a tiny (and slow) Burrows-Wheeler Transform in Haskell

BTW.hs

module BWT where

import Data.List (sort)

ibwt :: String -> String
ibwt s =
  let len = length s
      cs = cycle s in
    head $
    head $
    take 1 $
    drop (len-1) $
    iterate (sort . (zipWith (:) s)) $
    sort $
    map (:[]) s

bwt :: String -> String
bwt s =
  let len = length s
      cs = cycle s in
    map last $
    sort $
    take len $
    map (take len) $
    iterate (drop 1) cs

-- *BWT> bwt "\STXHello world"
-- "do\STXlHrellwo "
-- *BWT> ibwt "do\STXlHrellwo "
-- "\STXHello world"