[Haskell-cafe] Why Kleisli composition is not in the Monad signature?

Brandon Allbery allbery.b at gmail.com
Tue Oct 16 19:46:25 CEST 2012

On Tue, Oct 16, 2012 at 1:19 PM, AUGER Cédric <sedrikov at gmail.com> wrote:

> What do you mean by demonstrate? If you do not want to fit the
> mathematical presentation, then I have nothing to demonstrate, you have
> your point of view, I have mine and they differ. Now, if you want to

I think the point is that Monad is not part of Haskell to satisfy
mathematical (or categorical) purity, but to solve a particular set of
problems.  Those problems are best addressed with bind, and join works
rather less well for them.  Since one of those problems involves
interfacing with the world outside of the program, an inefficient but
categorically/mathematically more "pure" solution may not be a viable
option in practice.

Alternative Preludes which focus on other purposes are a dime a dozen; if
you want a categorically pure Monad, nothing stops you from writing one and
using it.

brandon s allbery kf8nh                               sine nomine associates
allbery.b at gmail.com                                  ballbery at sinenomine.net
unix/linux, openafs, kerberos, infrastructure          http://sinenomine.net
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