Elisp: require, load, load-file, autoload, feature

By Xah Lee. Date: . Last updated: .

Emacs lisp's library system is a primitive system, centered on loading file by load, with some slightly high level things such as its {features, autoload, require}. However, nothing is strict or enforced by elisp.

load

load → is the general function for loading a file.

Syntax is:

(load FILE &optional NOERROR NOMESSAGE NOSUFFIX MUST-SUFFIX)

If no optional argument is given, it'll try to load the FILE by searching for it in a list of directory stored in variable load-path, by first appending .elc to the argument FILE, and if none found, it'll try appending .el, and others, and finally try just FILE as given.

For example, if you

(load "x"), it'll first try

  1. x.elc
  2. x.el
  3. x

load-file

load-file → load one specific file. The file name argument should contain file name extension, such as .el .elc

(load-file file_name) just calls

(load (expand-file-name file_name) nil nil t)

Use load-file when you have a specific full path of a file in mind.

require

require → Load a package if it has not already been loaded.

(require FEATURE &optional FILENAME NOERROR)

require checks if the symbol FEATURE is in variable features. If not, then it calls load to load it.

File name is guessed from the feature name FEATURE, or specified in the optional argument.

require is best used in elisp libraries or scripts, similar to other language's “require” or “import”.

autoload

autoload → Load a file only when a function is called.

(autoload FUNCTION FILE &optional DOCSTRING INTERACTIVE TYPE)

autoload associates a function name with a file path. When the function is called, load the file, and execute the function.

If you are writing a major mode, have your package installation go by autoload if possible. It saves startup time.

See also: Elisp: How to Name Your Major Mode.

What's Library, Package, Feature?

No Namespace

Emacs lisp the language does not have namespace. Everything is global. So, don't expect library or module to be structured namespace like python module system or Java's Package system.

[see Python: How to Write a Module]

[see Java: Package]

What's the difference between a Package and Library?

These words are used losely, and do NOT have TECHNICAL definitions in elisp.

library → elisp file(s) containing a collection of useful stuff. For example, the command comment-dwim is defined in newcomment.el, which is a library of functions.

package → any useful elisp library for emacs users. For example: major mode or minor mode.

The term “module” is not used by emacs.

Emacs's Concept of Feature

Elisp: What's “feature”?

Package/Library/Feature are not Managed

There is no absolute relation between any concept of package/library/feature/autoload facilities and the file name.

By convention, if a elisp file name is xyz-mode.el, it OFTEN provides a lisp symbol “xyz-mode” as its feature name (if it does at all), and the command to invoke the mode is OFTEN named “xyz-mode”. Sometimes the “-mode” part is omitted in any of {file name, feature symbol name, command name}.

This is only a lose convention. There are a lot exceptions. For example:

All the above means, you could have a file named Joe-xyz-mode_v2.1.el, which provides a feature named “abc”, while the command name to activate it may be “opq”, and it might be displayed in mode line as “OPQ helper”. And, this file can be considered as a package or library.

Writing Major Mode

  1. How to Write a Emacs Major Mode for Syntax Coloring
  2. Elisp: html6-mode
  3. Elisp: Font Lock Mode Basics
  4. Elisp: How to Define Face
  5. Elisp: How to Color Comment in Major Mode
  6. Elisp: How to Write Comment Command in Major Mode
  7. Elisp: How to Write Your Own Comment Command from Scratch
  8. Elisp: How to Write Keyword Completion Command
  9. Elisp: How to Create Keymap for Major Mode
  10. Elisp: Abbrev, Template, for Major Mode
  11. Elisp: Text Properties
  12. Elisp: Overlay Highlighting
  13. Emacs: Lookup Google, Dictionary, Documentation
  14. Elisp: Syntax Table Tutorial

  1. Elisp: How to Name Your Major Mode
  2. Elisp: What's “feature”?
  3. Elisp: require, load, load-file, autoload, feature

Syntax Table

  1. Elisp: Syntax Table Tutorial
  2. Elisp: How to Find Syntax of a Character?
  3. Elisp: How to Modify Syntax Table Temporarily
  4. Elisp: How to Determine If Cursor is Inside String or Comment
  5. Elisp: Regex Patterns and Syntax Table
  6. Elisp: Find Matching Bracket Character
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