bitset

A bit set is a compact data structure, which maintains a set of members from a type that can be enumerated (i. e. has an Enum instance). Current implementation is abstract with respect to conatiner type, so any numeric type with Bits instance can be used as a container. However, independent of container choice, the maximum number of elements in a bit set is bounded by maxBound :: Int.

Here's a usage example for a dynamic bit set, which uses Integer for storing bits:

import Data.BitSet (BitSet, (\\))
import qualified Data.BitSet as BitSet

data Color = Red | Green | Blue deriving (Show, Enum)

main :: IO ()
main = print $ bs \\ BitSet.singleton Blue where
  bs :: BitSet Color
  bs = BitSet.fromList [Red, Green, Blue]

The API is exactly the same for a static bitset, based on native Word. Here's an example from [hen] hen library, which uses Data.BitSet to store Xen domain status flags:

import qualified Data.BitSet.Word as BS

data DomainFlag = Dying
                | Crashed
                | Shutdown
                | Paused
                | Blocked
                | Running
                | HVM
                | Debugged
    deriving (Enum, Show)

isAlive :: DomainFlag -> Bool
isAlive = not . BS.null . BS.intersect (BS.fromList [Crashed, Shutdown])

Benchmarks

To run benchmarks benchmarks, configure cabal with benchmarks and build:

$ cabal-dev install-deps --enable-benchmarks && cabal-dev build
$ ./dist/build/bitset-benchmarks/bitset-benchmarks -o dist/bench.html