Emacs Lisp: load, load-file, autoload, require

By Xah Lee. Date: . Last updated: .

here's a summary of emacs lisp file loading system.

load
(load FILE &optional NOERROR NOMESSAGE NOSUFFIX MUST-SUFFIX)
The general function for loading a file.
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 try
  1. x.elc
  2. x.el
  3. x
load-file
Load one specific file. Use this when you have a specific full path of a file in mind. The file name argument should contain file name extension, such as .el or .elc.
(load-file file_name) just calls (load (expand-file-name file_name) nil nil t).
autoload
(autoload FUNCTION FILE &optional DOCSTRING INTERACTIVE TYPE)
Load a file only when a function is called. 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.

What is the difference between a Package and Library?

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

package
Usually refers to elisp files useful for emacs users. E.g. Command js-mode in js.el.
library
Usually means elisp files useful to emacs lisp coders. e.g. the function seq-drop is defined in seq.el, which is a library of functions.

The term “module” is not used by emacs.

No Namespace

Note: There is no structured mapping of “package/module/library” namespace and dir/file names. Emacs lisp does not have namespace, everything is global.

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.

emacs library/package system

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Elisp Write Major Mode

Basics

Package Name/Load

Syntax Table