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10.2.7 Special Forms

A special form is a primitive specially marked so that its arguments are not all evaluated. Most special forms define control structures or perform variable bindings—things which functions cannot do.

Each special form has its own rules for which arguments are evaluated and which are used without evaluation. Whether a particular argument is evaluated may depend on the results of evaluating other arguments.

If an expression’s first symbol is that of a special form, the expression should follow the rules of that special form; otherwise, Emacs’s behavior is not well-defined (though it will not crash). For example, ((lambda (x) x . 3) 4) contains a subexpression that begins with lambda but is not a well-formed lambda expression, so Emacs may signal an error, or may return 3 or 4 or nil, or may behave in other ways.

Function: special-form-p object ¶

This predicate tests whether its argument is a special form, and returns t if so, nil otherwise.

Here is a list, in alphabetical order, of all of the special forms in Emacs Lisp with a reference to where each is described.

and

see Constructs for Combining Conditions

catch

see Explicit Nonlocal Exits: catch and throw

cond

see Conditionals

condition-case

see Writing Code to Handle Errors

defconst

see Defining Global Variables

defvar

see Defining Global Variables

function

see Anonymous Functions

if

see Conditionals

interactive

see Interactive Call

lambda

see Lambda Expressions

let

let*

see Local Variables

or

see Constructs for Combining Conditions

prog1

prog2

progn

see Sequencing

quote

see Quoting

save-current-buffer

see The Current Buffer

save-excursion

see Excursions

save-restriction

see Narrowing

setq

see Setting Variable Values

setq-default

see Creating and Deleting Buffer-Local Bindings

unwind-protect

see Nonlocal Exits

while

see Iteration

Common Lisp note: Here are some comparisons of special forms in GNU Emacs Lisp and Common Lisp. setq, if, and catch are special forms in both Emacs Lisp and Common Lisp. save-excursion is a special form in Emacs Lisp, but doesn’t exist in Common Lisp. throw is a special form in Common Lisp (because it must be able to throw multiple values), but it is a function in Emacs Lisp (which doesn’t have multiple values).