On Oct 20, 2010, at 5:06 PM, Thomas Schilling <nomin...@googlemail.com> wrote:
> Do we really want to treat every newtype wrappers as a form of 'id'? > For example: > > newtype Nat = Nat Integer -- must always be positive > > A possible rule (doesn't actually typecheck, but you get the idea): > > forall (x :: Nat). sqrt (x * x) = x > > If we ignore newtyping we get an incorrect rewrite rule. It depends > on the exact implementation of which 'id's would be recognised. > That wouldn't be generalized to id, the special treatment would only apply to rule that _mention_ Prelude.id explicitly. Such rules would implicitly fire when, say, "fmap Nat xs" occurs because Nat would be considered a specialization of id in the (pattern side of) rule "fmap id = id". Rules mentioning Nat would not be magical in any way. -- James_______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
