[Haskell-cafe] Monads and Functions sequence and sequence_

[Gregory Crosswhite]

The expression

     sequence [a,b,c,...]

is roughly equivalent to

     do
         r_a <- a
         r_b <- b
         r_c <- c
         ...
         return [r_a,r_b,r_c,...]

The expression

     sequence_ [a,b,c,...]

is roughly equivalent to

     do
         a
         b
         c
         ...
         return ()

Does that help?

Cheers,
Greg

On 10/29/10 10:07 PM, 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.
>
> Even references to some research papers that explain the rationale behind these (and all the other..?) monad functions would be great.
>
> Thanks in advance,
>
>
> Mark Spezzano
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