Give Emacs Psychic Completion Powers with prescient.el

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Completions are everywhere

  • M-x
  • describe-variable / describe-function
  • find-file
  • switch-to-buffer
  • company-mode

It saves time to make the list of recommendations more tailored to your usage!

Enter prescient.el

Prescient is a sorting and filtering extension for Ivy, company-mode, and Selectrum. It provides:

  • Sorting candidates based on how frequently you select them
  • Configurable filtering rules to quickly find what you’re looking for


Since we’ve been using Ivy in the configuration for this channel, let’s try Prescient with it.

First, try M-x without Prescient turned on, then install ivy-prescient (make sure to load it after Counsel!)

(use-package ivy-prescient
  :after counsel
  (ivy-prescient-mode 1))

Now run M-x again and take a look at the results. Select a command, then run M-x again, see that it is suggested first!

Prescient is remembering the selections you’ve made for M-x (or counsel-M-x in this case) and it sorts them first based on some configurable rules:

  • prescient-history-length: How many chosen candidates will be remembered
  • prescient-frequency-decay: A multiplier applied to each frequent candidate each selection (default: 0.997)
  • prescient-frequency-threshold: Threshold used for “forgetting” a command that isn’t used frequently anymore (default: 0.5)

NOTE: These variables apply to all usages of Prescient, not just for Ivy!

Trying Prescient with other Ivy commands

  • counsel-find-file
  • counsel-describe-variable
  • counsel-switch-buffer - Doesn’t work!

Excluding certain Ivy commands from sorting

  • Commands to exclude: ivy-prescient-sort-commands

By default it contains ivy-switch-buffer which counsel-switch-buffer uses internally.

Disabling length-based sorting

You might have noticed M-x is now sorting all commands by shortest-first. If this is distracting to you, it can be disabled!

(setq prescient-sort-length-enable nil)

Changing the filtering method

Set prescient-filter-method:

;; This is the default value!
(setq prescient-filter-method '(literal regexp fuzzy))
  • literal: the subquery must be a substring of the candidate. Supports char folding.
  • initialism: the subquery must match a substring of the initials of the candidate.
  • prefix: words (substrings of only word characters) match the beginning of words found in the candidate, in order, separated by the same non-word characters that separate words in the query. This is similar to the completion style partial or what you get from Ivy by default
  • anchored: words are separated by capital letters or symbols, with capital letters being the start of a new word. This is similar to prefix, but allows for less typing.
  • fuzzy: the characters of the subquery must match some subset of those of the candidate, in the correct order but not necessarily contiguous.
  • regexp: the subquery is interpreted directly as a regular expression. (Try ^p\w+d)

Going back to Ivy’s filtering

If you are too used to Ivy’s filtering styles, you can use those while still keeping Prescient’s sorting:

(setq ivy-prescient-enable-filtering nil)

NOTE: Make sure you toggle ivy-prescient-mode after setting this for it to take effect!

Getting the old highlighting back

ivy-prescient changes how results are highlighted when you start typing. To emulate the old highlighting you can use ivy-prescient-retain-classic-highlighting:

(setq ivy-prescient-retain-classic-highlighting t)

Company Mode

Prescient also has an extension for Company to provide candidate sorting based on frequency:

(use-package company-prescient
  :after company
  (company-prescient-mode 1))

NOTE: Prescient filtering is not applied to company-mode! It would require a custom completion backend.

Remembering history between sessions

Remembering your history is great, but it’s even better when it is remembered each time you start Emacs:

;; Remember candidate frequencies across sessions
(prescient-persist-mode 1)

With all that said…

ivy-prescient needs a new maintainer:

If you like using Prescient with Ivy, consider helping out!


We will talk about Selectrum in another video; we’ll hook it up to Prescient then!

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