set-comprehension.hs

{-# LANGUAGE MonadComprehensions #-}
{-# LANGUAGE OverloadedLists     #-}
{-# LANGUAGE RebindableSyntax    #-}

import           Data.Set (Set, singleton)
import           GHC.Exts
import           Prelude

xs :: Set Int
xs = [3, 15]

ys :: Set Int
ys = [9, 20]

zs :: Set Int
zs = [x + y | x <- xs, y <- ys]
  where
    return = singleton
    s >>= f = foldMap f s