ナムドット問題 ref: http://qiita.com/nobsun/items/b3341bb7fea43ff2bba7

numdot.hs

module Main where

import Data.List

main :: IO ()
main = putStr
     $ unlines
     $ map (intercalate ".")
     $ map (map reverse)      -- 部分文字列反転
     $ unravels 
     $ reverse                -- 入力文字列反転
     $ "12345"

unravels  ::  [a] ->  [[[a]]]
unravels  =   foldr (concatMap . uprefixes) [[]]

uprefixes             ::  a -> [[a]] -> [[[a]]]
uprefixes x []        =   [[[x]]]
uprefixes x (xs:xss)  =   ((x:xs):xss) : map (xs:) (uprefixes x xss)