Re: [Haskell-cafe] Monadic correctness

On Sat, Oct 17, 2009 at 3:21 PM, Andrew Coppin <andrewcoppin@btinternet.com> wrote:

Suppose we have

 newtype Foo x  instance Monad Foo  runFoo :: Foo x -> IO x

What sort of things can I do to check that I actually implemented this correctly? I mean, ignoring what makes Foo special for a moment, how can I check that it works correctly as a monad.

Anything which satisfies the monad laws is a monad. In other words, do you have: return a >>= f = f a m >>= return = m (m >>= f) >>= g = m >>= (\a -> f a >>= g) When I bother, I usually just work out the proofs by hand. -- Dave Menendez <dave@zednenem.com> <http://www.eyrie.org/~zednenem/>