perfecthash: A perfect hashing library for mapping bytestrings to values.

[ bsd3, data, data-structures, library ] [ Propose Tags ]

A perfect hashing library for mapping bytestrings to values. Insertion is not supported (by design): Only fromList and lookup operations are supported. CI at

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Versions [faq] 0.2.0
Dependencies array, base (>=4.5 && <5.2), bytestring, cmph, containers, time [details]
License BSD-3-Clause
Author Mark Wotton <>
Maintainer Mark Wotton <>
Category Data, Data Structures
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Source repo head: git clone
Uploaded by MarkWotton at 2016-05-02T13:17:56Z
Distributions NixOS:0.2.0
Downloads 654 total (4 in the last 30 days)
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Status Hackage Matrix CI
Docs not available [build log]
All reported builds failed as of 2016-11-26 [all 3 reports]


  • Data
    • Data.PerfectHash


Maintainer's Corner

For package maintainers and hackage trustees

Readme for perfecthash-0.2.0

[back to package description]
This is an immutable hashtable built on cmph.

The motivation is mostly speed, and wren thornton's bytestring-trie seems to be the main competition:

% ./dist/build/benchmark_trie/benchmark_trie
* trie lookup:   1.136ns per iteration / 880403.98 per second.

% ./dist/build/benchmark/benchmark          
* perfect lookup:   0.687ns per iteration / 1456455.69 per second.

it also uses less space in the haskell heap, building once and doing the same number of lookups:

	total alloc = 2,525,223,964 bytes  (excludes profiling overheads)

	total alloc = 9,806,202,096 bytes  (excludes profiling overheads)

although this is not an entirely fair comparison given how much PerfectHash stores on the C side.