Re: [Haskell-cafe] Name that function =)

Hi Louis, Try foo = liftM2, and check out the recent haskell thread "Cannot understand liftM2". Cheers, - Conal On 12/12/06, Louis J Scoras wrote:

Hi all;

I'm new to the list, so I just wanted to say hi and -- of course -- ask a quick question:

I have some IO actions that I want to map over a list of pairs -- these are just directory names and their down-cased versions. It wasn't difficult to actually get the right behavior by just doing mapM twice.

-- putDirs just outputs something like "mv fst snd" mapM_ putDirs pairs mapM_ (uncurry renameFile) pairs

This bothered me though, because I suspected that this could be done in one pass. Naively I proceeded to this.

mapM_ (putDirs >> (uncurry renameFile)) pairs

Which didn't work. I thought about it a little more before realizing that putDirs wouldn't get any parameters this way: I needed some way to distribute the pair over both operations. Here's the higher-order function I needed:

foo h f g i = h (f i) (g i)

which could then be curried and we get:

mapM_ (foo (>>) putDirs $ uncurry renameFile) pairs

Works great. So my question: is there a established name for foo? What about foo partially applied to (>>)? This was a fun exercise, but I'd like to use the standard implementations if they exist.

Thanks!

-- Lou. _______________________________________________ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe