Question

I am developing Pascal language parser in Haskell using Parsec library and I need to re-define some tokens defined in Parsec.Token class.

Speeking of it, here is my case:

I need to change how stringLiteral token is matched. In default definition, it is something between char '"' (see this), but I need it to be between '\'' (apostrophes). How can I do this modification to Parsec behavior?

Thanks!!!

Answer 1

You are talking about adjusting the field of a data type named GenTokenParser. It looks like you are using a function that automatically fills in the data type with sensible defaults and you just want to adjust one thing, here you go:

 myMakeTokenParser langDef =
    let default = makeTokenParser langDef
    in default { stringLiteral = newStringLit }
  where
  newStringLit = lexeme (
                      do{ str <- between (char '\'')
                                         (char '\'' <?> "end of string")
                                         (many stringChar)
                        ; return (foldr (maybe id (:)) "" str)
                        }
                      <?> "literal string")