remove tab characters

Author: lotabout

tutorial/en/2-Virtual-Machine.md

@@ -319,37 +319,37 @@ int callee(int, int, int);
 
 int caller(void)
 {
-	int i, ret;
+        int i, ret;
 
-	ret = callee(1, 2, 3);
-	ret += 5;
-	return ret;
+        ret = callee(1, 2, 3);
+        ret += 5;
+        return ret;
 }
 ```
 
 The compiler will generate the following assembly instructions:
 
 ```
 caller:
-	; make new call frame
-	push    ebp
-	mov     ebp, esp
+        ; make new call frame
+        push    ebp
+        mov     ebp, esp
         sub     1, esp       ; save stack for variable: i
-	; push call arguments
-	push    3
-	push    2
-	push    1
-	; call subroutine 'callee'
-	call    callee
-	; remove arguments from frame
-	add     esp, 12
-	; use subroutine result
-	add     eax, 5
-	; restore old call frame
+        ; push call arguments
+        push    3
+        push    2
+        push    1
+        ; call subroutine 'callee'
+        call    callee
+        ; remove arguments from frame
+        add     esp, 12
+        ; use subroutine result
+        add     eax, 5
+        ; restore old call frame
         mov     esp, ebp
-	pop     ebp
-	; return
-	ret
+        pop     ebp
+        ; return
+        ret
 ```
 
 The above assembly instructions cannot be achieved in our VM due to several

tutorial/en/4-Top-down-Parsing.md

@@ -120,13 +120,13 @@ calculator can be converted into:
 <expr_tail> ::= + <term> <expr_tail>
               | - <term> <expr_tail>
               | <empty>
-              
+
 <term> ::= <factor> <term_tail>
 
 <term_tail> ::= * <factor> <term_tail>
               | / <factor> <term_tail>
               | <empty>
-              
+
 <factor> ::= ( <expr> )
            | Num
 ```
@@ -211,13 +211,13 @@ void next() {
     while (*src == ' ' || *src == '\t') {
         src ++;
     }
-    
+
     token = *src++;
-    
+
     if (token >= '0' && token <= '9' ) {
         token_val = token - '0';
         token = Num;
-        
+
         while (*src >= '0' && *src <= '9') {
             token_val = token_val*10 + *src - '0';
             src ++;
@@ -231,7 +231,7 @@ void match(int tk) {
         printf("expected token: %d(%c), got: %d(%c)\n", tk, tk, token, token);
         exit(-1);
     }
-    
+
     next();
 }
 ```

tutorial/en/7-Statements.md

@@ -26,9 +26,9 @@ if (...) <statement> [else <statement>]
                                 JZ a
     <true_statement>   ===>     <true_statement>
   else:                         JMP b
-a:                           a:
-    <false_statement>           <false_statement>
-b:                           b:
+  a:                            a:
+      <false_statement>            <false_statement>
+  b:                            b:
 ```
 
 The flow of assembly code is: