yes. a newtype declares a new type isomorphic to an existing type.
newtype T = MkT S
declares T to be isomorphic to S.
There is no existing Haskell type isomorphic to your Dynamic.
In concrete terms, the newtype constructor is discarded before we get to
System F; but we can't do that with an existential.
S
| -----Original Message-----
| From: [EMAIL PROTECTED]
[mailto:glasgow-haskell-bugs-
| [EMAIL PROTECTED] On Behalf Of Ralf Hinze
| Sent: 18 November 2005 13:28
| To: [email protected]
| Subject: newtype and existentials
|
| Is there a strong reason why
|
| > {-# OPTIONS -fglasgow-exts #-}
| > data Type :: (* -> *) where
| > Int :: Type Int
| > data Dynamic = forall a . Dyn (a, Type a)
|
| works, but not
|
| > newtype Dynamic = forall a . Dyn (a, Type a)
|
| Cheers, Ralf
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