diff --git a/lib.nas b/lib.nas
index fa46b87..2c5c070 100644
--- a/lib.nas
+++ b/lib.nas
@@ -90,6 +90,10 @@ var type=func(object)
 {
     return nasal_call_builtin_type(object);
 }
+var substr=func(str,begin,length)
+{
+    return nasal_call_builtin_substr(str,begin,length);
+}
 
 var io=
 {
diff --git a/nasal_builtin.h b/nasal_builtin.h
index 3b7011c..e71a2ac 100644
--- a/nasal_builtin.h
+++ b/nasal_builtin.h
@@ -267,18 +267,27 @@ int nasal_runtime::builtin_split(int local_scope_addr)
     std::string delimeter=nasal_vm.gc_get(delimeter_value_addr).get_string();
     std::string source=nasal_vm.gc_get(string_value_addr).get_string();
     int delimeter_len=delimeter.length();
-    if(delimeter_len<1)
-    {
-        std::cout<<">> [runtime] builtin_split: delimeter's length must be greater than 0.\n";
-        ++error;
-        return -1;
-    }
     int source_len=source.length();
 
     int ret_addr=nasal_vm.gc_alloc();
     nasal_vm.gc_get(ret_addr).set_type(vm_vector);
     nasal_vector& ref_vec=nasal_vm.gc_get(ret_addr).get_vector();
     std::string tmp="";
+
+    if(!delimeter_len)
+    {
+        for(int i=0;i<source_len;++i)
+        {
+            tmp+=source[i];
+            int str_addr=nasal_vm.gc_alloc();
+            nasal_vm.gc_get(str_addr).set_type(vm_string);
+            nasal_vm.gc_get(str_addr).set_string(tmp);
+            ref_vec.add_elem(str_addr);
+            tmp="";
+        }
+        return ret_addr;
+    }
+    
     for(int i=0;i<source_len;++i)
     {
         bool check_delimeter=false;
@@ -786,4 +795,44 @@ int nasal_runtime::builtin_type(int local_scope_addr)
     }
     return ret_addr;
 }
+int nasal_runtime::builtin_substr(int local_scope_addr)
+{
+    int str_addr=in_builtin_find("str");
+    int begin_addr=in_builtin_find("begin");
+    int length_addr=in_builtin_find("length");
+    if(str_addr<0 || !in_builtin_check(str_addr,vm_string))
+    {
+        std::cout<<">> [runtime] builtin_substr: cannot find \"str\" or wrong type(must be string).\n";
+        ++error;
+        return -1;
+    }
+    if(begin_addr<0 || !in_builtin_check(begin_addr,vm_number))
+    {
+        std::cout<<">> [runtime] builtin_substr: cannot find \"begin\" or wrong type(must be number).\n";
+        ++error;
+        return -1;
+    }
+    if(length_addr<0 || !in_builtin_check(length_addr,vm_number))
+    {
+        std::cout<<">> [runtime] builtin_substr: cannot find \"length\" or wrong type(must be number).\n";
+        ++error;
+        return -1;
+    }
+    std::string str=nasal_vm.gc_get(str_addr).get_string();
+    int begin=(int)nasal_vm.gc_get(begin_addr).get_number();
+    int len=(int)nasal_vm.gc_get(length_addr).get_number();
+    if(begin>=str.length() || begin+len>=str.length())
+    {
+        std::cout<<">> [runtime] builtin_substr: index out of range.\n";
+        ++error;
+        return -1;
+    }
+    std::string tmp="";
+    for(int i=begin;i<begin+len;++i)
+        tmp+=str[i];
+    int ret_addr=nasal_vm.gc_alloc();
+    nasal_vm.gc_get(ret_addr).set_type(vm_string);
+    nasal_vm.gc_get(ret_addr).set_string(tmp);
+    return ret_addr;
+}
 #endif
\ No newline at end of file
diff --git a/nasal_runtime.h b/nasal_runtime.h
index 04e3e9e..d093784 100644
--- a/nasal_runtime.h
+++ b/nasal_runtime.h
@@ -102,6 +102,7 @@ private:
     int builtin_import(int);
     int builtin_die(int);
     int builtin_type(int);
+    int builtin_substr(int);
     void load_builtin_function();
 public:
     nasal_runtime();
@@ -169,6 +170,7 @@ void nasal_runtime::load_builtin_function()
         {"nasal_call_import",                nasal_runtime::builtin_import},
         {"nasal_call_builtin_die",           nasal_runtime::builtin_die},
         {"nasal_call_builtin_type",          nasal_runtime::builtin_type},
+        {"nasal_call_builtin_substr",        nasal_runtime::builtin_substr},
         {"",                                 NULL}
     };
     for(int i=0;builtin_func_table[i].func_pointer;++i)
diff --git a/test/lexer.nas b/test/lexer.nas
new file mode 100644
index 0000000..e57c5be
--- /dev/null
+++ b/test/lexer.nas
@@ -0,0 +1,171 @@
+import("lib.nas");
+
+var s=io.fin("lexer.nas");
+s=split('',s);
+var len=size(s);
+var ptr=0;
+
+var cmp=func(s1,s2)
+{
+    var size1=size(s1);
+    var size2=size(s2);
+    if(size1!=size2)
+        return size1<size2;
+    for(var i=0;i<size1;i+=1)
+        if(s1[i]>s2[i])
+            return 0;
+    return 1;
+}
+
+var jump_note=func()
+{
+    while(ptr<len and s[ptr]!='\n')
+        ptr+=1;
+    ptr+=1;
+    return;
+}
+
+var generate_id=func()
+{
+    var tmp="";
+    while(ptr<len)
+    {
+        if('a'[0]<=s[ptr][0] and s[ptr][0]<='z'[0]
+        or 'A'[0]<=s[ptr][0] and s[ptr][0]<='Z'[0]
+        or s[ptr]=='_'
+        or '0'[0]<=s[ptr][0] and s[ptr][0]<='9'[0])
+            tmp~=s[ptr];
+        else
+            break;
+        ptr+=1;
+    }
+    return tmp;
+}
+
+var generate_str=func()
+{
+    var tok_str="";
+    var mark=s[ptr];
+    ptr+=1;
+    while(ptr<len and s[ptr]!=mark)
+    {
+        if(s[ptr]=='\\')
+        {
+            ptr+=1;
+            if(s[ptr]=='a') tok_str~='\a';
+            elsif(s[ptr]=='b') tok_str~='\b';
+            elsif(s[ptr]=='f') tok_str~='\f';
+            elsif(s[ptr]=='n') tok_str~='\n';
+            elsif(s[ptr]=='r') tok_str~='\r';
+            elsif(s[ptr]=='t') tok_str~='\t';
+            elsif(s[ptr]=='v') tok_str~='\v';
+            elsif(s[ptr]=='?') tok_str~='?';
+            elsif(s[ptr]=='0') tok_str~='\0';
+            elsif(s[ptr]=='\\') tok_str~='\\';
+            elsif(s[ptr]=='\'') tok_str~='\'';
+            elsif(s[ptr]=='\"') tok_str~='\"';
+            else tok_str~=s[ptr];
+        }
+        else
+            tok_str~=s[ptr];
+        ptr+=1;
+    }
+    if(ptr>=len)
+    {
+        print("read eof when generating string.");
+        break;
+    }
+    ptr+=1;
+    return tok_str;
+}
+
+var generate_number=func()
+{
+    var number=s[ptr];
+    ptr+=1;
+    if(s[ptr]=='x')
+    {
+        ptr+=1;
+        while(ptr<len and ('a'[0]<=s[ptr][0] and s[ptr][0]<='f'[0] or '0'[0]<=s[ptr][0] and s[ptr][0]<='9'[0]))
+        {
+            number~=s[ptr];
+            ptr+=1;
+        }
+        return num(number);
+    }
+    elsif(s[ptr]=='o')
+    {
+        ptr+=1;
+        while(ptr<len and ('0'[0]<=s[ptr][0] and s[ptr][0]<='7'[0]))
+        {
+            number~=s[ptr];
+            ptr+=1;
+        }
+        return num(number);
+    }
+
+    while(ptr<len and ('0'[0]<=s[ptr][0] and s[ptr][0]<='9'[0]))
+    {
+        number~=s[ptr];
+        ptr+=1;
+    }
+    if(s[ptr]=='.')
+        number~=s[ptr];
+    else
+        return num(number);
+    return num(number);
+}
+
+var generate_operator=func()
+{
+    var tmp="";
+    if(s[ptr]=='+' or s[ptr]=='-' or s[ptr]=='~' or s[ptr]=='/' or s[ptr]=='*' or s[ptr]=='>' or s[ptr]=='<' or s[ptr]=='!' or s[ptr]=='=')
+    {
+        tmp=s[ptr];
+        ptr+=1;
+        if(ptr<len and s[ptr]=='=')
+        {
+            tmp~=s[ptr];
+            ptr+=1;
+        }
+        return tmp;
+    }
+    elsif(s[ptr]=='.')
+    {
+        if(ptr+2<len and s[ptr+1]=='.' and s[ptr+2]=='.')
+        {
+            tmp='...';
+            ptr+=3;
+        }
+        else
+        {
+            tmp='.';
+            ptr+=1;
+        }
+        return tmp;
+    }
+    elsif(s[ptr]!=' ' and s[ptr]!='\t' and s[ptr]!='\n' and s[ptr]!='\r' and s[ptr][0]>0)
+        tmp=s[ptr];
+    ptr+=1;
+    return tmp;
+}
+var cnt=0;
+while(ptr<len)
+{
+    if(s[ptr]=='#')
+        jump_note();
+    elsif('a'[0]<=s[ptr][0] and s[ptr][0]<='z'[0] or 'A'[0]<=s[ptr][0] and s[ptr][0]<='Z'[0] or s[ptr]=='_')
+        print("(",cnt+=1," | ",generate_id(),")");
+    elsif(s[ptr]=='\'' or s[ptr]=='\"')
+        print("(",cnt+=1," | \"",generate_str(),"\")");
+    elsif('0'[0]<=s[ptr][0] and s[ptr][0]<='9'[0])
+        print("(",cnt+=1," | ",generate_number(),")");
+    else
+    {
+        var tmp=generate_operator();
+        if(size(tmp))
+            print("(",cnt+=1," | ",tmp,")");
+    }
+    if(ptr>=len)
+        break;
+}
\ No newline at end of file