[Haskell-cafe] Re: Monads and Functions sequence and sequence_

[Bardur Arantsson]

On 2010-10-30 07:07, Mark Spezzano wrote:
> Hi,
>
> Can somebody please explain exactly how the monad functions "sequence" and "sequence_" are meant to work?
>
> I have almost every Haskell textbook, but there's surprisingly little information in them about the two functions.
>
>  From what I can gather, "sequence" and "sequence_" behave differently depending on the types of the Monads that they are processing. Is this correct? Some concrete examples would be really helpful.
>

sequence [m1,m2,m3,m4,...] = do
   x1 <- m1
   x2 <- m2
   x3 <- m3
   x4 <- m4
   ...
   return [x1,x2,x3,x4,...]

sequence_ [m1,m2,m3,m4,...] = do
   m1
   m2
   m3
   m4
   ...
   return ()

Cheers,