Re: [Haskell-cafe] how do I avoid excessive constructor application?

2 Mar 2005


      On Wed, 2 Mar 2005 09:20:15 -0500 (Eastern Standard Time), S.
Alexander Jacobson  wrote:
...
My point was that this code seems excessively complex:
fun::(a->a1)->(Either a b)->Either a1 b
   fun f (Left x) = Left (f x)
   fun _ r@(Right x)= Right x
I'd like to avoid the destruction and construction in the third line
by replacing the right hand side with r.  However, the typechecker
then claims my type is wrong.  How do I fix that?
In your example, 'r' has type "Either a b" which doesn't match "Either
a1 b". And you can "fix" it with some unsafeCoerce# magic. (:

-- 
Friendly,
  Lemmih