-- | A /bit set/ maintains a record of members from a type that can be mapped -- into (non-negative) @Int@s. The maximum number of elements that can be -- stored is @maxbound :: Int@. Supports insertion, deletion, size, and -- membership testing, and is completely pure (functional). -- -- To use this library, simply supply a `Enum' instance for your data type or -- have it derived. It is important that the values you intend to keep track -- of start from 0 and go up. A value for which @fromEnum x@ is @n@ -- corresponds to bit location @n@ in an @Integer@, and thus requires that -- @Integer@ to have at least @n@ bits. -- -- The implementation is quite simple: we rely on the @Bits Integer@ instance -- from @Data.Bits@. An advantage of this library over simply using that -- @Bits@ instance is the phantom type parameter used in the `BitSet' type. -- The interface we expose ensures client code will not typecheck if it -- confuses two bit sets intended to keep track of different types. module Data.BitSet ( BitSet , empty , null , insert , fromList , delete , member , size ) where import Prelude hiding ( null ) import Data.Bits import Data.Data data BitSet a = BS {-# UNPACK #-} !Int {-# UNPACK #-} !Integer deriving (Eq, Ord, Data, Typeable) instance (Enum a, Show a) => Show (BitSet a) where show (BS _ i :: BitSet a) = "fromList " ++ show (f 0 i) where f _ 0 = [] f n x = if testBit x 0 then (toEnum n :: a) : f (n+1) (shiftR x 1) else f (n+1) (shiftR x 1) -- | The empty bit set. empty :: BitSet a -- | Is the bit set empty? null :: BitSet a -> Bool -- | /O(setBit on Integer)/ Insert an item into the bit set. insert :: Enum a => a -> BitSet a -> BitSet a -- | /O(n * setBit on Integer)/ Make a @BitSet@ from a list of items. fromList :: Enum a => [a] -> BitSet a -- | /O(clearBit on Integer)/ Delete an item from the bit set. delete :: Enum a => a -> BitSet a -> BitSet a -- | /O(testBit on Integer)/ Ask whether the item is in the bit set. member :: Enum a => a -> BitSet a -> Bool -- | /O(1)/ The number of elements in the bit set. size :: BitSet a -> Int -- * Implementation {-# INLINE empty #-} empty = BS 0 0 {-# INLINE null #-} null (BS n _) = n == 0 {-# INLINE insert #-} insert x (BS count i) = BS count' (setBit i e) where count' = if testBit i e then count else count+1 e = fromEnum x fromList xs = BS (length xs) (foldl (\i x -> setBit i (fromEnum x)) 0 xs) {-# INLINE delete #-} delete x (BS count i) = BS count' (clearBit i e) where count' = if testBit i e then count-1 else count e = fromEnum x {-# INLINE member #-} member x (BS _ i) = testBit i (fromEnum x) {-# INLINE size #-} size (BS count _) = count