On Tuesday 14 March 2006 14:46, Pete Chown wrote:
Shannon -jj Behrens wrote:
Arrows looks like a replacement for monads. Are you saying I should drop my use of the State monad? If so, why? I like the readability of the do syntax.
Okay, now it's my turn to ask a question. :-) I've read about arrows, and while I think I see what they do, I'm not sure why they are seen as so special that they even get new syntax. This question of Shannon's is exactly the point I struggle with. I can see that the arrow operators might be useful with functions, but are they useful for other things too?
Yes, http://www.haskell.org/arrows/biblio.html lists a number of papers describing non-trivial applications of Arrows, that is, Arrows other than (->). I found the exposition in http://www.haskell.org/yale/papers/oxford02/ to be quite readable.
For example, as monads are one kind of arrow, I thought I would make some of the I/O functions into arrows and see what happened. The result was pretty much the same as using the monad, except slightly less convenient.
You can write monadic code without ever using the syntax sugar, and get along. However, do-notation is convenient. OTOH, I am told that programming with Arrows is really quite inconvenient w/o the syntax sugar. Cheers, Ben