diff options
Diffstat (limited to 'src/Pool.hs')
| -rw-r--r-- | src/Pool.hs | 55 |
1 files changed, 55 insertions, 0 deletions
diff --git a/src/Pool.hs b/src/Pool.hs new file mode 100644 index 0000000..8bb40eb --- /dev/null +++ b/src/Pool.hs @@ -0,0 +1,55 @@ +-- 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) } |