[Haskell-cafe] one-way monads

Dan Piponi dpiponi at gmail.com
Tue May 20 13:47:30 EDT 2008

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.

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