Special Lisp Functions

• Special cases of functions: inline, macros, primitives, special forms, (keystroke) commands, byte-code functions.
• Inline functions: use defsubst instead of defun in the function definition.
• They can be used just like functions after they are declared, but they can speed up the program.
• Macro: defined like a function with defmacro instead of defun, but instead of computing a value, it computes another Lisp expression which in turn computes the value.
• The expression is called the expansion of the macro.
• Macros can simulate functions with reference parameters, but large macros can be difficult to write.

Built-in Functions

• Primitive - A function written in C that can be called from Lisp. It becomes a built-in function or a subr. One can add their own primitives to Emacs but Emacs must be recompiled to add them.
• Special form – a function that doesn't evaluate all the arguments the usual way.
• Example: the conditional.
  (if cond then-expr else-expr1 else-expr2 ...)
• If the condition has the value nil, then the then-expr is not evaluated at all.

Commands

• A command is a function that can be invoked interactively with command-execute or interactively with M-x.
• A keystroke command is a command that can be invoked with a combination of keys.
• A command also works as a regular function and can be called from anywhere.
• For a function to be a command, it must contain a call to the function interactive as the first expression in its definition.

Examples of Commands

(defun move2 ()
  (interactive)
  (forward-word 2))
(defun move-line (L)
  (interactive "nNr of lines:")
  (forward-line L))

• In the second function the argument in the call to interactive means that the first argument will be input from the user (minibuffer) and the text "Nr of lines:" will be displayed in the operation.
• More examples here

Buffers in Emacs

• When writing commands, it might be useful to access the current buffer, or selected region in the current buffer.
• A buffer is a Lisp object. The current buffer can be obtained by calling the function (current-buffer).
• Some useful information about the buffer: buffer-name, buffer-modified-p.
• Some operations to be done on buffers:
  kill-buffer, save-buffer, et.

Examples

(defun save-all ()
  (interactive)
  (let ((BL (buffer-list)))
    (mapc 'save-buffer BL)))

(setq B (current-buffer))
#<buffer macro.el>
(buffer-name B)
"macro.el"
(buffer-modified-p B) ; t
(save-buffer B) ; nil

Customizing Emacs

• There are a number of global variables that Emacs uses to define its functionality.
• For example, lisp-interactive-mode.
• Emacs will automatically load the file .emacs from your home directory at startup. Any global variables whose value is set in this file will determine a customization for the editor.

  (setq require-final-newline t)
  (set-background-color "black")
  (custom-set-variables '(indent-tabs-mode nil))