[Haskell-cafe] how do I avoid excessive constructor application?
S. Alexander Jacobson
alex at alexjacobson.com
Wed Mar 2 09:20:15 EST 2005
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?
S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com
On Wed, 2 Mar 2005, Henning Thielemann wrote:
> On Wed, 2 Mar 2005, Ben Lippmeier wrote:
>> You can play games with the type checker to force them to have the same
>> type without changing the "meaning" of your function.
>> fun1' f (Left x) = if True then Left (f x) else Left x
> Left (f x) `asTypeOf` Left x
More information about the Haskell-Cafe