Re: [Haskell-beginners] functional parser type error

There is working code to accompany the book on Graham Hutton's website that wraps Parser as a newtype. http://www.cs.nott.ac.uk/~gmh/book.html http://www.cs.nott.ac.uk/~gmh/Parsing.lhs Graham makes a brief comment about the difference at the end of the parsing chapter. On 4 April 2012 18:31, Brent Yorgey wrote:

In order to use do-notation, Parser has to be an instance of Monad. However, ((->) String) is already an instance of Monad, and it's not the instance you want for Parser.  There cannot be two instances for the same type, so you must wrap it in a newtype in order to make a different instance.