Haskell: Format number with commas

Question

Is there a library function to put commas into numbers with Haskell? I can't find one for the life of me.

I want a function that would work something like this:

format 1000000 = "1,000,000"
format 1045.31 = "1,045.31"

but I can't seem to find any number formatting functions of this type in Haskell. Where are the number formatting functions?

Answer 1

Text.Printf

http://www.haskell.org/ghc/docs/6.12.1/html/libraries/base/Text-Printf.html

Answer 2

Perhaps you could use some of the functions from Data.Split:

http://hackage.haskell.org/cgi-bin/hackage-scripts/package/split

I know this isn't quite what you want, but you could use Data.List.intersperse

http://haskell.org/ghc/docs/6.12.1/html/libraries/base-4.2.0.0/Data-List.html#v:intersperse

EDIT: This does what you want, although I know you want a library function, this may be as close as you get (please excuse my poor coding style):

import Data.List.Split
import Data.List

format x = h++t
    where
        sp = break (== '.') $ show x
        h = reverse (intercalate "," $ splitEvery 3 $ reverse $ fst sp) 
        t = snd sp