GNU-devel ELPA: dash

A modern list API for Emacs.

Dash is a utility library that affords functional programming
patterns inspired by Clojure, particularly in the realm of list
manipulation.  Examples include higher-order functions (map, reduce,
filter) and derivatives (drop, flatten, sum); function combinators
(partial application, argument flipping, composition); and threading
and anaphoric macros with destructuring support.

Dash is particularly useful in providing a broad and consistent API
across many Emacs versions.

Documentation and examples are in the manual at Info node `(dash) Top'
and on the web at https://elpa.gnu.org/packages/doc/dash.html, as well
as in the project’s README.md file.

Dash NEWS -- history of user-visible changes

Copyright (C) 2012-2026 Free Software Foundation, Inc.

See the end of the file for license conditions.

Change log

From 2.20.0 to ?.?.?

Fixes

• The -cycle function is no longer marked as pure, as it returns a copy of its argument (#405).

From 2.19.1 to 2.20.0

Deprecations

• Calling -zip with two arguments now emits a warning. This long-discouraged calling convention remains supported, but the caller is now referred to the equivalent -zip-pair instead (Stefan Monnier, #400).
• Calling -zip-pair with less than or more than two arguments is now deprecated, and can be replaced with the equivalent call to -zip-lists instead.

Fixes

• Fixed a regression from 2.18 in -take that caused it to prematurely signal an error on improper lists (#393).
• The function -pad can now be called with zero lists as arguments.
• The functions -union, -intersection, and -difference now return proper sets, without duplicate elements (#397).

• The functions -same-items? and -permutations now work on multisets (lists with duplicate elements) (#390, #397, #399).

  For example:

  (-same-items? '(1 1 2 3) '(3 1 2)) ; => t
  (-permutations '(1 1 2)) ; => '((1 1 2) (1 2 1) (2 1 1))
  

• Several functions which are documented as returning a fresh, mutable object (such as a copy of one of their arguments) are no longer marked as pure. Pure functions called with constant arguments are evaluated during byte-compilation; the resulting value is an immutable constant, and thus unsafe to modify destructively. The functions in question are: -clone, -cons*, -drop-last, -interleave, -interpose, -iota, -non-nil, -repeat, -slice, -snoc, -split-at, -take, -take-last (#405).

New features

• The function -contains? now returns the matching tail of the list instead of just t, similarly to member (#397).
• New function -frequencies that takes a list and counts how many times each distinct element occurs in it (suggested by @ebpa, #209, #214, #399).
• New functions -zip-lists-fill and -unzip-lists which are better-behaved versions of -zip-fill and -unzip, respectively (#400).

From 2.19.0 to 2.19.1

Fixes

• Fixed a regression from 2.18 in -is-suffix-p which led to false negatives when parts of the suffix appeared multiple times in the list being searched (Bennett Rennier, #384).

From 2.18.1 to 2.19.0

Fixes

• Reverted a breaking change introduced in 2.18.0 that caused the threading macro --> to be indented differently from -> and ->> (#375).
• Added and fixed Edebug specifications for many Dash macros (Philipp Stephani, #380, #381).

New features

• The combinators -on, -flip, -not, -andfn, and -orfn now return variadic functions that take any number of arguments (#308).
• New combinator -rotate-args similar to -flip, but for arbitrary arglist rotations (suggested by @vapniks, #72).
• New function -every and its anaphoric macro counterpart --every. They are like the existing -every-p and --every-p, respectively, but return the last non-nil result instead of just t.
• New macro --partition-after-pred which affords -partition-after-pred better performance (Per Weijnitz, #362).

From 2.18.0 to 2.18.1

• Fixed a regression from 2.17 as well as a long-standing bug in --iterate, which evaluated its arguments one too many times. This in turn could lead to errors in -flatten-n when it tried flattening certain structures too far (#373).

From 2.17 to 2.18

This release absorbs the now obsolete dash-functional version 1.3.0 into dash, and brings the very old version of dash on GNU ELPA up to date.

Package maintainers should replace all uses of dash-functional, which will eventually be deleted, with dash version 2.18.0. For more information on this, see: ... ...