Haskell library to convert unsigned integers to and from base36 representations

base36.hs

-- Converts unsigned integers to and from base36 representations

module Numeric.Base36 (
      readBase36
    , showBase36
    ) where

import Data.Char (isAscii, isLetter, isDigit, ord, chr, toLower)
import Numeric (readInt, showIntAtBase)

readBase36 :: (Integral a) => String -> [(a, String)]
readBase36 = readInt 36 isAsciiAlphaNum digitToInt

showBase36 :: (Integral a, Show a) => a -> String -> String
showBase36 = showIntAtBase 36 intToDigit

isAsciiAlphaNum :: Char -> Bool
isAsciiAlphaNum c = isAscii c && (isDigit c || isLetter c)

-- Slightly modified from the hexadecimal implementation in Data.Char
digitToInt :: Char -> Int
digitToInt c
    | isDigit c            =  ord c - ord '0'
    | c >= 'a' && c <= 'z' =  ord c - ord 'a' + 10
    | c >= 'A' && c <= 'Z' =  ord c - ord 'A' + 10
    | otherwise            =  error ("Base36.digitToInt: not a digit " ++ show c) -- sigh

intToDigit :: Int -> Char
intToDigit n
    | n < 10    = chr (n + ord '0')
    | otherwise = chr (n + ord 'a' - 10)

(78857554403044).toString(36)

Another win for JavaScript! (p.s. parseInt that with radix 36)