anchor.diff:  	|	(WHILE expr DO stat_seq ENDDO SEMI) -> ^(WHILE expr stat_seq)
   	|	(FOR ID ASSIGN range DO stat_seq ENDDO SEMI) -> ^(FOR range stat_seq)
   	|	BREAK SEMI -> BREAK
  -	|	RETURN expr SEMI
  +	|	RETURN expr SEMI -> ^(RETURN expr)
   	|	block
   	|	funct_call SEMI -> funct_call
   	;
  
positive.code: 	;
  
  funct_declaration
  	:	ret_type FUNCTION ID LPAREN param_list RPAREN BEGIN block_list END SEMI
  	;
  	
  main_function
  
negative.code: 	;
  	
  param_list_tail
  	:	COMMA param param_list_tail -> ^(COMMA param param_list_tail)
  	|	
  	;
  	
  