anchor.diff:  // Integer literals
   IntegerLiteral
   	:	'0'
  -	|	Sign? NonZeroDigit Digits*
  +	|	NonZeroDigit Digits*
   	;
   
   FloatingPointLiteral
  -	:	Sign? Digits '.' Digits?
  +	:	Digits '.' Digits
   	;
   
   fragment
  
positive.code: 	|	literal						# LiteralExpression
  	|	Identifier			        # IdentifierExpression
  	|	expression Operator=(INC|DEC)		# PostIncDecExpression
  	|	SUB expression				# UnaryMinusExpression
  	|	BANG expression				# NotExpression
  	|	expression
  		Operator=(		
  			MUL 
  		|	DIV
  		|	MOD
  
negative.code: 	:	[1-9]
  	;
  	
  // Separators
  LPAREN	: '(';
  RPAREN	: ')';
  