[Haskell-beginners] Why is this not a "category"?

Arjun Comar nrujac at gmail.com
Sat Mar 29 05:47:01 UTC 2014


You're misreading the question. It's asking you to show that the category
induced by the <= relation fails associativity if you add an extra
morphism.
On Mar 29, 2014 1:19 AM, "John M. Dlugosz" <ngnr63q02 at sneakemail.com> wrote:

> on https://en.wikibooks.org/w/index.php?title=Haskell/
> Category_theory&stable=0#Hask.2C_the_Haskell_category
>
> the second exercise in the box (see illustration there) asks
> "(Harder.) If we add another morphism to the above example, it fails to be
> a category. Why? Hint: think about associativity of the composition
> operation."
>
> There are no answers-to-exercises.  Can someone explain to me why adding
> another function with the same type causes the Haskell type system to no
> longer form the Hask category?
>
> (scratching head)
>
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