prescient.el: simple but effective sorting and filtering for Emacs.

Summary

prescient.el is a library which sorts and filters lists of candidates, such as appear when you use a package like Ivy or Company. Extension packages such as ivy-prescient.el and company-prescient.el adapt the library for usage with various frameworks.

As compared to other packages which accomplish similar tasks, including IDO, Ivy, Helm, Smex, Flx, Historian, and Company-Statistics, prescient.el aims to be simpler, more predictable, and faster.

Installation

prescient.el is available on MELPA as four separate packages (one for the library, and the rest for integrating with other frameworks):

• prescient
• ivy-prescient
• company-prescient
• selectrum-prescient

The easiest way to install these packages is using straight.el:

(straight-use-package 'prescient)
(straight-use-package 'ivy-prescient)
(straight-use-package 'company-prescient)
(straight-use-package 'selectrum-prescient)

However, you may install using any other package manager if you prefer.

Usage

• To cause Ivy to use prescient.el sorting and filtering, enable ivy-prescient-mode.
• To cause Company to use prescient.el sorting, enable company-prescient-mode.
• To cause Selectrum to use prescient.el sorting and filtering, enable selectrum-prescient-mode.
• To cause your usage statistics to be saved between Emacs sessions, enable prescient-persist-mode.

Please note that you must load Counsel before ivy-prescient.el. This is because loading Counsel results in a number of changes being made to the user options of Ivy, which ivy-prescient.el must then undo.

The modes handle sorting and filtering by default. See the package specific sections for options to configure this.

Algorithm

prescient.el takes as input a list of candidates, and a query that you type. The query is first split on spaces into subqueries (two consecutive spaces match a literal space). Each subquery filters the candidates because it must match as either a substring of the candidate, a regexp, or an initialism (e.g. ffap matches find-file-at-point, and so does fa). The last few candidates you selected are displayed first, followed by the most frequently selected ones, and then the remaining candidates are sorted by length. If you don't like the algorithm used for filtering, you can choose a different one by customizing prescient-filter-method.

If you would like prescient.el to forget about a candidate, use the command prescient-forget.

Configuration and other features

• prescient-history-length: The number of recently selected candidates that are remembered and displayed at the top of the list.

• prescient-frequency-decay: prescient.el keeps a "frequency" for each selected candidate, which is incremented by one each time you select the candidate. To keep things tidy, frequencies are multiplied by this variable's value each time you select a new candidate, so they decrease over time.

• prescient-frequency-threshold: Once the frequency for an infrequently used command falls below the value of this variable, prescient.el forgets about it.

• prescient-save-file: Where to save statistics that are persisted between Emacs sessions when prescient-persist-mode is active. The default value follows the conventions of no-littering.

• prescient-filter-method: A list of algorithms to use for filtering candidates. The default is literal, regexp, and initialism as described above, but you can also use substring matching, initialism matching, regexp matching, fuzzy matching, prefix matching, anchored matching, literal-prefix matching, or any combination of those. See the docstring for full details.

• prescient-filter-alist: An alist of symbol-function pairs that associate a symbol in prescient-filter-method with a function that creates a regexp for matching a candidate. You can add to this alist to define your own custom filter methods, and use them by adding the appropriate symbol to prescient-filter-method.

• prescient-sort-full-matches-first: Whether prescient.el sorts candidates that are fully matched before candidates that are partially matched.

• prescient-use-char-folding: Whether the literal and literal-prefix filter methods use character folding.

• prescient-use-case-folding: Whether filtering methods use case folding (in non-Emacs terms, whether they are not case-sensitive). This can be one of nil, t, or smart (the default). If smart, then case folding is disabled when upper-case characters are sought.

Company-specific

• company-prescient-sort-length-enable: By default, the standard prescient.el sorting algorithm is used for all Company completions when company-prescient-mode is enabled. However, this algorithm is inappropriate in some situations. In particular, some Company backends return fuzzy-matched candidates with an intelligent sorting pre-applied. In this case, the fallback sorting by length that prescient.el does will just make a giant mess of things. By customizing this user option to nil for such Company backends (see Radian for an example), you can avoid the problem. Then prescient.el will helpfully move recently and frequently used candidates to the top of the completions list, but otherwise leave candidate ordering alone.

Ivy-specific

The following user options are specific to using prescient.el with Ivy:

• ivy-prescient-sort-commands: By default, all commands have their candidates sorted. You can override this behavior by customizing ivy-prescient-sort-commands. See the docstring.

• ivy-prescient-retain-classic-highlighting: By default, the highlighting behavior of ivy-prescient.el is slightly different from Ivy's highlighting for ivy--regex-ignore-order. You can recover the original behavior by customizing this user option; see the docstring for more details.

• ivy-prescient-enable-filtering: If set to nil, then ivy-prescient.el does not apply prescient.el filtering to Ivy. See the Ivy documentation for information on how Ivy filters by default, and how to customize it manually.

• ivy-prescient-enable-sorting: If set to nil, then ivy-prescient.el does not apply prescient.el sorting to Ivy. See the Ivy documentation for information on how Ivy sorts by default, and how to customize it manually.

Selectrum-specific

The following user options are specific to using prescient.el with Selectrum:

• selectrum-prescient-enable-filtering: If set to nil, then selectrum-prescient.el does not change filtering of Selectrum. See the Selectrum documentation for information on how Selectrum configures filtering by default, and how to customize it manually.

• selectrum-prescient-enable-sorting: If set to nil, then selectrum-prescient.el does not change sorting of Selectrum. See the Selectrum documentation for information on how Selectrum configures sorting by default, and how to customize it manually.

selectrum-prescient.el provides special commands (see the table below) to adjust how prescient.el filters candidates in the current Selectrum buffer.

For example, to toggle regexp filtering on or off (perhaps you're searching for a long/complex candidate), you can press M-s r. If you wish to use only regexp filtering, you can use C-u M-s r to unconditionally turn on regexp filtering and turn off all other methods. This toggling is a buffer-local effect, and does not change the default filter behavior. For that, customize prescient-filter-method.

These commands are similar in usage to Isearch's own toggling commands, except that multiple filtering methods can be active at the same time. While selectrum-prescient-mode is enabled, M-s is bound to selectrum-prescient-toggle-map in the Selectrum buffer, and is used as a prefix key to access the commands.

Key	Command
M-s a	selectrum-prescient-toggle-anchored
M-s f	selectrum-prescient-toggle-fuzzy
M-s i	selectrum-prescient-toggle-initialism
M-s l	selectrum-prescient-toggle-literal
M-s p	selectrum-prescient-toggle-prefix
M-s P	selectrum-prescient-toggle-literal-prefix
M-s r	selectrum-prescient-toggle-regexp
M-s '	selectrum-prescient-toggle-char-fold
M-s c	selectrum-prescient-toggle-case-fold

When defining custom filter methods, you can create new bindings using selectrum-prescient-create-and-bind-toggle-command, which takes an unquoted filter symbol and a string that can be used by kbd. For example,

(selectrum-prescient-create-and-bind-toggle-command my-foo "M-f")

will bind a command to toggle the my-foo filter to M-s M-f.

With selectrum-prescient-enable-filtering set, the part of each candidate that matches your input is highlighted with the face selectrum-prescient-primary-highlight. There is also selectrum-prescient-secondary-highlight for additional highlighting of specific matched parts of the input.

The following example shows customizing these faces, I use the Zerodark color theme, which includes colors for Ivy, but not for Selectrum. I inspected the theme source code to see what colors were being used for Ivy, and copied them to be used for Selectrum as well:

(require 'zerodark-theme)

(let ((class '((class color) (min-colors 89))))
  (custom-theme-set-faces
   'zerodark
   `(selectrum-current-candidate
     ((,class (:background "#48384c"
                           :weight bold
                           :foreground "#c678dd"))))
   `(selectrum-prescient-primary-highlight
   ((,class (:foreground "#da8548"))))
   `(selectrum-prescient-secondary-highlight
   ((,class (:foreground "#98be65"))))))

(enable-theme 'zerodark)

Contributor guide

Please see the contributor guide for my projects.