@c -*-texinfo-*-
@c This is part of the GNU Emacs Lisp Reference Manual.
-@c Copyright (C) 1990-1995, 1998-1999, 2001-2013 Free Software
+@c Copyright (C) 1990-1995, 1998-1999, 2001-2014 Free Software
@c Foundation, Inc.
@c See the file elisp.texi for copying conditions.
@node Control Structures
was returned by @code{(get-return-code x)}.
To give a more complex example, a simple interpreter for a little
-expression language could look like:
+expression language could look like (note that this example requires
+lexical binding):
@example
(defun evaluate (exp env)
(evaluate '(add 1 2) nil) ;=> 3
(evaluate '(add x y) '((x . 1) (y . 2))) ;=> 3
(evaluate '(call (fn x (add 1 x)) 2) nil) ;=> 3
-(evaluate '(sub 1 2) nil) ;=> (error "Unknown expression (sub 1 2)")
+(evaluate '(sub 1 2) nil) ;=> error
@end example
-Note that (parts of) @code{pcase} only work as expected with lexical
-binding, so lisp files using @code{pcase} should have enable it
-(@pxref{Using Lexical Binding}, for how to enable lexical binding).
-
There are two kinds of patterns involved in @code{pcase}, called
@emph{U-patterns} and @emph{Q-patterns}. The @var{upattern} mentioned above
are U-patterns and can take the following forms:
@end example
@end defmac
-@defmac with-demoted-errors body@dots{}
+@defmac with-demoted-errors format body@dots{}
This macro is like a milder version of @code{ignore-errors}. Rather
than suppressing errors altogether, it converts them into messages.
-Use this form around code that is not expected to signal errors, but
+It uses the string @var{format} to format the message.
+@var{format} should contain a single @samp{%}-sequence; e.g.,
+@code{"Error: %S"}. Use @code{with-demoted-errors} around code
+that is not expected to signal errors, but
should be robust if one does occur. Note that this macro uses
@code{condition-case-unless-debug} rather than @code{condition-case}.
@end defmac