# Difference between revisions of "Data.List.Split"

From HaskellWiki

Line 26: | Line 26: | ||

return (c:head, tail) | return (c:head, tail) | ||

chopWith delimiter [] = Nothing | chopWith delimiter [] = Nothing | ||

+ | -- note: chopWith could be make 'more efficient' i.e. remove the >>=\-> bit | ||

+ | -- by adding an accumulator | ||

+ | |||

unintercalate delimiter = unfoldr (chopWith delimiter) | unintercalate delimiter = unfoldr (chopWith delimiter) |

## Revision as of 16:34, 13 December 2008

A theoretical module which contains implementations/combinators for implementing every possible method of list-splitting known to man. This way no one has to argue about what the correct interface for split is, we can just have them all.

Add your implementations below! Once we converge on something good we can upload it to hackage.

```
{-# LANGUAGE ViewPatterns #-}
import Data.List (unfoldr)
-- intercalate :: [a] -> [[a]] -> [a]
-- intercalate x [a,b,c,x,y,z] = [a,x,b,x,c,x,x,y,x,z,x]
-- unintercalate :: [a] -> [a] -> [[a]]
-- unintercalate x [a,x,b,x,c,x,x,y,x,z,x] = [a,b,c,[],y,z]
-- unintercalate is the "inverse" of intercalate
match [] string = Just string
match (_:_) [] = Nothing
match (p:ps) (q:qs) | p == q = match ps qs
match (_:_) (_:_) | otherwise = Nothing
chopWith delimiter (match delimiter -> Just tail) = return ([], tail)
chopWith delimiter (c:cs) = chopWith delimiter cs >>= \(head, tail) ->
return (c:head, tail)
chopWith delimiter [] = Nothing
-- note: chopWith could be make 'more efficient' i.e. remove the >>=\-> bit
-- by adding an accumulator
unintercalate delimiter = unfoldr (chopWith delimiter)
-- > unintercalate "x" "axbxcxxyxzx"
-- ["a","b","c","","y","z"]
```