Known-set implementation in PureScript

Main.purs

module Main where

import Prelude
import Data.Set as S
import Control.Monad.Eff (Eff)
import Control.Monad.Eff.Console (CONSOLE, log)
import Data.Set (Set, empty)

type Task = Int
type Spawns = Set Task

data Tree = Leaf Spawns | Branch Tree Tree

type KnownSet = {spawns:: Spawns, joins:: Tree}

make :: KnownSet
make = {spawns: S.empty, joins: Leaf S.empty}

set_copy :: Spawns -> Spawns
set_copy x = x 

copy :: KnownSet -> KnownSet
copy ks = {
  spawns: S.empty,
  joins: Branch (Leaf (set_copy ks.spawns)) ks.joins
}

add :: KnownSet -> Task -> KnownSet
add ks x = {spawns: S.insert x ks.spawns, joins: ks.joins }

contains :: KnownSet -> Int -> Boolean
contains ks x = x `S.member` ks.spawns || isIn ks.joins
  where
  isIn :: Tree -> Boolean
  isIn (Leaf s) = x `S.member` s
  isIn (Branch l r) = isIn l || isIn r  

union :: KnownSet -> Tree -> KnownSet
union ks j = {spawns: ks.spawns, joins: Branch j ks.joins}

main :: forall e. Eff (console :: CONSOLE | e) Unit
main = do
  log (show (contains (add (copy (add make 1)) 2) 2))