Util/Set.hs

   1 module Util.Set where
   2 import qualified Data.List as List
   3 import Data.Maybe (fromJust)
   4 import Data.Set (Set)
   5 import qualified Data.Set as Set
   6 import Data.Tuple (swap)
   7
   8 subsetsOfSize :: Ord a => Integer -> Set a -> Set (Set a)
   9 subsetsOfSize n xs = case compare n 0 of
  10   LT -> Set.empty
  11   EQ -> Set.singleton Set.empty
  12   GT -> case Set.minView xs of
  13     Nothing -> Set.empty
  14     Just (x, xs') -> Set.union
  15       (subsetsOfSize n xs') $
  16       Set.map (Set.insert x) $ subsetsOfSize (n - 1) xs'
  17
  18 distinctPairsOneWay :: Ord a => Set a -> Set (a, a)
  19 distinctPairsOneWay =
  20   Set.map (\xys -> let [x, y] = Set.toList xys in (x, y)) . subsetsOfSize 2
  21
  22 distinctPairs :: Ord a => Set a -> Set (a, a)
  23 distinctPairs xs =
  24   let dpow = distinctPairsOneWay xs in
  25   Set.union dpow $ Set.map swap dpow
  26
  27 distinctTriplesOneWay :: Ord a => Set a -> Set (a, a, a)
  28 distinctTriplesOneWay =
  29   Set.map (\xyzs -> let [x, y, z] = Set.toList xyzs in (x, y, z))
  30   . subsetsOfSize 3
  31