Conditions on deriving Typeable

[Simon Peyton-Jones]

It's a bug. Thank you


Simon

| -----Original Message-----
| From: glasgow-haskell-users-admin@haskell.org
[mailto:glasgow-haskell-users-admin@haskell.org]
| On Behalf Of George Russell
| Sent: 11 June 2003 13:07
| To: glasgow-haskell-users@haskell.org
| Subject: Conditions on deriving Typeable
|=20
| Please satisfy my curiosity, what is it about
|=20
|     data WrappedDisplayType =3D forall displayType .
|        DisplayType displayType =3D> WrappedDisplayType displayType
|           deriving (Typeable)
|=20
| that causes GHC 6.0 to utter
|=20
| DisplayTypes.hs:135:
|      Can't make a derived instance of `Typeable WrappedDisplayType'
|      (`WrappedDisplayType' has existentially-quantified
constructor(s))
|      When deriving instances for type `WrappedDisplayType'
|=20
| Obviously it doesn't like the existential quantifier, but why should
| that be a problem for Typeable?
|=20
| _______________________________________________
| Glasgow-haskell-users mailing list
| Glasgow-haskell-users@haskell.org
| http://www.haskell.org/mailman/listinfo/glasgow-haskell-users