Haskell: Could not find module `Data.List.Split'

Question

I'm trying to split a list in Haskell. As to my knowledge, the easiest way to do this is with splitOn, but this function requires Data.List.Split, so I tried to run import Data.List.Split in Prelude. However, I got the following error:

Could not find module Data.List.Split

Simply importing Data.List does work, however.

What could I do to solve this? Or, even better: is there an easy, built-in alternative to split lists?

What do you want to split the list on? Is it, by any chance, a String you want to split on '\n' or \s+? — Zeta
– Zeta, Commented Dec 9, 2015 at 9:45
I'm sorry, I should have been clearer. I would like to split a String on whitespaces. — TheLeonKing
– TheLeonKing, Commented Dec 9, 2015 at 10:11
You do know about cabal or stack, right? — BTW, it's also quite easy to split lists with tools from base only... — leftaroundabout
– leftaroundabout, Commented Dec 9, 2015 at 10:52
@Algorithm_NL: Then this is a XY problem. You were actually trying to split a string, but asked about your (non-working) solution. — Zeta
– Zeta, Commented Dec 9, 2015 at 12:08
@Zeta Wow, I didn't realize that. Thanks for the clarification! — TheLeonKing
– TheLeonKing, Commented Dec 9, 2015 at 13:23

epsilonhalbe · Accepted Answer · 2015-12-09 13:17:47Z

14

Data.List.Split is not in the base I think you'll have to install split

Update

after the clarification in the comments that only splitting on whitespace is required - use words/lines to your need - see also @Zeta's answer.

edited Dec 9, 2015 at 13:17

answered Dec 9, 2015 at 9:34

epsilonhalbe

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6 Comments

TheLeonKing Over a year ago

Good to know, thanks. Would there be any way to do this without installing packages?

epsilonhalbe Over a year ago

but I think it is in the haskell plattform - since ghc-7.8, and even though it is not "safe" for small projects using ghc-7.6 I just copy paste the code in some module to not depend on the whole split package

epsilonhalbe Over a year ago

if you add a split == 0.2.2 to your build-depends:-statements it is quite simple to install the package - why would you like to avoid it?

Zeta Over a year ago

@epsilonhalbe: Maybe he doesn't even use a .cabal or .yaml file and only wants to write a stand-alone Haskell script for runhaskell.

epsilonhalbe Over a year ago

sometimes I don't think about the obvious use-cases

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Zeta · Accepted Answer · 2015-12-09 12:06:51Z

8

To split a String on arbitrary white space (e.g. any Char c where Data.Char.isSpace c is True), use words:

-- words :: String -> [String]
ghci> words "Hello World, I'm a string \n example   \r\t with white space"
["Hello","World,","I'm","a","string","example","with","white","space"]

No need for additional imports, since words is part of the Prelude.

answered Dec 9, 2015 at 12:06

Zeta

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2 Comments

mherzl Over a year ago

How do you split on a given string that is not necessarily whitespace? For example when reading a csv file.

Zeta Over a year ago

@user3224967 CSV is a lot more complicate than that, since " breaks delimiter, e.g. Mayer;John;"Department of StackOverflow; Washington" is a record with three, not four fields.

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