[Haskell-cafe] Design Patterns by Gamma or equivalent
g9ks157k at acme.softbase.org
Tue Mar 17 05:34:11 EDT 2009
Am Dienstag, 17. März 2009 05:09 schrieb wren ng thornton:
> ajb at spamcop.net wrote:
> > Or to put it another way, category theory is the pattern language of
> > mathematics.
> Indeed. Though, IMO, there's a distinction between fairly banal things
> (e.g. monoids),
Monoids aren’t a concept of category theory. There are a generalization of
groups. So they more belong to group theory.
By the way, the documentation of Control.Category says that a category is a
monoid (as far as I remember). This is wrong. Category laws correspond to
monoid laws but monoid composition is total while category composition has
the restriction that the domain of the first argument must match the codomain
of the second.
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