anchor.diff:  }
   
   singlePv returns [FormulaAst result]
  -    :   pv EOF {result = $pv.result;}
  +    :   channel EOF {result = $channel.result;}
       ;
   
   formula returns [FormulaAst result]
  
positive.code:     :   '(' expression ')' {result = $expression.result;}
      ;
  
  pv returns [FormulaAst result]
      :   PV {result = channelFromToken($PV.text);}
      ;
  
  
negative.code: primary returns [FormulaAst result]
      :   functionExpression {result = $functionExpression.result;}
      |   parExpression {result = $parExpression.result;}
      |   channel {result = $channel.result;}
      |   numericLiteral {result = $numericLiteral.result;}
      |   stringLiteral {result = $stringLiteral.result;}
      |   constant {result = $constant.result;}
  