How to split a string in Haskell?
In the module Text.Regex (part of the Haskell Platform), there is a function:
splitRegex :: Regex -> String -> [String]
which splits a string based on a regular expression. The API can be found at Hackage.
Remember that you can look up the definition of Prelude functions!
http://www.haskell.org/onlinereport/standard-prelude.html
Looking there, the definition of words
is,
words :: String -> [String]
words s = case dropWhile Char.isSpace s of
"" -> []
s' -> w : words s''
where (w, s'') = break Char.isSpace s'
So, change it for a function that takes a predicate:
wordsWhen :: (Char -> Bool) -> String -> [String]
wordsWhen p s = case dropWhile p s of
"" -> []
s' -> w : wordsWhen p s''
where (w, s'') = break p s'
Then call it with whatever predicate you want!
main = print $ wordsWhen (==',') "break,this,string,at,commas"
If you use Data.Text, there is splitOn:
http://hackage.haskell.org/packages/archive/text/0.11.2.0/doc/html/Data-Text.html#v:splitOn
This is built in the Haskell Platform.
So for instance:
import qualified Data.Text as T
main = print $ T.splitOn (T.pack " ") (T.pack "this is a test")
or:
{-# LANGUAGE OverloadedStrings #-}
import qualified Data.Text as T
main = print $ T.splitOn " " "this is a test"
There is a package for this called split.
cabal install split
Use it like this:
ghci> import Data.List.Split
ghci> splitOn "," "my,comma,separated,list"
["my","comma","separated","list"]
It comes with a lot of other functions for splitting on matching delimiters or having several delimiters.