@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990-1994, 1998, 2001-2012 Free Software Foundation, Inc.
+@c Copyright (C) 1990-1994, 1998, 2001-2013 Free Software Foundation,
+@c Inc.
@c See the file elisp.texi for copying conditions.
-@setfilename ../../info/eval
-@node Evaluation, Control Structures, Symbols, Top
+@node Evaluation
@chapter Evaluation
@cindex evaluation
@cindex interpreter
@cindex form
@cindex expression
@cindex S-expression
+@cindex sexp
A Lisp object that is intended for evaluation is called a @dfn{form}
or @dfn{expression}@footnote{It is sometimes also referred to as an
@dfn{S-expression} or @dfn{sexp}, but we generally do not use this
@dfn{form} (or an @dfn{expression}). How Emacs evaluates a form
depends on its data type. Emacs has three different kinds of form
that are evaluated differently: symbols, lists, and ``all other
-types.'' This section describes all three kinds, one by one, starting
+types''. This section describes all three kinds, one by one, starting
with the ``all other types'' which are self-evaluating forms.
@menu
into the function cell of @code{first}, and the symbol @code{first} into
the function cell of @code{erste}.
-@smallexample
+@example
@group
;; @r{Build this function cell linkage:}
;; ------------- ----- ------- -------
;; | #<subr car> | <-- | car | <-- | first | <-- | erste |
;; ------------- ----- ------- -------
@end group
-@end smallexample
-
-@smallexample
@group
(symbol-function 'car)
@result{} #<subr car>
(erste '(1 2 3)) ; @r{Call the function referenced by @code{erste}.}
@result{} 1
@end group
-@end smallexample
+@end example
By contrast, the following example calls a function without any symbol
function indirection, because the first element is an anonymous Lisp
function, not a symbol.
-@smallexample
+@example
@group
((lambda (arg) (erste arg))
'(1 2 3))
@result{} 1
@end group
-@end smallexample
+@end example
@noindent
Executing the function itself evaluates its body; this does involve
symbol function indirection when calling @code{erste}.
+ This form is rarely used and is now deprecated. Instead, you should write it
+as:
+
+@example
+@group
+(funcall (lambda (arg) (erste arg))
+ '(1 2 3))
+@end group
+@end example
+or just
+@example
+@group
+(let ((arg '(1 2 3))) (erste arg))
+@end group
+@end example
+
The built-in function @code{indirect-function} provides an easy way to
perform symbol function indirection explicitly.
Here is how you could define @code{indirect-function} in Lisp:
-@smallexample
+@example
(defun indirect-function (function)
(if (symbolp function)
(indirect-function (symbol-function function))
function))
-@end smallexample
+@end example
@end defun
@node Function Forms
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, @code{((lambda (x) x . 3) 4)} contains a subexpression that
+begins with @code{lambda} but is not a well-formed @code{lambda}
+expression, so Emacs may signal an error, or may return 3 or 4 or
+@code{nil}, or may behave in other ways.
+
Here is a list, in alphabetical order, of all of the special forms in
Emacs Lisp with a reference to where each is described.
@item defconst
@pxref{Defining Variables}
-@item defmacro
-@pxref{Defining Macros}
-
-@item defun
-@pxref{Defining Functions}
-
@item defvar
@pxref{Defining Variables}
@item interactive
@pxref{Interactive Call}
+@item lambda
+@pxref{Lambda Expressions}
+
@item let
@itemx let*
@pxref{Local Variables}
@item save-restriction
@pxref{Narrowing}
-@item save-window-excursion
-@pxref{Window Configurations}
-
@item setq
@pxref{Setting Variables}
@item while
@pxref{Iteration}
-
-@item with-output-to-temp-buffer
-@pxref{Temporary Displays}
@end table
@cindex CL note---special forms compared
@b{Common Lisp note:} Here are some comparisons of special forms in
GNU Emacs Lisp and Common Lisp. @code{setq}, @code{if}, and
@code{catch} are special forms in both Emacs Lisp and Common Lisp.
-@code{defun} is a special form in Emacs Lisp, but a macro in Common
-Lisp. @code{save-excursion} is a special form in Emacs Lisp, but
+@code{save-excursion} is a special form in Emacs Lisp, but
doesn't exist in Common Lisp. @code{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).@refill
+values).
@end quotation
@node Autoloading
expressions that were read, evaluated, and printed from buffers
(including the minibuffer) by the standard Emacs commands which do
this. (Note that this does @emph{not} include evaluation in
-@samp{*ielm*} buffers, nor evaluation using @kbd{C-j} in
+@file{*ielm*} buffers, nor evaluation using @kbd{C-j} in
@code{lisp-interaction-mode}.) The elements are ordered most recent
first.
HCoop / bpt / emacs.git / blobdiff