Concatenate the square of all the digits of a number
Separate out combinators that apply some perspective to your data.

squareDigit = overAbs $ overDigits $ concatMap $ digs . (^ 2) where
  overAbs f n = signum n * f (abs n)
  overDigits f = foldl (\acc x -&gt; x + (acc * 10)) 0 . f . digs