[Haskell-cafe] Article review: Category Theory

Ulf Norell ulfn at cs.chalmers.se
Fri Jan 19 05:23:31 EST 2007


On Jan 18, 2007, at 10:09 PM, Yitzchak Gale wrote:

> I wrote:
>>> Will (id :: A -> A $!) do the trick?
>
> Ulf Norell wrote:
>> The problem is not with id, it's with composition. For any f and g we
>> have
>>
>> f . g = \x -> f (g x)
>>
>> So _|_ . g = \x -> _|_ for any g.
>
> OK, so then how about
>
> f .! g = ((.) $! f) $! g

That should probably do the trick.

/ Ulf


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