18 Jan
2007
18 Jan
'07
9:05 a.m.
On Jan 16, 2007, at 7:22 PM, David House wrote:
Hey all,
I've written a chapter for the Wikibook that attempts to teach some basic Category Theory in a Haskell hacker-friendly fashion.
In the section on the category laws you say that the identity morphism should satisfy f . idA = idB . f This is not strong enough. You need f . idA = f = idB . f Unfortunately, fixing this means that the category Hask is no longer a category since _|_ . id = \x -> _|_ ≠ _|_ Also it's a bit strange to state that morphisms are closed under composition after the associativity law. Wouldn't it be nicer to introduce composition as a total operation off the bat? / Ulf