Re: [Haskell-cafe] Why Kleisli composition is not in the Monad signature?

Ertugrul Söylemez wrote:

damodar kulkarni wrote:

...

The Monad class makes us define bind (>>=) and unit (return) for our monads.

Why the Kleisli composition (>=>) or (<=<) is not made a part of Monad class instead of bind (>>=)?

Is there any historical reason behind this?

The bind (>>=) is not as elegant as (>=>), at least as I find it.

Am I missing something?

Try to express

do x <- getLine y <- getLine print (x, y)

using only Kleisli composition (without cheating). Through cheating (doing non-categorical stuff) it's possible to implement (>>=) in terms of (<=<), but as said that's basically breaking the abstraction.

What do you mean with "cheating" / "doing non-categorical stuff"? m >>= f = (const m >=> f) () f >=> g = \x -> f x >>= g How does the first definition "break the abstraction" while the second does not? Cheers -- Ben Franksen () ascii ribbon campaign - against html e-mail /\ www.asciiribbon.org - against proprietary attachments