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