A formatting function to go from numbers like 333999333.33 to “333,999,999.33” in Haskell. Copes with negative numbers and rounds to 2 dp (easy to add a paramater for that should you wish).
Examples:
*Main> formatDecimal 44 "44.00" *Main> formatDecimal 94280943.4324 "94,280,943.43" *Main> formatDecimal (-89438.329) "-89,438.33"
import Data.Graph.Inductive.Query.Monad (mapFst) import List import Text.Printf formatDecimal d | d < 0.0 = "-" ++ (formatPositiveDecimal (-d)) | otherwise = formatPositiveDecimal d where formatPositiveDecimal = uncurry (++) . mapFst addCommas . span (/= '.') . printf "%0.2f" addCommas = reverse . concat . intersperse "," . unfoldr splitIntoBlocksOfThree . reverse splitIntoBlocksOfThree l = case splitAt 3 l of ([], _) -> Nothing; p-> Just p
If you know a simpler way or spot anything that should be done differently, please add a comment.