haskell:
Hello,
I was just doing Exercise 7.1 of Hal Daum?'s very good "Yet Another Haskell Tutorial". It consists of 5 short functions which are to be converted into point-free style (if possible).
It's insightful and after some thinking I've been able to come up with solutions that make me understand things better.
But I'm having problems with one of the functions:
func3 f l = l ++ map f l
Looks pretty clear and simple. However, I can't come up with a solution. Is it even possible to remove one of the variables, f or l? If so, how?
The solution is to install lambdabot ;) Point free refactoring: lambdabot> pl func3 f l = l ++ map f l func3 = ap (++) . map Find the type: lambdabot> type ap (++) . map forall b. (b -> b) -> [b] -> [b] Get some free theorems: lambdabot> free f :: (b -> b) -> [b] -> [b] f . g = h . f => map f . f g = f h . map f :) -- Don