Glurk wrote:
Is it possible to use function composition with a function that takes more than 1 parameter ?
For example, I have a function that finds all the matches of an element within a list :-
matches x xs = [ m | m <- xs, x == m ]
So, matches 'e' "qwertyee" will return "eee"
I now want a function that will work out how many times the element occurs in the list, easily written as :-
howMany x xs = length $ matches x xs
The lambdabot on #haskell has a plugin named "pointless" that can transform this into a definition that doesn't mention x and xs anymore. I think it will propose howMany = (length .) . matches And with matches x xs = filter (x==) xs matches x = filter (x==) matches = filter . (==) we have howMany = (length .) . filter . (==)
I've tried various things, like putting brackets around (length . matches) and changing my function to take in a tuple of (element, list), instead of 2 parameters (which I thought I had working at some stage ! but which now I can't get to work)
howMany = curry (length . uncurry matches) Regards, apfelmus