On Thu, 14 Feb 2008, Cale Gibbard wrote:
I know Bulat will be terribly disappointed by my suggestion to make an addition to Data.List ;) but I mentioned the following couple of functions on #haskell and got some positive response that they were things other people ended up writing all the time as well, so I decided I'd propose them here as additions to Data.List and see what kind of reaction I got:
-- | The 'select' function takes a list and produces a list of pairs -- consisting of an element of the list together with a list of the -- remaining elements. select :: [a] -> [(a,[a])] select [] = [] select (x:xs) = (x,xs) : [(y,x:ys) | (y,ys) <- select xs]
-- | The 'selectSplit' function takes a list and produces a list of -- triples consisting of a prefix of the list, the element after it, -- and the remainder of the list. selectSplit :: [a] -> [([a],a,[a])] selectSplit [] = [] selectSplit (x:xs) = ([],x,xs) : [(x:lys,y,rys) | (lys,y,rys) <- selectSplit xs]
I use these functions regularly, too. select c = init $ zipWith (\xs (y:ys) -> (y, xs++ys)) (List.inits c) (List.tails c)