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

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

• load is the core function to read a emacs lisp file. It takes a file name. And search load-path if the file is not full path.
• load-file is a wrapper to load. It provides some syntax shortcut.
• require calls load when the required symbol is not already loaded. [see Emacs Lisp: provide, require, features]
• autoload associates a symbol name (a function) with a file name. When the function is called and it's not already found in symbol table, it calls load to load the associated file and run the function.

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.

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:

• The file lisp-mode.el provides the symbol lisp-mode as feature, and is invoked by a command named emacs-lisp-mode.
• The cua-base.el file provides symbols cua-base and cua as features, and is invoked by a command named cua-mode.
• The text-mode.el file does not provide any symbol for feature. It is invoked by a command named text-mode.
• The file desktop.el provides the symbol desktop as feature, and the command name to invoke it is desktop-save-mode.

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.

• (info "(elisp) Loading")

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