CODEWITHSUNDEEP
haskellsplit
Haskfan
Haskfan

Reputation: 35

How can I split a list in Haskell through an added element of a list?

I have a given char or num, and I want to split a list at the same characters or numbers. split a "heyahelloaeveryone" == "hey,hello,everyone " the type should be : Eq a => a -> [a]

split _ [] = []
split c (x:xs)
  | c == x = [[]] ++ split c xs
  | otherwise = (x : head(split c xs)) : tail(split c xs)

I've tried with this, but this code doesn't work for these situations: split a [a] == [[],[]] split a [] == []

Upvotes: 1

Views: 116

Answers (2)

jf_
jf_

Reputation: 3479

You can initialize your list with the first element as an empty list. This way you start correctly with the type (list of lists) you want to have.

However, the resulting type is split :: Eq a => a -> [a] -> [[a]]

split _ [] = [[]]
split c (x:xs)
  | c == x = [[]] ++ split c xs
  | otherwise = (x : head(split c xs)) : tail(split c xs)

Upvotes: 1

willeM_ Van Onsem
willeM_ Van Onsem

Reputation: 476557

For an empty list, you will need to return a singleton list as well. This of course then conflicts with split a [] == [], but we can first perform a check, and only if the given list is not empty, perform a recursive algorithm:

split :: Eq a => a -> [a] -> [[a]]
split _ [] = []  -- ← empty list for an empty list
split c ls = go ls
    where go [] = [[]]  -- ← single empty list for an empty list
          go (x:xs) | c == x = [] : go xs
                    | otherwise = (x:y) : ys
              where ~(y: ys) = go xs

This gives us the expected value for split 'a' "a":

Prelude> split 'a' ""
[]
Prelude> split 'a' "a"
["",""]
Prelude> split 'a' "foobar"
["foob","r"]
Prelude> split 'a' "foobarqux"
["foob","rqux"]
Prelude> split 'a' "foobaarqux"
["foob","","rqux"]

Upvotes: 0

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