Data.Vector.Algorithms.AmericanFlag

This module implements American flag sort: an in-place, unstable, bucket sort. Also in contrast to radix sort, the values are inspected in a big endian order, and buckets are sorted via recursive splitting. This, however, makes it sensible for sorting strings in lexicographic order (provided indexing is fast).

The algorithm works as follows: at each stage, the array is looped over, counting the number of elements for each bucket. Then, starting at the beginning of the array, elements are permuted in place to reside in the proper bucket, following chains until they reach back to the current base index. Finally, each bucket is sorted recursively. This lends itself well to the aforementioned variable-length strings, and so the algorithm takes a stopping predicate, which is given a representative of the stripe, rather than running for a set number of iterations.