[Haskell-cafe] one-way monads

[Dan Piponi]

On Mon, May 19, 2008 at 10:54 PM, Zsolt SZALAI <zs.szalai at gmail.com> wrote:
> Now, i'm getting familiar with monads, but there is a little discredit
> about one-way monads.

If someone claims that monads are "one-way" they are probably
referring to the fact that it is impossible (without cheating!) to
write a function of signature Monad m => m a -> a. So I think there's
no 'discredit' here. For any specific monad, m, it's usually possible
to write a function m a -> a. But that's a distinct claim.
--
Dan