diff --git a/LICENSE b/LICENSE
new file mode 100644
index 0000000..ad646dc
--- /dev/null
+++ b/LICENSE
@@ -0,0 +1,21 @@
+MIT License
+
+Copyright (c) 2017 nae.ikari
+
+Permission is hereby granted, free of charge, to any person obtaining a copy
+of this software and associated documentation files (the "Software"), to deal
+in the Software without restriction, including without limitation the rights
+to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+copies of the Software, and to permit persons to whom the Software is
+furnished to do so, subject to the following conditions:
+
+The above copyright notice and this permission notice shall be included in all
+copies or substantial portions of the Software.
+
+THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE
+SOFTWARE.
diff --git a/lex.c b/lex.c
index b0be8e9..1ba732f 100644
--- a/lex.c
+++ b/lex.c
@@ -101,7 +101,7 @@ int lex_next() {
         if(c >= 0) {
             if(c == '/') {
                 /* "//" comment */
-                while((c = lex_getc()) != '\n') lex_getc();
+                while((c = lex_getc()) != '\n'); lex_getc();
             }
             else if(c == '*') {
                 /* "/*" comment */
diff --git a/test/add1.c b/test/add1.c
new file mode 100644
index 0000000..591f5bc
--- /dev/null
+++ b/test/add1.c
@@ -0,0 +1,3 @@
+int add(int a, int b) {
+    return a + b;
+}
\ No newline at end of file
diff --git a/test/demo/demo.s b/test/demo/demo.s
new file mode 100644
index 0000000..ba2df41
--- /dev/null
+++ b/test/demo/demo.s
@@ -0,0 +1,458 @@
+	 .section	 .rodata
+.S0:
+	 .string "==== Nested Test ====\n"
+.S1:
+	 .string "scope1[a=%d]\n"
+.S2:
+	 .string "scope2[a=%d]\n"
+.S3:
+	 .string "scope3[a=%d]\n"
+.S4:
+	 .string "\n"
+.S5:
+	 .string "=== Expr Test ===\n"
+.S6:
+	 .string "1 * 2 + 3 - (2 * (1 + 2)) = %d. (should be -1)\n\n"
+.S7:
+	 .string "=== Loop Test ===\n"
+.S8:
+	 .string "4 * 5: \n"
+.S9:
+	 .string "    mul_for(4, 5) = %d\n"
+.S10:
+	 .string "  mul_while(4, 5) = %d\n"
+.S11:
+	 .string "           4 * 5  = %d\n"
+.S12:
+	 .string "\n"
+.S13:
+	 .string "=== Recursive Test ===\n"
+.S14:
+	 .string "10! = %d. (should be %d)\n\n"
+	.text
+	 .globl	nested
+	 .type	nested, @function
+nested:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$80, %rsp
+
+	 mov	 $1, %edi
+	 mov	 %edi, -16(%rbp)
+
+	 mov	 $.S0, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -24(%rbp)
+
+	 mov	 $.S1, %rdi
+	 mov	 -16(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -32(%rbp)
+
+	 jmp	.L0
+
+.L0:
+
+	 mov	 $2, %edi
+	 mov	 %edi, -40(%rbp)
+
+	 mov	 $.S2, %rdi
+	 mov	 -40(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -48(%rbp)
+
+	 jmp	.L1
+
+.L1:
+
+	 mov	 $3, %edi
+	 mov	 %edi, -56(%rbp)
+
+	 mov	 $.S3, %rdi
+	 mov	 -56(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -64(%rbp)
+
+	 jmp	.L2
+
+.L2:
+
+	 jmp	.L3
+
+.L3:
+
+	 mov	 $.S4, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -72(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 .globl	expr
+	 .type	expr, @function
+expr:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$56, %rsp
+
+	 mov	 $.S5, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -16(%rbp)
+
+	 mov	 $1, %edi
+	 imull	 $2, %edi
+	 mov	 %edi, -24(%rbp)
+
+	 mov	 -24(%rbp), %edi
+	 add	 $3, %edi
+	 mov	 %edi, -24(%rbp)
+
+	 mov	 $1, %edi
+	 add	 $2, %edi
+	 mov	 %edi, -32(%rbp)
+
+	 mov	 $2, %edi
+	 imull	 -32(%rbp), %edi
+	 mov	 %edi, -40(%rbp)
+
+	 mov	 -24(%rbp), %edi
+	 sub	 -40(%rbp), %edi
+	 mov	 %edi, -24(%rbp)
+
+	 mov	 $.S6, %rdi
+	 mov	 -24(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -48(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 .globl	mul_for
+	 .type	mul_for, @function
+mul_for:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$64, %rsp
+	 mov	%rdi, -16(%rbp)
+	 mov	%rsi, -24(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -40(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -32(%rbp)
+
+.L4:
+
+	 mov	 -32(%rbp), %edi
+	 cmp	 -24(%rbp), %edi
+	 setl	 %al
+	 movzx	 %al, %eax
+	 mov	 %eax, -48(%rbp)
+
+	 cmpl	 $1, -48(%rbp)
+	 je	 .L5
+
+	 jmp	.L6
+
+.L7:
+
+	 mov	 -32(%rbp), %edi
+	 mov	 %edi, -56(%rbp)
+
+	 incl 	 -32(%rbp)
+
+	 jmp	.L4
+
+.L5:
+
+	 mov	 -40(%rbp), %edi
+	 add	 -16(%rbp), %edi
+	 mov	 %edi, -48(%rbp)
+
+	 mov	 -48(%rbp), %edi
+	 mov	 %edi, -40(%rbp)
+
+	 jmp	.L7
+
+.L6:
+
+	 mov	 -40(%rbp), %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 .globl	mul_while
+	 .type	mul_while, @function
+mul_while:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$56, %rsp
+	 mov	%rdi, -16(%rbp)
+	 mov	%rsi, -24(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -32(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -40(%rbp)
+
+.L8:
+
+	 jmp	.L9
+
+.L9:
+
+	 mov	 -32(%rbp), %edi
+	 cmp	 -24(%rbp), %edi
+	 setge	 %al
+	 movzx	 %al, %eax
+	 mov	 %eax, -48(%rbp)
+
+	 cmpl	 $1, -48(%rbp)
+	 je	 .L10
+
+	 jmp	.L11
+
+.L10:
+
+	 jmp	.L12
+
+	 jmp	.L11
+
+.L11:
+
+	 mov	 -40(%rbp), %edi
+	 add	 -16(%rbp), %edi
+	 mov	 %edi, -48(%rbp)
+
+	 mov	 -48(%rbp), %edi
+	 mov	 %edi, -40(%rbp)
+
+	 mov	 -32(%rbp), %edi
+	 mov	 %edi, -48(%rbp)
+
+	 incl 	 -32(%rbp)
+
+	 jmp	.L8
+
+	 mov	 $1234, %edi
+	 mov	 %edi, -40(%rbp)
+
+.L12:
+
+	 mov	 -40(%rbp), %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 .globl	loop
+	 .type	loop, @function
+loop:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$88, %rsp
+
+	 mov	 $.S7, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -16(%rbp)
+
+	 mov	 $.S8, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -24(%rbp)
+
+	 mov	 $4, %rdi
+	 mov	 $5, %rsi
+	 mov $0, %rax
+	 call	mul_for
+	 mov	%eax, -32(%rbp)
+
+	 mov	 $.S9, %rdi
+	 mov	 -32(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -40(%rbp)
+
+	 mov	 $4, %rdi
+	 mov	 $5, %rsi
+	 mov $0, %rax
+	 call	mul_while
+	 mov	%eax, -48(%rbp)
+
+	 mov	 $.S10, %rdi
+	 mov	 -48(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -56(%rbp)
+
+	 mov	 $4, %edi
+	 imull	 $5, %edi
+	 mov	 %edi, -64(%rbp)
+
+	 mov	 $.S11, %rdi
+	 mov	 -64(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -72(%rbp)
+
+	 mov	 $.S12, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -80(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 .globl	fac
+	 .type	fac, @function
+fac:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$48, %rsp
+	 mov	%rdi, -16(%rbp)
+
+	 mov	 -16(%rbp), %edi
+	 cmp	 $1, %edi
+	 sete	 %al
+	 movzx	 %al, %eax
+	 mov	 %eax, -24(%rbp)
+
+	 cmpl	 $1, -24(%rbp)
+	 je	 .L13
+
+	 jmp	.L14
+
+.L13:
+
+	 mov	 $1, %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 jmp	.L15
+
+.L14:
+
+	 mov	 -16(%rbp), %edi
+	 sub	 $1, %edi
+	 mov	 %edi, -24(%rbp)
+
+	 mov	 -24(%rbp), %ebx
+	 mov	 %rbx, %rdi
+	 mov $0, %rax
+	 call	fac
+	 mov	%eax, -32(%rbp)
+
+	 mov	 -32(%rbp), %ebx
+	 mov	 %rbx, %rdi
+	 mov	 -16(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov $0, %rax
+	 call	mul_for
+	 mov	%eax, -40(%rbp)
+
+	 mov	 -40(%rbp), %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+.L15:
+
+	 .globl	recursive
+	 .type	recursive, @function
+recursive:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$40, %rsp
+
+	 mov	 $.S13, %rdi
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -16(%rbp)
+
+	 mov	 $10, %rdi
+	 mov $0, %rax
+	 call	fac
+	 mov	%eax, -24(%rbp)
+
+	 mov	 $.S14, %rdi
+	 mov	 -24(%rbp), %ebx
+	 mov	 %rbx, %rsi
+	 mov	 $3628800, %rdx
+	 mov $0, %rax
+	 call	printf
+	 mov	%eax, -32(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
+	 .globl	main
+	 .type	main, @function
+main:
+	 pushq	%rbp
+	 movq	%rsp, %rbp
+	 subq	$48, %rsp
+
+	 mov $0, %rax
+	 call	nested
+	 mov	%eax, -16(%rbp)
+
+	 mov $0, %rax
+	 call	expr
+	 mov	%eax, -24(%rbp)
+
+	 mov $0, %rax
+	 call	loop
+	 mov	%eax, -32(%rbp)
+
+	 mov $0, %rax
+	 call	recursive
+	 mov	%eax, -40(%rbp)
+
+	 mov	 $0, %edi
+	 mov	 %edi, -8(%rbp)
+
+	 mov	 -8(%rbp), %eax
+	 leave
+	 ret
+
diff --git a/test/demo/redefine.c b/test/demo/redefine.c
new file mode 100644
index 0000000..428173c
--- /dev/null
+++ b/test/demo/redefine.c
@@ -0,0 +1,5 @@
+int main() {
+    int a = 0;
+    int a = 2;
+    return a;
+}
\ No newline at end of file
diff --git a/zcc.h b/zcc.h
index 4f97225..9e21644 100644
--- a/zcc.h
+++ b/zcc.h
@@ -7,7 +7,9 @@ struct type_st;
 struct context_st;
 struct func_st;
 struct var_st;
-union value_un;
+union  value_un;
+struct token_st;
+enum ir_op_en
 
 typedef struct type_st {
     int bytes;
@@ -99,18 +101,11 @@ enum lex_ecode_en {
 };
 
 typedef enum tk_class_en {
-    TK_PLACEHOLDER = 1,
+    TK_NO_CLASS = 0,
     // keywords 
     #define xx(tk_class, u) tk_class,
     #include "keywords.h"
     #undef xx
-    /* 
-    TK_INT = 1,
-    TK_CHAR,
-    TK_VOID,
-    TK_RETURN,
-    TK_CONST,
-    */
     // constant 
     TK_CONST_INT,
     TK_CONST_CHAR,
@@ -152,7 +147,7 @@ extern func_st    *wrap_func;
  
 /* =-- forward declaration --= */
 
-/* lex */
+/* == lex == */
 int lex_load_file(const char *);
 void lex_print_token(token_st *);
 void lex_init();
@@ -163,7 +158,7 @@ int lex_isunaryop(token_st*);
 int lex_isassignop(token_st*);
 int lex_valid();
 
-/* parse */
+/* == parse == */
 void prs_init();
 int prs_expect_char(char);
 int prs_expect_class(tk_class_en);
@@ -192,7 +187,7 @@ int prs_decls();
 int prs_decl();
 type_st* prs_decl_spec();
 
-/* sym */
+/* == sym == */
 int sym_init();
 int sym_hasid(token_st*);
 int sym_hastype(token_st*);
@@ -216,7 +211,7 @@ void        sym_add_type(type_st*);
 label_st*   sym_make_label();
 type_st*    pointer_of(type_st*);
 
-/* gen */
+/* == gen == */
 void gen_emit0(ir_op_en);
 void gen_emit1(ir_op_en, void*);
 void gen_emit2(ir_op_en, void*, void*);
@@ -224,7 +219,9 @@ void gen_emit3(ir_op_en, void*, void*, void*);
 void gen_emit_call(ir_op_en, func_st*, var_st*, list_st*);
 void gen_print_func_ir(func_st*);
 
-/* target-specific gen */
+/* target-specific gen 
+ * link gen-x.c to support different target
+ */
 void gen_assembly(FILE*);
 
 /* util */