-----BEGIN PGP SIGNED MESSAGE----- Hash: SHA512 I've read this blogpost about the "trivial monad" http://sigfpe.blogspot.com/2007/04/trivial-monad.html, because I still don't understand what this monad thingy is all about.
The author defines three functions: data W a = W a deriving Show return :: a -> W a return x = W x fmap :: (a -> b) -> (W a -> W b) fmap f (W x) = W (f x) bind :: (a -> W b) -> (W a -> W b) bind f (W x) = f x and asks the reader to prove the tree monad laws for them. However I don't understand the type signatures for bind and fmap. I'd say (and ghci's type inference agrees) that bind and fmap have the type bind:: (a->W b) -> W a -> W b fmap:: (a->b) -> W a -> W b They take a function f and something and return what f does to that. I don't see why they should return a function. This of course makes it hard for me to prove the monad laws. The first however works nonetheless: 1) bind f (return a)= f a => bind f (return a)= bind f (W a) = f a Can someone explain bind and fmap (and possible law 2 and 3)? Thanks, Adrian -----BEGIN PGP SIGNATURE----- Version: GnuPG v1.4.6 (Darwin) Comment: Using GnuPG with Mozilla - http://enigmail.mozdev.org iD8DBQFGOuQS11V8mqIQMRsRCmngAJ9NwQMwXeS/PSM1NUsVA8gxPuA0KACfSLiA ItqRZW5a4XyQ099bhMtSWmU= =/8i/ -----END PGP SIGNATURE----- _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
