The dlist package

[ Tags: bsd3, data, library ] [ Propose Tags ]

Difference lists are a list-like type supporting O(1) append. This is particularly useful for efficient logging and pretty printing (e.g. with the Writer monad), where list append quickly becomes too expensive.

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Versions 0.2, 0.3, 0.3.1, 0.3.2, 0.4, 0.4.1, 0.5, 0.6,, 0.7,, 0.7.1,,, 0.8,,,
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Dependencies base (==4.*), deepseq (>=1.1 && <2) [details]
License BSD3
Copyright 2006-2009 Don Stewart, 2013-2016 Sean Leather
Author Don Stewart
Maintainer Sean Leather <>
Category Data
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Source repository head: git clone git://
Uploaded Tue Jul 4 14:02:50 UTC 2017 by SeanLeather
Distributions Arch:, Debian:, Fedora:, FreeBSD:, LTSHaskell:, NixOS:, Stackage:, Tumbleweed:
Downloads 285905 total (3413 in the last 30 days)
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Status Docs available [build log]
Last success reported on 2017-07-04 [all 1 reports]
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Difference Lists in Haskell

Hackage Hackage dependencies Travis CI


The Haskell dlist package defines a list-like type supporting O(1) append and snoc operations.

See for recent changes.



  1. A novel representation of lists and its application to the function “reverse.” John Hughes. Information Processing Letters. Volume 22, Issue 3. 1986-03. Pages 141-144. [PDF]

    This is the original source for a representation of lists as first-class functions.

Basic Introduction

  1. Difference list. Wikipedia.

  2. Difference lists. Wiki.

  3. What is a DList?. Stack Overflow.

Blogs and Discussion

  1. Using Difference Lists. Douglas M. Auclair. 2008-08-13.

  2. A Sort of Difference. Edward Kmett. 2008-09-18.

  3. Reference for technique wanted. Richard O'Keefe, et al. 2010-10-31.

  4. 24 Days of Hackage: dlist. Oliver Charles. 2012-12-14.

  5. Constructing a list in a Monad. Joachim Breitner. 2013-11-13.

  6. Demystifying DList. (On Reddit). Tom Ellis. 2014-01-24.

  7. keepEquals with Difference Lists, Douglas M. Auclair. 2014-06-21.


  1. Chapter 13. Data Structures. Real World Haskell. 2008-12-05.