@hackage byte-containers0.1.0.0

This library provides variant of Data.Map and Data.Set from the containers library where the key is specialized to Word8. Internally, this uses a 256-bit bitmask for the presence of keys and a SmallArray of values of keys that were present. For example, the map {2 => Z, 3 => B, 5 => X, 9 => A} would be repsented in memory as:

Bitmask: 0011010001000000... (240 more zero bits)
Value Array: Z,B,X,A

This is optimized for reads. Lookup is O(1). Union is technically O(1) but only because the universe of keys is finite. The current implementation always scans through all 256 bits of key space.