This is a Haskell module to do Huffman coding. It is intended to be fairly generic and a good base for experimentation.

Included are file compression and decompression utilities that exercises the codebase. Performance is slower than but comparable to bzip2. On my home box (Intel Core 4) bzip2 takes 100ms to compress the text of Moby Dick, producing a 389KB file from a 1276KB original. My hencode utility takes 340ms to compress this file, producing a 740KB compressed file. Decompression with hdecode takes 190ms seconds, vs 40ms for bzip2.

The plan for this program was to enhance the Huffman code module such that it ccould be used as a basis for an implementation of inflate/deflate compression (RFC 1951), which is essentially Huffman coding plus LZ77 compression. This, in turn, can easily be wrapped into a ZLIB implementation (RFC1950), and will facilitate an implementation of the PNG image compression standard (RFC 2083 describes an earlier version).

However, it turned out that somebody had already implemented inflate/deflate in pure Haskell on hackage, which was cool. Work on the PNG implementation was abandoned long ago.

A good practical reference for Huffman coding tricks is Schindler's webpage. Adaptive Huffman coding also looks interesting.

This program is licensed under the "3-clause ('new') BSD License". Please see the file COPYING in this distribution for license terms.