anchor.diff:  let ch c =   skipChar c >>. ws
   let str s =  pstring s .>> ws
   
  +
  +// next two functions - part of lexer for c grammar
   let pLETTER: Parser<string, unit> = (many1Satisfy isLower .>> ws) <|> (many1Satisfy isUpper .>> ws) <|> str "_" <|> str "$" 
   
   
   let pNUMBER: Parser<float, unit> =  pfloat .>>  ws 
  +
   
   let pPLUS: Parser<string, unit> = str "+"
   
  
positive.code: 
  let literal s = pstring s .>> ws
  
  //keywords
  
  
  let (pVAR : Parser<string, unit>)  =
      let idStr = many1Satisfy isLower .>> ws // [a-z]+
  
negative.code:         else // reconstruct error
              Reply(reply.Status, reply.Error, reply.State)
  
  
  