On 7 October 2010 12:04, Sebastiaan Visser <[email protected]> wrote:
> What exactly are the benefits of Monad comprehensions over, for example, the
> do-notation or idioms?
List comprehensions are just a specialisation of the do-notation for lists.
Monad comprehensions are a generalisation for arbitrary monads of this
specialisation :-)
I don't think there are major benefits to this. The major change is
that they "look like" lists (which might be important if you are
writing a SQL library) and the final "return" is hoisted into the head
of the comprehension [HERE | with, the, usual, do, notation, sequence,
here].
> I'm not fully aware of what Monad comprehensions would offer in general, but
> aren't most comprehensions directly translatable to applicative style?
Monadic style, not applicative style.
> For example:
>
> [(x, y) | x <- xs | y <- ys] -- Comprehension.
This computes a zip of xs and ys.
> (,) <$> xs <*> ys -- Applicative style.
This actually computes a cartesian product instead.
You are right in spirit because:
[e | qs] ==> do { qs; return e }
For example:
[(x, y) | x <- xs, y <- ys] ==> do { x <- xs; y <- ys; return (x, y) }
Cheers,
Max
_______________________________________________
Glasgow-haskell-users mailing list
[email protected]
http://www.haskell.org/mailman/listinfo/glasgow-haskell-users
