Split a string by a chosen character in haskell

Question

I\'m trying to split a string every time there is a chosen character. So if I receive \"1,2,3,4,5\", and my chosen character is \",\" the result is a l

Answer 1

Basically this is a foldring job. So you may simply do like

λ> foldr (\c (s:ss) -> if c == ',' then "":s:ss else (c:s):ss) [""] "1,2,3,42,5"
["1","2","3","42","5"]

So;

splitOn x = foldr (\c (s:ss) -> if c == x then "":s:ss else (c:s):ss) [""]

However this will give us reasonable but perhaps not wanted results such as;

λ> splitOn ',' ",1,2,3,42,5,"
["","1","2","3","42","5",""]

In this particular case it might be nice to trim the unwanted characters off of the string in advance. In Haskell though, this functionality i guess conventionally gets the name

dropAround :: (Char -> Bool) -> String -> String
dropAround b = dropWhile b . dropWhileEnd b

λ> dropAround (==',') ",1,2,3,42,5,"
"1,2,3,42,5"

accordingly;

λ> splitOn (',') . dropAround (==',') $ ",1,2,3,42,5,"
["1","2","3","42","5"]

Answer 2

If you're using GHC it comes with the standard Prelude and the modules in the base package, and perhaps a few other packages.

Most packages, like the split package (which contains the Data.List.Split module), aren't part of GHC itself. You'll have to import them as an explicit compilation step. This is easiest done with a build tool. Most Haskellers use either Cabal or Stack.

With Stack, for example, you can add the split package to your package.yaml file:

dependencies:
- base >= 4.7 && < 5
- split

You can also load an extra package when you use Stack to start GHCi. This is useful for ad-hoc experiments.

Answer 3

‘Data.List.Split’ is not in prelude and needs to be installed as a dependency package. Install command depends on environment you are using: ‘stack install split’ for stack ‘cabal install split’ for cabal