[Haskell-cafe] one-way monads

[ajb at spamcop.net]

G'day all.

Quoting Dan Piponi <dpiponi at gmail.com>:

> For any specific monad, m, it's usually possible
> to write a function m a -> a.

Actually, it's true less than 50% of the time.  In particular, it's
not true of any monad transformer.

Cheers,
Andrew Bromage