diff --git a/main.cpp b/main.cpp
index 36ad70a..7b806bb 100644
--- a/main.cpp
+++ b/main.cpp
@@ -3,8 +3,8 @@
 nasal_lexer    lexer;
 nasal_parse    parse;
 nasal_import   import;
-std::string    inputfile="null";
-nasal_codegen  code_generator;
+std::string    file="null";
+nasal_codegen  codegen;
 nasal_vm       vm;
 
 void help()
@@ -49,97 +49,51 @@ void clear()
 	return;
 }
 
-void lex_func()
+void execute(std::string& command)
 {
-	lexer.openfile(inputfile);
+	lexer.openfile(file);
 	lexer.scanner();
 	if(lexer.get_error())
 	{
-		die("lexer",inputfile);
+		die("lexer",file);
 		return;
 	}
-	lexer.print_token();
-	clear();
-	return;
-}
-
-void ast_print()
-{
-	lexer.openfile(inputfile);
-	lexer.scanner();
-	if(lexer.get_error())
+	if(command=="lex")
 	{
-		die("lexer",inputfile);
+		lexer.print_token();
+		clear();
 		return;
 	}
 	parse.set_toklist(lexer.get_token_list());
 	parse.main_process();
 	if(parse.get_error())
 	{
-		die("parse",inputfile);
+		die("parse",file);
 		return;
 	}
-	parse.get_root().print_ast(0);
-	clear();
-	return;
-}
-
-void show_bytecode()
-{
-	lexer.openfile(inputfile);
-	lexer.scanner();
-	if(lexer.get_error())
+	if(command=="ast")
 	{
-		die("lexer",inputfile);
-		return;
-	}
-	parse.set_toklist(lexer.get_token_list());
-	parse.main_process();
-	if(parse.get_error())
-	{
-		die("parse",inputfile);
+		parse.get_root().print_ast(0);
+		clear();
 		return;
 	}
 	import.link(parse.get_root());
 	if(import.get_error())
 	{
-		die("import",inputfile);
+		die("import",file);
 		return;
 	}
-	code_generator.main_progress(import.get_root());
+	codegen.main_progress(import.get_root());
 	clear();
-	code_generator.print_byte_code();
-	return;
-}
-
-void execute()
-{
-	lexer.openfile(inputfile);
-	lexer.scanner();
-	if(lexer.get_error())
+	if(command=="code")
 	{
-		die("lexer",inputfile);
+		codegen.print_byte_code();
 		return;
 	}
-	parse.set_toklist(lexer.get_token_list());
-	parse.main_process();
-	if(parse.get_error())
-	{
-		die("parse",inputfile);
-		return;
-	}
-	import.link(parse.get_root());
-	if(import.get_error())
-	{
-		die("import",inputfile);
-		return;
-	}
-	code_generator.main_progress(import.get_root());
-	clear();
 	vm.run(
-		code_generator.get_string_table(),
-		code_generator.get_number_table(),
-		code_generator.get_exec_code()
+		codegen.get_string_table(),
+		codegen.get_number_table(),
+		codegen.get_exec_code()
 	);
 	return;
 }
@@ -175,20 +129,14 @@ int main()
 			system("clear");
 #endif
 		}
-		else if(command=="lex")
-			lex_func();
-		else if(command=="ast")
-			ast_print();
-		else if(command=="code")
-			show_bytecode();
-		else if(command=="exec")
-			execute();
 		else if(command=="logo")
 			logo();
 		else if(command=="exit")
 			break;
+		else if(command=="lex" || command=="ast" || command=="code" || command=="exec")
+			execute(command);
 		else
-			inputfile=command;
+			file=command;
 	}
     return 0;
 }
\ No newline at end of file
diff --git a/nasal_vm.h b/nasal_vm.h
index 8e7b985..692fe10 100644
--- a/nasal_vm.h
+++ b/nasal_vm.h
@@ -885,9 +885,8 @@ void nasal_vm::opr_builtincall()
 void nasal_vm::opr_slicebegin()
 {
     slice_stack.push(gc.gc_alloc(vm_vec));
-    if((*val_stack_top)->get_type()==vm_vec)
-        return;
-    die("slcbegin: must slice a vector");
+    if((*val_stack_top)->get_type()!=vm_vec)
+        die("slcbegin: must slice a vector");
     return;
 }
 void nasal_vm::opr_sliceend()
diff --git a/test/quick_sort.nas b/test/quick_sort.nas
new file mode 100644
index 0000000..9bc78e7
--- /dev/null
+++ b/test/quick_sort.nas
@@ -0,0 +1,32 @@
+import("lib.nas");
+rand(time(0));
+var sort=func(vec,left,right)
+{
+    if(left>=right) return nil;
+    var L=left;
+    var R=right;
+    var tmp=vec[L];
+    while(left<right)
+    {
+        while(left<right and tmp<=vec[right])
+            right-=1;
+        while(left<right and tmp>=vec[left])
+            left+=1;
+        if(left!=right)
+        {
+            var t=vec[left];
+            vec[left]=vec[right];
+            vec[right]=t;
+        }
+    }
+    vec[L]=vec[left];
+    vec[left]=tmp;
+    sort(vec,L,left-1);
+    sort(vec,left+1,R);
+    return nil;
+}
+var vec=[];
+for(var i=0;i<500;i+=1)
+    append(vec,int(rand()*1000));
+sort(vec,0,size(vec)-1);
+println(vec);
\ No newline at end of file