An efficient finite map from (byte)strings to values.
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README.md

bytestring-trie

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The bytestring-trie package provides an efficient implementation of tries mapping ByteString to values. Actually, it provides two implementations:

The old implementation (prior to version 0.3) is based on Okasaki's big-endian patricia trees, à la IntMap. We first trie on the elements of ByteString and then trie on the big-endian bit representation of those elements. Patricia trees have efficient algorithms for union and other merging operations, but they're also quick for lookups and insertions.

The new implementation (since version 0.3) replaces the big-endian patricia trees with Bagwell's AMTs (array mapped tries), which are the precursor to the HAMTs used by the hashmap library. This implementation is still a work in progress, but once completed will replace the old implementation.

If you are only interested in being able to associate individual ByteStrings to values, then you may prefer the hashmap package which is faster for those only needing a map-like structure. This package is intended for those who need the extra capabilities that a trie-like structure can offer (e.g., structure sharing to reduce memory costs for highly redundant keys, taking the submap of all keys with a given prefix, contextual mapping, extracting the minimum and maximum keys, etc.)

Note that the GitHub repository is just a clone of the Darcs repo. I'm testing out whether to switch things over to GitHub in order to use TravisCI, and an official ticket tracker, etc.

Install

This is a simple package and should be easy to install. You should be able to use one of the following standard methods to install it.

-- With cabal-install and without the source:
$> cabal install bytestring-trie

-- With cabal-install and with the source already:
$> cd bytestring-trie
$> cabal install

-- Without cabal-install, but with the source already:
$> cd bytestring-trie
$> runhaskell Setup.hs configure --user
$> runhaskell Setup.hs build
$> runhaskell Setup.hs haddock --hyperlink-source
$> runhaskell Setup.hs copy
$> runhaskell Setup.hs register

The Haddock step is optional.

Portability

An attempt has been made to keep this library relatively portable. The old implementation is quite portable, relying only on a few basic language extensions. However, the new implementation relies on a number of GHC-specific language extensions (namely MagicHash and UnboxedTuples) in order to fully optimize things. The complete list of extensions used is:

  • BangPatterns - BangPatterns are supported in GHC as far back as version 6.6.1, and are also supported by JHC and UHC. As of 2010, they were not supported by Hugs; but alas Hugs is pretty much dead now.
  • CPP
  • ForeignFunctionInterface
  • MagicHash
  • NoImplicitPrelude
  • Rank2Types
  • UnboxedTuples

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