lib=find_all_files_with_extension("./stl","nas");
+var lib=find_all_files_with_extension("./std","nas");
 sort(lib,func(a,b){return cmp(a,b)<0});
 
 var testfile=find_all_files_with_extension("./test","nas");
@@ -79,7 +79,7 @@ var calc=func(codetype,files,path=""){
 }
 
 var all=calc("source code:",source)
-    +calc("lib:",lib,"stl/")
+    +calc("lib:",lib,"std/")
     +calc("test file:",testfile,"test/")
     +calc("module:",module,"module/");
 println(rightpad("total:",padding_length),'|',leftpad(str(all),6),' kb   |');
\ No newline at end of file
diff --git a/test/coroutine.nas b/test/coroutine.nas
index 20e1732..0e2e8b9 100644
--- a/test/coroutine.nas
+++ b/test/coroutine.nas
@@ -1,7 +1,7 @@
 # coroutine.nas by ValKmjolnir
 # 2022/5/19
-import.stl.process_bar;
-import.stl.padding;
+import.std.process_bar;
+import.std.padding;
 
 if(os.platform()=="windows"){
     system("chcp 65001");
diff --git a/test/datalog.nas b/test/datalog.nas
index 2c5560c..31af9ea 100644
--- a/test/datalog.nas
+++ b/test/datalog.nas
@@ -1,6 +1,6 @@
-import.stl.sort;
-import.stl.padding;
-import.stl.process_bar;
+import.std.sort;
+import.std.padding;
+import.std.process_bar;
 
 var mess=func(vec) {
     srand();
diff --git a/test/json.nas b/test/json.nas
index 990a255..5355d92 100644
--- a/test/json.nas
+++ b/test/json.nas
@@ -1,5 +1,5 @@
-import.stl.json;
-import.stl.process_bar;
+import.std.json;
+import.std.process_bar;
 
 var ss=JSON.stringify({
     vec:[0,1,2],
diff --git a/test/jsonrpc.nas b/test/jsonrpc.nas
index d4f5e0d..37ef20e 100644
--- a/test/jsonrpc.nas
+++ b/test/jsonrpc.nas
@@ -1,5 +1,5 @@
 import.module.libsock;
-import.stl.json;
+import.std.json;
 
 var gettime=func(){
     return split(" ",os.time())[1];
diff --git a/test/lexer.nas b/test/lexer.nas
index c8410a6..561eb57 100644
--- a/test/lexer.nas
+++ b/test/lexer.nas
@@ -172,7 +172,7 @@ var lexer=func(file)
     };
 }
 
-var lex=lexer("stl/fg_env.nas");
+var lex=lexer("std/fg_env.nas");
 lex.compile();
 foreach(var tok;lex.get_token())
     print('(',tok.line,' | ',tok.token,')\n');
\ No newline at end of file
diff --git a/test/life.nas b/test/life.nas
index bffbf7a..3978352 100644
--- a/test/life.nas
+++ b/test/life.nas
@@ -1,4 +1,4 @@
-import.stl.process_bar;
+import.std.process_bar;
 
 var new_map=func(width,height){
     var tmp=[];
diff --git a/test/md5compare.nas b/test/md5compare.nas
index 8f980d5..a6e9566 100644
--- a/test/md5compare.nas
+++ b/test/md5compare.nas
@@ -1,6 +1,6 @@
 import.test.md5;
-import.stl.process_bar;
-import.stl.file;
+import.std.process_bar;
+import.std.file;
 srand();
 
 var compare=func() {
@@ -48,8 +48,8 @@ var filechecksum=func(){
     foreach(var p;find_all_files_with_extension("./test","nas")) {
         append(files,"./test/"~p);
     }
-    foreach(var p;find_all_files_with_extension("./stl","nas")) {
-        append(files,"./stl/"~p);
+    foreach(var p;find_all_files_with_extension("./std","nas")) {
+        append(files,"./std/"~p);
     }
     foreach(var p;find_all_files_with_extension("./module","nas","cpp")) {
         append(files,"./module/"~p);
diff --git a/test/occupation.nas b/test/occupation.nas
index b527e15..b46fe76 100644
--- a/test/occupation.nas
+++ b/test/occupation.nas
@@ -1,4 +1,4 @@
-import.stl.process_bar;
+import.std.process_bar;
 import.module.libkey;
 
 var is_windows_platform=os.platform()=="windows";
diff --git a/test/ppmgen.nas b/test/ppmgen.nas
index 8de5a3d..75e725d 100644
--- a/test/ppmgen.nas
+++ b/test/ppmgen.nas
@@ -1,4 +1,4 @@
-import.stl.process_bar;
+import.std.process_bar;
 
 var ppm=func(filename,width,height,RGB){
     # P3 use ASCII number
diff --git a/test/quick_sort.nas b/test/quick_sort.nas
index 1456fe0..21b6438 100644
--- a/test/quick_sort.nas
+++ b/test/quick_sort.nas
@@ -1,4 +1,4 @@
-import.stl.sort;
+import.std.sort;
 
 var vec=[];
 rand(time(0));
diff --git a/test/word_collector.nas b/test/word_collector.nas
index e033cdd..23efb73 100644
--- a/test/word_collector.nas
+++ b/test/word_collector.nas
@@ -1,4 +1,4 @@
-import.stl.sort;
+import.std.sort;
 
 var to_lower=func(s){
     var tmp="";