Julien Oster wrote: > While we're at it: The best thing I could come up for > > func2 f g l = filter f (map g l) > > is > > func2p f g = (filter f) . (map g) > > Which isn't exactly point-_free_. Is it possible to reduce that further?
Sure it is: func2 f g l = filter f (map g l) func2 f g = (filter f) . (map g) -- definition of (.) func2 f g = ((.) (filter f)) (map g) -- desugaring func2 f = ((.) (filter f)) . map -- definition of (.) func2 f = flip (.) map ((.) (filter f)) -- desugaring, def. of flip func2 = flip (.) map . (.) . filter -- def. of (.), twice func2 = (. map) . (.) . filter -- add back some sugar The general process is called "lambda elimination" and can be done mechanically. Ask Goole for "Unlambda", the not-quite-serious programming language; since it's missing the lambda, its manual explains lambda elimination in some detail. I think, all that's needed is flip, (.) and liftM2. Udo. -- I'm not prejudiced, I hate everyone equally.
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