* Overview
:PROPERTIES:
:TOC: :include all :ignore this
:END:

This package provides an =orderless= /completion style/ that divides the
pattern into space-separated components, and matches candidates that
match all of the components in any order. Each component can match in
any one of several ways: literally, as a regexp, as an initialism, in
the flex style, or as multiple word prefixes. By default, regexp and
initialism matches are enabled.

A completion style is a backend for completion and is used from a
frontend that provides a completion UI. Any completion style can be
used with the default Emacs completion UI (sometimes called minibuffer
tab completion) or with the built-in Icomplete package (which is
similar to the more well-known Ido Mode). To use a completion style in
this fashion simply add it as an entry in the variables
=completion-styles= and =completion-category-overrides= (see their
documentation).

With a bit of effort, it might still be possible to use =orderless= with
other completion UIs, even if those UIs don't support the standard
Emacs completion styles. Currently there is support for 
[[https://github.com/abo-abo/swiper][Ivy]] and 
[[https://github.com/raxod502/selectrum][Selectrum]] (see below).

If you use MELPA, the easiest way to install =orderless= is via
=package-install=. If you use both MELPA and =use-package=, you can use:

#+begin_src emacs-lisp
  (use-package orderless
    :ensure t
    :init (icomplete-mode) ; optional but recommended!
    :custom (completion-styles '(orderless)))
#+end_src

Alternatively, put =orderless.el= somewhere on your =load-path=, and use
the following configuration:

#+begin_src emacs-lisp
(require 'orderless)
(setq completion-styles '(orderless))
(icomplete-mode) ; optional but recommended!
#+end_src

(And of course, if you use another completion framework such as Ivy or
Helm, disable it.)

If you like the experience of using =orderless= with Icomplete, but wish
the candidates displayed vertically, you can use [[https://github.com/oantolin/icomplete-vertical][icomplete-vertical]].

Bug reports are highly welcome and appreciated!

:CONTENTS:
- [[#screenshot][Screenshot]]
- [[#customization][Customization]]
  - [[#component-matching-styles][Component matching styles]]
  - [[#component-separator-regexp][Component separator regexp]]
  - [[#faces-for-component-matches][Faces for component matches]]
- [[#related-packages][Related packages]]
  - [[#ivy-and-helm][Ivy and Helm]]
  - [[#prescient][Prescient]]
  - [[#icicless-progressive-matching][Icicles's progressive matching]]
- [[#integration-with-other-completion-uis][Integration with other completion UIs]]
  - [[#ivy][Ivy]]
  - [[#selectrum][Selectrum]]
:END:

** Screenshot

This is what it looks like to use =describe-function= (bound by default
to =C-h f=) to match =eis ff=. Notice that in this particular case =eis=
matched as an initialism, and =ff= matched as a regexp. The completion
UI in the screenshot is [[https://github.com/oantolin/icomplete-vertical][icomplete-vertical]] and the theme is
Protesilaos Stavrou's lovely [[https://gitlab.com/protesilaos/modus-themes][modus-operandi]].

[[images/describe-function-eis-ff.png]]

* Customization

** Component matching styles

Each component of a pattern can match in any of several matching
styles. A matching style is simply a function from strings to strings
that maps a component to a regexp to match against, so it is easy to
define new matching styles. The predefined ones are:

- orderless-regexp :: the component is treated as a regexp that must
  match somewhere in the candidate.

  This is simply the identity function!

- orderless-literal :: the component is treated as a literal string
  that must occur in the candidate.

  This is just =regexp-quote=.

- orderless-initialism :: each character of the component should appear
  as the beginning of a word in the candidate, in order.

  This maps =abc= to =\<a.*\<b.*\c=.

- orderless-flex :: the characters of the component should appear in
  that order in the candidate, but not necessarily consecutively.

  This maps =abc= to =a.*b.*c=.

- orderless-prefixes :: the component is split at word endings and
  each piece must match at a word boundary in the candidate, occurring
  in that order.

  This is similar to the built-in =partial-completion= completion-style.
  For example, =re-re= matches =query-replace-regexp=, =recode-region= and
  =magit-remote-list-refs=; =f-d.t= matches =final-draft.txt=.

The variable =orderless-component-matching-styles= should be set to a
list of the desired styles to use. By default it enables the regexp
and initialism styles.

** Component separator regexp

The pattern components are space-separated by default: this is
controlled by the variable =orderless-component-separator=, which should be
set to a regexp that matches the desired component separator. The
default value matches a sequence of spaces. It may be useful to add
hyphens or slashes (or both), to match symbols or file paths,
respectively.

If you are implementing a command for which you know you want a
different separator for the components, bind
=orderless-component-separator= in a =let= form.

The package also provides a command
=orderless-temporarily-change-separator= to change it for the rest of
the current completion session. If you want to use it, bind it to a
key in a keymap that will be active during your completion session:

- Icomplete users should bind it in =icomplete-minibuffer-map=.
- Users of the default completion should bind it in both
  =minibuffer-local-completion-map= and
  =minibuffer-local-filename-completion-map=.

** Faces for component matches

The portions of a candidate matching each component get highlighted in
one of four faces, =orderless-match-face-?= where =?= is a number from 0
to 3. If the pattern has more than four components, the faces get
reused cyclically.

If your =completion-styles= (or =completion-category-overrides= for some
particular category) has more than one entry, remember than Emacs
tries each completion style in turn and uses the first one returning
matches. You will only see these particular faces when the =orderless=
completion is the one that ends up being used, of course.

* Related packages

** Ivy and Helm

The well-known and hugely powerful completion frameworks [[https://github.com/abo-abo/swiper][Ivy]] and [[https://github.com/emacs-helm/helm][Helm]]
also provide for matching space-separated component regexps in any
order. In Ivy, this is done with the =ivy--regex-ignore-order= matcher.
In Helm, it is the default, called "multi pattern matching".

This package is significantly smaller than either of those because it
solely defines a completion style, meant to be used with the built-in
Icomplete completion UI, while both of those provide their own
completion UI (and many other cool features!).

It is worth pointing out that Helm does provide its multi pattern
matching as a completion style which could be used with Icomplete! (Ivy
does not.) So, Icomplete users could, instead of using this package,
install Helm and configure Icomplete to use it as follows:

#+begin_src emacs-lisp
  (require 'helm)
  (setq completion-styles '(helm))
  (icomplete-mode)
#+end_src

(Of course, if you install Helm, you might as well use the Helm UI in
=helm-mode= rather than Icomplete.)

** Prescient

The [[https://github.com/raxod502/prescient.el][prescient.el]] library also provides matching of space-separated
components in any order and it can be used with either the [[https://github.com/raxod502/selectrum][Selectrum]]
or [[https://github.com/abo-abo/swiper][Ivy]] completion UIs (it does not offer a completion-style that
could be used with Emacs' default completion UI or with Icomplete).
The components can be matched literally, as regexps, as initialisms or
in the flex style (called "fuzzy" in prescient). In addition to
matching, =prescient.el= also supports sorting of candidates (=orderless=
leaves that up to the candidate source and the completion UI).

** Icicles's progressive matching

An effect equivalent to matching multiple components in any order can
be achieved in completion frameworks that provide a way to restrict
further matching to the current lists of candidates. In [[https://www.emacswiki.org/emacs/Icicles][Icicles]] this
is called /progressive completion/ and using =S-SPC= instead of =SPC= to
separate components will do it. (Note that Ivy has an analogous
command, also bound to =S-SPC=, called =ivy-restrict-to-matches=, so you
can get the effect of out of order matching without using
=ivy--regex-ignore-order=.)

* Integration with other completion UIs

Several excellent completion UIs exist for Emacs in third party
packages. They do have a tendency to forsake standard Emacs APIs, so
integration with them must be done on a case by case basis.

If you manage to use =orderless= with a completion UI not listed here,
please file an issue or make a pull request so others can benefit from
your effort. The functions =orderless-filter=,
=orderless-highlight-matches=, =orderless--highlight= and
=orderless--component-regexps= are likely to help with the
integration.

** Ivy

To use =orderless= from Ivy add this to your Ivy configuration:

#+begin_src emacs-lisp
  (setq ivy-re-builders-alist '((t . orderless--ivy-re-builder)))
#+end_src

** Selectrum

To use =orderless= from Selectrum add this to your Selectrum
configuration:

#+begin_src emacs-lisp
  (setq selectrum-refine-candidates-function #'orderless-filter)
  (setq selectrum-highlight-candidates-function #'orderless-highlight-matches)
#+end_src