diff --git a/lib.nas b/lib.nas
index 8822adc..77fa6a1 100644
--- a/lib.nas
+++ b/lib.nas
@@ -100,6 +100,8 @@ var unix=
     dup2:     func(fd0,fd1){die("not supported yet");},
     exec:     func(filename,argv,envp){die("not supported yet");},
     waitpid:  func(pid,nohang=0){die("not supported yet");},
+    isdir:    func(path){return bits.bitand(io.stat(path)[2],0x4000);}, # S_IFDIR 0x4000
+    isfile:   func(path){return bits.bitand(io.stat(path)[2],0x8000);}, # S_IFREG 0x8000
     opendir:  func(path){return __builtin_opendir;},
     readdir:  func(handle){return __builtin_readdir;},
     closedir: func(handle){return __builtin_closedir;},
diff --git a/nasal_codegen.h b/nasal_codegen.h
index 64a28fb..303de81 100644
--- a/nasal_codegen.h
+++ b/nasal_codegen.h
@@ -1231,7 +1231,7 @@ void nasal_codegen::print_op(uint32_t index)
         case op_addeqc:case op_subeqc: case op_muleqc:case op_diveqc:
         case op_lessc: case op_leqc:   case op_grtc:  case op_geqc:
         case op_pnum:
-            printf("0x%x (%lf)\n",c.num,num_res[c.num]);break;
+            printf("0x%x (",c.num);std::cout<<num_res[c.num]<<")\n";break;
         case op_callvi:case op_newv:   case op_callfv:
         case op_intg:  case op_intl:
         case op_newf:  case op_jmp:    case op_jt:    case op_jf:
diff --git a/nasal_gc.h b/nasal_gc.h
index 4e8ddcd..89f52f1 100644
--- a/nasal_gc.h
+++ b/nasal_gc.h
@@ -307,7 +307,7 @@ inline nasal_hash*  nasal_ref::hash(){return value.gcobj->ptr.hash;}
 inline nasal_func*  nasal_ref::func(){return value.gcobj->ptr.func;}
 inline nasal_obj*   nasal_ref::obj (){return value.gcobj->ptr.obj; }
 
-constexpr uint32_t STACK_MAX_DEPTH=2047;
+constexpr uint32_t STACK_MAX_DEPTH=4095;
 struct nasal_gc
 {
     nasal_ref               zero;
diff --git a/nasal_vm.h b/nasal_vm.h
index 97fefeb..b6c59aa 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -188,7 +188,7 @@ void nasal_vm::traceback()
     if(same)
         printf("\t0x%.8x: %d same call(s) ...\n",last,same);
 }
-void nasal_vm::stackinfo(const uint32_t limit=10)
+void nasal_vm::stackinfo(const uint32_t limit=20)
 {
     printf("vm stack(limit %d):\n",limit);
     uint32_t same=0,global_size=bytecode[0].num;
@@ -327,7 +327,7 @@ inline void nasal_vm::opr_pzero()
 }
 inline void nasal_vm::opr_pnil()
 {
-    (++gc.top)[0].type=vm_nil;
+    (++gc.top)[0]={vm_nil,(double)0};
 }
 inline void nasal_vm::opr_pstr()
 {
@@ -394,7 +394,7 @@ inline void nasal_vm::opr_unot()
         {
             double num=str2num(val.str()->c_str());
             if(std::isnan(num))
-                gc.top[0]=val.str()->empty()?gc.one:gc.zero;
+                gc.top[0]={vm_num,(double)val.str()->empty()};
             else
                 gc.top[0]=num?gc.zero:gc.one;
         }
diff --git a/stl/lib.nas b/stl/lib.nas
index 8822adc..77fa6a1 100644
--- a/stl/lib.nas
+++ b/stl/lib.nas
@@ -100,6 +100,8 @@ var unix=
     dup2:     func(fd0,fd1){die("not supported yet");},
     exec:     func(filename,argv,envp){die("not supported yet");},
     waitpid:  func(pid,nohang=0){die("not supported yet");},
+    isdir:    func(path){return bits.bitand(io.stat(path)[2],0x4000);}, # S_IFDIR 0x4000
+    isfile:   func(path){return bits.bitand(io.stat(path)[2],0x8000);}, # S_IFREG 0x8000
     opendir:  func(path){return __builtin_opendir;},
     readdir:  func(handle){return __builtin_readdir;},
     closedir: func(handle){return __builtin_closedir;},
diff --git a/test/filesystem.nas b/test/filesystem.nas
index e074894..f244dc0 100644
--- a/test/filesystem.nas
+++ b/test/filesystem.nas
@@ -7,6 +7,30 @@ io.close(fd);
 println(io.stat("test/filesystem.nas"));
 
 var dd=unix.opendir("test");
-while((var name=unix.readdir(dd))!=nil)
+while(var name=unix.readdir(dd))
     println(name);
-unix.closedir(dd);
\ No newline at end of file
+unix.closedir(dd);
+
+var files=func(dir){
+    var dd=unix.opendir(dir);
+    var res=[];
+    while(var n=unix.readdir(dd))
+        append(res,n);
+    unix.closedir(dd);
+    return res;
+}
+var prt=func(s,path){
+    foreach(var i;files(path)){
+        print(s,i);
+        if(unix.isdir(path~'/'~i)){
+            print(' <dir>\n');
+            if(i!='.' and i!='..')
+                prt(s~' |',path~'/'~i);
+        }
+        elsif(unix.isfile(path~'/'~i))
+            print(" <file>\n");
+        else
+            print(' <unknown>\n');
+    }
+}
+prt('',".");
\ No newline at end of file