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[bpt/emacs.git] / doc / lispref / control.texi

diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi
index 34a02aa..edf60dd 100644 (file)
--- a/doc/lispref/control.texi
+++ b/doc/lispref/control.texi
@@ -1,6 +1,6 @@
 @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
@@ -322,13 +322,14 @@ In the last clause, @code{code} is a variable that gets bound to the value that
 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)
   (pcase exp
     (`(add ,x ,y)         (+ (evaluate x env) (evaluate y env)))
-    (`(call ,fun ,arg)    (funcall (evaluate fun) (evaluate arg env)))
+    (`(call ,fun ,arg)    (funcall (evaluate fun env) (evaluate arg env)))
     (`(fn ,arg ,body)     (lambda (val)
                             (evaluate body (cons (cons arg val) env))))
     ((pred numberp)       exp)
@@ -342,6 +343,15 @@ third elements and binds them to the variables @code{x} and @code{y}.
 @code{(pred numberp)} is a pattern that simply checks that @code{exp}
 is a number, and @code{_} is the catch-all pattern that matches anything.
 
+Here are some sample programs including their evaluation results:
+
+@example
+(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
+@end example
+
 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:
@@ -1242,10 +1252,13 @@ Here's the example at the beginning of this subsection rewritten using
 @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