diff --git a/README.md b/README.md
index 4112965..28e1518 100644
--- a/README.md
+++ b/README.md
@@ -774,3 +774,56 @@ nasal_val* builtin_keys(std::vector<nasal_val*>& local_scope,nasal_gc& gc)
     return ret_addr;
 }
 ```
+
+## Difference Between Andy's Nasal Interpreter and This Interpreter
+
+This interpreter uses more strict syntax to make sure it is easier for you to program and debug.
+
+In Andy's interpreter:
+
+```javascript
+foreach(i;[0,1,2,3])
+    print(i)
+```
+
+This program can run normally with output 0 1 2 3.
+But take a look at the iterator 'i',this symbol is defined in foreach without using keyword 'var'.
+I think this design will make programmers filling confused.
+This is ambiguous that programmers maybe difficult to find the 'i' is defined here.
+Without 'var',programmers may think this 'i' is defined anywhere else.
+
+So in this new interpreter i use a more strict syntax to force users to use 'var' to define iterator of forindex and foreach.
+If you forget to add the keyword 'var', and you haven't defined this symbol before, you will get this:
+
+```javascript
+>> [code] line 1: undefined symbol "i".
+>> [codegen] in <"test.nas">: error(s) occurred,stop.
+```
+
+Also there's another difference.
+In Andy's interpreter:
+
+```javascript
+var a=func {print(b);}
+var b=1;
+a();
+```
+
+This program runs normally with output 1.
+But in this new interpreter, it will get:
+
+```javascript
+>> [code] line 1: undefined symbol "b".
+>> [codegen] in <"test.nas">: error(s) occurred,stop.
+```
+
+This difference is caused by different kinds of ways of lexical analysis.
+In most script language interpreters, they use dynamic analysis to check if this symbol is defined yet.
+However, this kind of analysis is at the cost of lower efficiency.
+To make sure the interpreter runs at higher efficiency, i choose static analysis to manage the memory space of each symbol.
+By this way, runtime will never need to check if a symbol exists or not.
+But this causes a difference.
+You will get an error of 'undefined symbol', instead of nothing happening in most script language interpreters.
+
+This change is __controversial__ among FGPRC's members.
+So maybe in the future i will use dynamic analysis again to cater to the habits of senior programmers.
diff --git a/main.cpp b/main.cpp
index 497003f..0e751a2 100644
--- a/main.cpp
+++ b/main.cpp
@@ -18,20 +18,23 @@ void help_cmd()
 #ifdef _WIN32
 	<<"use command \'chcp 65001\' if want to use unicode.\n"
 #endif
-	<<"nasal               | use interactive interpreter.\n"
-	<<"nasal -h, --help    | get help.\n"
-	<<"nasal -v, --version | get version of nasal interpreter.\n"
-	<<"nasal filename      | execute script file.\n";
+	<<"nasal [option]|[file]\n"
+	<<"    input 0 argument to use the interactive interpreter.\n"
+	<<"option:\n"
+	<<"    -h, --help    | get help.\n"
+	<<"    -v, --version | get version of nasal interpreter.\n"
+	<<"file:\n"
+	<<"    input file name to execute script file.\n";
 	return;
 }
 void info()
 {
 	std::cout
-	<<">> Thanks to https://github.com/andyross/nasal\n"
-	<<">> Code: https://github.com/ValKmjolnir/Nasal-Interpreter\n"
-	<<">> Code: https://gitee.com/valkmjolnir/Nasal-Interpreter\n"
-	<<">> Info: http://wiki.flightgear.org/Nasal_scripting_language\n"
-	<<">> Input \"help\" to get help .\n";
+	<<">> thanks to https://github.com/andyross/nasal\n"
+	<<">> code: https://github.com/ValKmjolnir/Nasal-Interpreter\n"
+	<<">> code: https://gitee.com/valkmjolnir/Nasal-Interpreter\n"
+	<<">> info: http://wiki.flightgear.org/Nasal_scripting_language\n"
+	<<">> input \"help\" to get help .\n";
 	return;
 }
 void logo()
@@ -42,7 +45,7 @@ void logo()
 	<<"   /  \\/ / _` / __|/ _` | |    \n"
 	<<"  / /\\  / (_| \\__ \\ (_| | |  \n"
 	<<"  \\_\\ \\/ \\__,_|___/\\__,_|_|\n"
-	<<"   Nasal interpreter ver 7.0    \n";
+	<<"   nasal interpreter ver 7.0    \n";
     return;
 }
 void die(const char* stage,std::string& filename)
diff --git a/nasal_ast.h b/nasal_ast.h
index 6416488..fad32f2 100644
--- a/nasal_ast.h
+++ b/nasal_ast.h
@@ -80,8 +80,8 @@ nasal_ast::nasal_ast(const nasal_ast& tmp)
 {
     line=tmp.line;
     type=tmp.type;
-    str =tmp.str;
     num =tmp.num;
+    str =tmp.str;
     children=tmp.children;
     return;
 }
@@ -90,8 +90,8 @@ nasal_ast::nasal_ast(nasal_ast&& tmp)
 {
     line=tmp.line;
     type=tmp.type;
-    str.swap(tmp.str);
     num =tmp.num;
+    str.swap(tmp.str);
     children.swap(tmp.children);
     return;
 }
@@ -100,8 +100,8 @@ nasal_ast& nasal_ast::operator=(const nasal_ast& tmp)
 {
     line=tmp.line;
     type=tmp.type;
-    str=tmp.str;
     num=tmp.num;
+    str=tmp.str;
     children=tmp.children;
     return *this;
 }
@@ -110,8 +110,8 @@ nasal_ast& nasal_ast::operator=(nasal_ast&& tmp)
 {
     line=tmp.line;
     type=tmp.type;
-    str.swap(tmp.str);
     num=tmp.num;
+    str.swap(tmp.str);
     children.swap(tmp.children);
     return *this;
 }
@@ -119,8 +119,8 @@ nasal_ast& nasal_ast::operator=(nasal_ast&& tmp)
 void nasal_ast::clear()
 {
     line=0;
-    str="";
     num=0;
+    str="";
     type=ast_null;
     children.clear();
     return;