Easy: http://hackage.haskell.org/package/recursion-2.2.4.0/docs/Control-Recursion.html#v:zygo http://hackage.haskell.org/package/recursion-2.2.4.0/docs/Co... A

Easy: http://hackage.haskell.org/package/recursion-2.2.4.0/docs/Control-Recursion.html#v:zygo http://hackage.haskell.org/package/recursion-2.2.4.0/docs/Co... Also: subsets = filterM (pure [True, False])