Writing GNU Emacs Extensions

Data Types

Numbers

Emacs Lisp supports integers and floating-point numbers. They're written in just the way you'd expect: as a string of base-10 digits with an optional leading minus sign and optional decimal point. Some functions that operate on numbers are:

(numberp x)

Test whether x is a number.

(integerp x)

Test whether x is an integer.

(zerop x)

Test whether x is zero.

(= a b)

Test whether two numbers are equal.

(+ a b c … )

Addition.

(- a b c … )

Subtraction.

Characters

Single characters can be written in Emacs Lisp by preceding them with a question mark. For instance, ?a denotes lowercase a. Some special characters, particularly those that can be used to begin other kinds of Lisp expression, must be preceded with question mark-backslash, such as ?\", ?\(, and ?\). Some special characters can be written by combining a backslash with a letter. For instance, ?\t is a tab character, and ?\n is a newline character.

The result of evaluating a character is its ASCII code. For instance, evaluating ?a yields 97. In fact, integers can be used wherever characters are expected; Emacs Lisp does not distinguish between the two, except to allow the more convenient form of denoting characters.

(char-equal a b)

Test whether two characters are equal. Ignores case if the variable case-fold-search is non-nil.

(char-to-string c)

Create a one-character string containing c.

Strings

A string is a sequence of characters, and is written by enclosing the characters in double-quotes, "like this". If a double-quote or backslash ...