For Practice

base64encode.hs

{-# LANGUAGE ScopedTypeVariables #-}

module Main (main) where

import Data.List()
import Data.String()
import Data.List.Split
import Data.Function
import Data.Maybe
import System.Environment

main = do
    args <- getArgs
    putStrLn $ base64encode $ head args

intToBase64 = (fromJust.) $ flip lookup $ zip [0..63] "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/"
base64ToInt = (fromJust.) $ flip lookup $ zip "ABCDEFGHIJKLMNOPQRSTUVWXYZabcdefghijklmnopqrstuvwxyz0123456789+/" [0..63] 

base64encode :: String -> String
base64encode  = concatMap translate . chunksOf 6 . concatMap (toBits8 . fromEnum)

translate x = 
    (intToBase64 . binToInt) x : case length x of
    2 -> "=="
    4 -> "="
    6 -> ""

binToInt :: [Bool] -> Int
binToInt = sum . mulWeight . map fromEnum
    where
        mulWeight = map (\(i,x)->x * 2^i) . zip [0..] . reverse


boolToString :: Bool -> String
boolToString True = "1"
boolToString False = "0"

toBitsBySize :: forall a t. (Integral t, Integral a) => t -> a -> [Bool]
toBitsBySize 0 x = []
toBitsBySize sz 0 = [False | i <- [1..sz]]
toBitsBySize sz x =  if k == 0 
    then False : toBitsBySize n x
    else True  : toBitsBySize n (x - k*m)
    where n = sz - 1
          m = 2^n
          k = x `div` m

toBits8 = toBitsBySize 8