Solution to exercise 2 in section 8.7 in PureScript by Example

Sums.purs

module Sums where

import Data.Array ((:), foldM, nub, sort)
import Data.Maybe (Maybe(..))
import Prelude (($), (+), (++), map)

-- Given an array of integers, compute the list of all
-- possible totals, using each integer at most once.

sums :: Array Int -> Maybe (Array Int)
sums = foldM (\a e -> Just $ sort $ nub $ (e :) $ map (+e) a ++ a) [0]