anchor.diff:  
   addop: '-' | '+';
   
  -term: term multop factor | factor;
  +term: factor (multop factor)*;
   
   multop: '*' | '/' | '%';
   
   factor: '(' simple_expression ')' | constant;
   
   constant:
  -	INTEGER
  +	integer
   	| TRUE
   	| FALSE
   	| 'next'
  
positive.code: or_expression:
  	unary_relationexpression ('&&' unary_relationexpression)*;
  
  unary_relationexpression: ('!' unary_relationexpression)
  	| relation_expression;
  
  relation_expression: (add_expression relop add_expression)
  	| add_expression;
  
  relop: '<=' | '>=' | '==' | '!=' | '>' | '>';
  
  
negative.code: 
  while_statement: WHILE '(' expression ')' statement;
  
  expression: (variable (exprop expression)*) | simple_expression;
  
  exprop: '=' | '-+' | '*=' | '/=' | '+=';
  
  