What I have so far... but doesn't quite work

kata.hs

module Codewars.Kata.SqIntoSq where

import Debug.Trace

decompose :: Integer -> Maybe [Integer]
decompose num = decomposer (num^2) (num-1)

decomposer :: Integer -> Integer -> Maybe [Integer]
decomposer total num =
  case (num, squareSum list == total) of
    (_, True)     -> Just list
    (0, _)        -> Nothing
    (num', False) -> decomposer total (num' - 1)
  where
    list = trace (show list') $ list' -- debug help
    list' = foldr reducer [] [1..num]
    squareSum = sum . fmap (^2)

    reducer n acc =
      if squareSum acc > total then
          reducer n (tail acc)
      else
          n : acc