anchor.diff:  	: variable(&var)	{ readelm(var); }
   	;
   
  -lsetstmt { int var,exp; }
  +lsetstmt { int var; int exp; }
   	:	LSETSYM variable(&var) '=' expression(&exp)
   				{ notyetimpl(); }
   	;
  
positive.code: 	  ]+
  	;
  
  pokestmt { int exp1,exp2 ; }
  	: POKESYM
  	  expression(&exp1)
  	  ','
  
negative.code: 	| /* empty */
  	;
  
  letstmt { int var; int exp; }
  	:	LETSYM		
  		variable(&var)		 { save_address(); }
  		'=' expression(&exp)  	 { assign(var,exp); }
  