[Haskell-cafe] Explaining monads

Brian Brunswick brian at ithil.org
Tue Aug 14 13:53:01 EDT 2007

On 14/08/07, Jeff Polakow <jeff.polakow at db.com> wrote:
> Of course, the type [Int] denotes a value which is a list of Ints;
> additionally [Int] can be viewed as a value representing the
> nondeterministic computation of a single Int. Generally, the type Monad m =>
> m Int can be viewed as a value representing the computation of an Int.

But thats not really right. What exactly m Int does /depends/ on m. It might
represent 0 or more computations
of Int, or computations of Int carrying some extra stuff around, or complex
control logic about what the computation does

All that is really given, is that we can feed another 'Int->m a' thingy to
it using bind, and get back an m a, and the
thingy we fed in might even be used zero or more times while doing it.

These 'thingy's are called Kleisli Arrows, by the way.

Brian_Brunswick____brian at ithil.org____Wit____Disclaimer____!Shortsig_rules!
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