Ivan Miljenovic wrote:
> 2010/1/27 Tony Morris <[email protected]>:
>
>> It might be more obvious by giving:
>>
>> fromMaybe :: a -> (a -> x, x) -> x
>>
>
> I actually found this more confusing, and am not sure of its validity:
> should that be "Maybe a" there at the beginning?
>
>
Sorry a mistake. Correction: fromMaybe :: a -> ((a -> x, x) -> x) -> x
{-# LANGUAGE RankNTypes #-}
data Maybe' a = M (forall x. (a -> x, x) -> x)
to :: Maybe' t -> Maybe t
to (M f) = f (Just, Nothing)
from :: Maybe a -> Maybe' a
from (Just a) = M (flip fst a)
from Nothing = M snd
--
Tony Morris
http://tmorris.net/
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