split integer.

split_int.hs

import System.Environment
import Data.List (intersperse)

split :: Int -> [[Int]]
split x = go x 1
  where
    go 0 _ = [[]]
    go n i = flip concatMap [i..n] $ \i' ->
                    map (i':) $ go (n-i') i'

format :: Int -> [Int] -> String
format n l = (show n) ++ "=" ++ intersperse '+' (concatMap show l)

main = do
    [n'] <- getArgs
    let n=read n'
    mapM_ putStrLn $ map (format n) $ filter ((>1) . length) $ split n
{-

> ./Main 4
4=1+1+1+1
4=1+1+2
4=1+3
4=2+2

-}