1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
30
31
32
33
34
35
36
37
38
39
40
41
42
43
44
45
46
47
48
49
50
51
52
53
54
55
|
-- Copyright 2020 Google LLC
--
-- Licensed under the Apache License, Version 2.0 (the "License"); you may not
-- use this file except in compliance with the License. You may obtain a copy of
-- the License at
--
-- https://www.apache.org/licenses/LICENSE-2.0
--
-- Unless required by applicable law or agreed to in writing, software
-- distributed under the License is distributed on an "AS IS" BASIS, WITHOUT
-- WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied. See the
-- License for the specific language governing permissions and limitations under
-- the License.
{-# OPTIONS_GHC -Wno-missing-import-lists #-}
module Pool
( Pool
, empty, withReserved
, null
, take, put
) where
import Prelude hiding (null, take)
import Control.Monad (guard)
import qualified Data.List as List
import Data.Set (Set)
import qualified Data.Set as Set
data Pool a = Pool { reserved :: Set a, taken :: Set a } deriving (Eq, Show)
empty :: Pool a
empty = withReserved Set.empty
withReserved :: Set a -> Pool a
withReserved xs = Pool { reserved = xs, taken = Set.empty }
null :: Pool a -> Bool
null p = Set.null (taken p)
take :: (Bounded a, Enum a, Ord a) => Pool a -> Maybe (a, Pool a)
take p = do
x <- nextAvailable p
return (x, p { taken = Set.insert x (taken p) })
nextAvailable :: (Bounded a, Enum a, Ord a) => Pool a -> Maybe a
nextAvailable p = List.find (`Set.notMember` unavailable p) (enumFrom minBound)
unavailable :: (Ord a) => Pool a -> Set a
unavailable p = reserved p `Set.union` taken p
put :: Ord a => a -> Pool a -> Maybe (Pool a)
put x p = do
guard $ x `Set.member` taken p
return $ p { taken = Set.delete x (taken p) }
|