On Thu, 17 Jan 2008, Henning Thielemann wrote:
On Thu, 17 Jan 2008, Twan van Laarhoven wrote:
Hello Haskellers,
An often requested function is 'split', to split a list into parts delimited by some separator. ByteString has the functions split and splitWith for this purpose. I propose we add equivalents to Data.List:
split :: Eq a => a -> [a] -> [[a]] split x = splitWith (x==)
splitWith :: (a -> Bool) -> [a] -> [[a]] splitWith p xs = ys : case zs of [] -> [] _:ws -> splitWith p ws where (ys,zs) = break p xs
trac: http://hackage.haskell.org/trac/ghc/ticket/2048 deadline: two weeks from now, January 30
The type could be more specific. We know that the result list is always non-empty, and that the first element of each sub-list matches 'p', except the leading sub-list. Ideally we had a list type for elements of alternating type, like this one: http://darcs.haskell.org/event-list/src/Data/AlternatingList/List/Uniform.hs Then we could use the signature: splitWith :: (a -> Bool) -> [a] -> AlternatingList.T [a] a
We can simulate this type by: splitWith :: (a -> Bool) -> [a] -> ([a], [(a, [a])])
Ah, I see that your function filters out the elements, that match 'p'. This simplifies the resulting list type ...