The problem is, that the type parameter 'a' of the functions in the list is
fixed. You can work around that with RankNTypes:
newtype Wrap = Wrap { unwrap :: forall a. [a] -> a }
unwrap $ (\(h:t) -> (unwrap h) t) [Wrap head, Wrap last]
This specializes the type of the functions at every point of use separately.
On 7 March 2014 09:14, Kolář Dušan
Well my fault, the example should have been like this:
We have and error of infinite type for Prelude> :t ((\(h:t) -> h t) [head, last, head, last, head, last])
Of course, head and tail are incompatible on type level...
Dušan
On Fri, 07 Mar 2014 07:57:09 +0100, Kolář Dušan
wrote:
: :
But we have an error of infinite type construction for
Prelude> :t ((\(h:t) -> h t) [head,tail, head, tail, head, tail])
Well I can overcome this by encoding functions into data types and then performing "conversion" back and forth, nevertheless, is there any way how to overcome this?
It seems like you need heterogenous collections[0]
Regards, Henk-Jan van Tuyl
[0] http://www.haskell.org/haskellwiki/Heterogenous_collections
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