Special Forms

A special form is a primitive function 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 Combining Conditions
catch: see Catch and Throw
cond: see Conditionals
condition-case: see Handling Errors
defconst: see Defining Variables
defvar: see Defining Variables
function: see Anonymous Functions
if: see Conditionals
interactive: see Interactive Call
lambda: see Lambda Expressions
let
let*: see Local Variables
or: see Combining Conditions
prog1
prog2
progn: see Sequencing
quote: see Quoting
save-current-buffer: see Current Buffer
save-excursion: see Excursions
save-restriction: see Narrowing
setq: see Setting Variables
setq-default: see Creating Buffer-Local
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).