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