[Haskell-cafe] Re: Re: Re: monad subexpressions

david48 wrote:

On 8/3/07, Neil Mitchell wrote:

...

Hmm, interesting. Consider:

let x = 12 let x = (<- x)

Wouldn't that be forbidden ?

I'd expect the x in ( <- x ) have to be of type m a.

Yes, unless of course you did: instance (Monad m, Num n) => Num (m n) or some such nonsense. :)

If you meant :

x <- return 12 let x = ( <- x )

This would be equally wrong. Perhaps you meant: do let x = return 12 let x = (<- x) ... Then this would become: do let x = return 12 t1 <- x let x = t1 ... Which is, in turn: let x = return 12 in x >>= (\t1 -> let x = t1 in ...) -- Chris Smith