Hans van Thiel wrote:
On Wed, 2009-06-17 at 21:26 -0500, Jake McArthur wrote:
Jon Strait wrote:
I'm reading the third (bind associativity) law for monads in this form:
m >>= (\x -> k x >>= h) = (m >>= k) >>= h
Arguably, that law would be better stated as:
(h <=< k) <=< m = h <=< (k <=< m)
This wouldn't be so unintuitive.
Hi,
The only place I've ever seen Kleisli composition, or its flip, used is
in demonstrating the monad laws. Yet it is so elegant and, even having
its own name, it must have some practical use. Do you, or anybody else,
have some pointers?
import Prelude hiding (mapM)
import Data.Traversable (mapM)
import Control.Monad ((<=<))
newtype Fix f = Fix { unFix :: f (Fix f) }
cata phi = phi . fmap (cata phi) . unFix
cataM phiM = phiM <=< (mapM (cataM phiM) . unFix)
ana psi = Fix . fmap (ana psi) . psi
anaM psiM = (liftM Fix . mapM (anaM psiM)) <=< psiM
etc. It's great for anyone who enjoys point-free style but wants to work
with monads.
--
Live well,
~wren
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