Difference between revisions of "Data.List.Split"

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(make a list of ways to split)
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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.
 
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.
  +
  +
Some possible ways to split a list, to get your creative juices flowing:
  +
* what to split on?
  +
** single-element separator
  +
** sublist separator
  +
** use a list of possible separators instead of just one
  +
** use a predicate on elements or sublists instead of giving explicit separators
  +
** use approximate matching?
  +
* how to split?
  +
** discard the separators
  +
** keep the separators with the preceding or following splits
  +
** keep the separators as their own separate pieces of the result list
  +
** what to do with separators at the beginning/end? create a blank split before/after, or not?
   
 
Add your implementations below! Once we converge on something good we can upload it to hackage.
 
Add your implementations below! Once we converge on something good we can upload it to hackage.

Revision as of 16:39, 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.

Some possible ways to split a list, to get your creative juices flowing:

  • what to split on?
    • single-element separator
    • sublist separator
    • use a list of possible separators instead of just one
    • use a predicate on elements or sublists instead of giving explicit separators
    • use approximate matching?
  • how to split?
    • discard the separators
    • keep the separators with the preceding or following splits
    • keep the separators as their own separate pieces of the result list
    • what to do with separators at the beginning/end? create a blank split before/after, or not?

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"]