bitvec (hackage): A newtype over Bool with a better Vector instance: 8x less memory, up to 1000x faster.  The vector package represents unboxed arrays of Bools spending 1 byte (8 bits) per boolean. This library provides a newtype wrapper Bit and a custom instance of an unboxed Vector, which packs bits densely, achieving an 8x smaller memory footprint. The performance stays mostly the same; the most significant degradation happens for random writes (up to 10% slower). On the other hand, for certain bulk bit operations Vector Bit is up to 1000x faster than Vector Bool.  Data.Bit is faster, but writes and flips are thread-unsafe. This is because naive updates are not atomic: they read the whole word from memory, then modify a bit, then write the whole word back.  Data.Bit.ThreadSafe is slower (usually 10-20%), but writes and flips are thread-safe.  bv and bv-little do not offer mutable vectors.  array is memory-efficient for Bool, but lacks a handy Vector interface and is not thread-safe.
Keywords: bit-vectors|bsd3|data|library|public-domain|bit-array|bitmap|bitmask|libgmp|vectors