From 4ddedf94c8529de0c13b74c1156d89872f94c155 Mon Sep 17 00:00:00 2001
From: Glenn Morris <rgm@gnu.org>
Date: Tue, 30 Oct 2012 00:34:37 -0700
Subject: [PATCH] Doc and manual updates for cl-letf and letf Fixes:
debbugs:12760
* doc/misc/cl.texi (Modify Macros): Update for cl-letf changes.
(Obsolete Lexical Macros): Say a little more about letf/cl-letf.
* lisp/emacs-lisp/cl.el (letf): Doc fix.
* etc/NEWS: Related edit.
---
doc/misc/ChangeLog | 5 ++++
doc/misc/cl.texi | 59 +++++++++++++++++++++++++++----------------
etc/NEWS | 3 +++
lisp/ChangeLog | 4 +++
lisp/emacs-lisp/cl.el | 4 ++-
5 files changed, 52 insertions(+), 23 deletions(-)
diff --git a/doc/misc/ChangeLog b/doc/misc/ChangeLog
index 92b5b243ec9..b07db9d605f 100644
--- a/doc/misc/ChangeLog
+++ b/doc/misc/ChangeLog
@@ -1,3 +1,8 @@
+2012-10-30 Glenn Morris <rgm@gnu.org>
+
+ * cl.texi (Modify Macros): Update for cl-letf changes.
+ (Obsolete Lexical Macros): Say a little more about letf/cl-letf.
+
2012-10-29 Glenn Morris <rgm@gnu.org>
* cl.texi (Organization): More details on cl-lib.el versus cl.el.
diff --git a/doc/misc/cl.texi b/doc/misc/cl.texi
index 01068d57071..f520144679e 100644
--- a/doc/misc/cl.texi
+++ b/doc/misc/cl.texi
@@ -882,7 +882,7 @@ generalized variables.
@menu
* Setf Extensions:: Additional @code{setf} places.
-* Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{letf}, @code{cl-callf}, etc.
+* Modify Macros:: @code{cl-incf}, @code{cl-rotatef}, @code{cl-letf}, @code{cl-callf}, etc.
@end menu
@node Setf Extensions
@@ -1127,7 +1127,7 @@ conveniently exchanges @var{a} and @var{b}.
The following macros were invented for this package; they have no
analogues in Common Lisp.
-@defmac letf (bindings@dots{}) forms@dots{}
+@defmac cl-letf (bindings@dots{}) forms@dots{}
This macro is analogous to @code{let}, but for generalized variables
rather than just symbols. Each @var{binding} should be of the form
@code{(@var{place} @var{value})}; the original contents of the
@@ -1140,47 +1140,59 @@ error.
For example,
@example
-(letf (((point) (point-min))
- (a 17))
- ...)
+(cl-letf (((point) (point-min))
+ (a 17))
+ ...)
@end example
@noindent
-moves ``point'' in the current buffer to the beginning of the buffer,
+moves point in the current buffer to the beginning of the buffer,
and also binds @code{a} to 17 (as if by a normal @code{let}, since
@code{a} is just a regular variable). After the body exits, @code{a}
is set back to its original value and point is moved back to its
original position.
-Note that @code{letf} on @code{(point)} is not quite like a
+Note that @code{cl-letf} on @code{(point)} is not quite like a
@code{save-excursion}, as the latter effectively saves a marker
which tracks insertions and deletions in the buffer. Actually,
-a @code{letf} of @code{(point-marker)} is much closer to this
+a @code{cl-letf} of @code{(point-marker)} is much closer to this
behavior. (@code{point} and @code{point-marker} are equivalent
as @code{setf} places; each will accept either an integer or a
marker as the stored value.)
Since generalized variables look like lists, @code{let}'s shorthand
of using @samp{foo} for @samp{(foo nil)} as a @var{binding} would
-be ambiguous in @code{letf} and is not allowed.
+be ambiguous in @code{cl-letf} and is not allowed.
However, a @var{binding} specifier may be a one-element list
@samp{(@var{place})}, which is similar to @samp{(@var{place}
@var{place})}. In other words, the @var{place} is not disturbed
-on entry to the body, and the only effect of the @code{letf} is
-to restore the original value of @var{place} afterwards. (The
-redundant access-and-store suggested by the @code{(@var{place}
+on entry to the body, and the only effect of the @code{cl-letf} is
+to restore the original value of @var{place} afterwards.
+@c I suspect this may no longer be true; either way it's
+@c implementation detail and so not essential to document.
+@ignore
+(The redundant access-and-store suggested by the @code{(@var{place}
@var{place})} example does not actually occur.)
+@end ignore
-In most cases, the @var{place} must have a well-defined value on
-entry to the @code{letf} form. The only exceptions are plain
-variables and calls to @code{symbol-value} and @code{symbol-function}.
-If the symbol is not bound on entry, it is simply made unbound by
-@code{makunbound} or @code{fmakunbound} on exit.
+Note that in this case, and in fact almost every case, @var{place}
+must have a well-defined value outside the @code{cl-letf} body.
+There is essentially only one exception to this, which is @var{place}
+a plain variable with a specified @var{value} (such as @code{(a 17)}
+in the above example).
+@c See http://debbugs.gnu.org/12758
+@c Some or all of this was true for cl.el, but not for cl-lib.el.
+@ignore
+The only exceptions are plain variables and calls to
+@code{symbol-value} and @code{symbol-function}. If the symbol is not
+bound on entry, it is simply made unbound by @code{makunbound} or
+@code{fmakunbound} on exit.
+@end ignore
@end defmac
@defmac cl-letf* (bindings@dots{}) forms@dots{}
-This macro is to @code{letf} what @code{let*} is to @code{let}:
+This macro is to @code{cl-letf} what @code{let*} is to @code{let}:
It does the bindings in sequential rather than parallel order.
@end defmac
@@ -1210,7 +1222,7 @@ equivalent to @code{(cl-callf2 cons @var{x} @var{place})}.
The @code{cl-callf} and @code{cl-callf2} macros serve as building
blocks for other macros like @code{cl-incf}, and @code{cl-pushnew}.
-The @code{letf} and @code{cl-letf*} macros are used in the processing
+The @code{cl-letf} and @code{cl-letf*} macros are used in the processing
of symbol macros; @pxref{Macro Bindings}.
@@ -1221,7 +1233,7 @@ of symbol macros; @pxref{Macro Bindings}.
These Lisp forms make bindings to variables and function names,
analogous to Lisp's built-in @code{let} form.
-@xref{Modify Macros}, for the @code{letf} and @code{cl-letf*} forms which
+@xref{Modify Macros}, for the @code{cl-letf} and @code{cl-letf*} forms which
are also related to variable bindings.
@menu
@@ -1370,7 +1382,7 @@ I.e., @code{(setq foo 4)} in the above would be equivalent to
@code{(setf foo 4)}, which in turn expands to @code{(setf (car bar) 4)}.
Likewise, a @code{let} or @code{let*} binding a symbol macro is
-treated like a @code{letf} or @code{cl-letf*}. This differs from true
+treated like a @code{cl-letf} or @code{cl-letf*}. This differs from true
@c FIXME does it work like this in Emacs with lexical-binding = t?
Common Lisp, where the rules of lexical scoping cause a @code{let}
binding to shadow a @code{cl-symbol-macrolet} binding. In this package,
@@ -4870,7 +4882,10 @@ Replaced by @code{cl-labels} (@pxref{Function Bindings}).
@end defmac
@defmac letf (bindings@dots{}) forms@dots{}
-Replaced by @code{cl-letf} (@pxref{Modify Macros}).
+This macro is almost exactly the same as @code{cl-letf}, which
+replaces it (@pxref{Modify Macros}). The only difference is in
+details that relate to some deprecated usage of @code{symbol-function}
+in place forms.
@end defmac
@node Obsolete Setf Customization
diff --git a/etc/NEWS b/etc/NEWS
index a6d6b1c5eeb..7e8684258a6 100644
--- a/etc/NEWS
+++ b/etc/NEWS
@@ -323,7 +323,10 @@ The difference is that it relies on the `lexical-binding' machinery (as opposed
to the `lexical-let' machinery used previously) to capture definitions in
closures, so such closures will only work if `lexical-binding' is in use.
++++
*** `cl-letf' is not exactly like `letf'.
+The only difference is in details that relate to some deprecated usage
+of `symbol-function' in place forms.
+++
*** `progv' was rewritten to use the `let' machinery.
diff --git a/lisp/ChangeLog b/lisp/ChangeLog
index bd57e7dc5f0..c5c3b93d195 100644
--- a/lisp/ChangeLog
+++ b/lisp/ChangeLog
@@ -1,3 +1,7 @@
+2012-10-30 Glenn Morris <rgm@gnu.org>
+
+ * emacs-lisp/cl.el (letf): Doc fix. (Bug#12760)
+
2012-10-29 Chong Yidong <cyd@gnu.org>
* isearch.el (isearch-other-meta-char): Ensure that a reprocessed
diff --git a/lisp/emacs-lisp/cl.el b/lisp/emacs-lisp/cl.el
index 108ad037569..d3ef83961e2 100644
--- a/lisp/emacs-lisp/cl.el
+++ b/lisp/emacs-lisp/cl.el
@@ -511,7 +511,9 @@ rather than relying on `lexical-binding'."
(defmacro letf (bindings &rest body)
"Dynamically scoped let-style bindings for places.
-Like `cl-letf', but with some extra backward compatibility."
+For more details, see `cl-letf'. This macro behaves like that one
+in almost every respect (apart from details that relate to some
+deprecated usage of `symbol-function' in place forms)." ; bug#12760
(declare (indent 1) (debug cl-letf))
;; Like cl-letf, but with special handling of symbol-function.
`(cl-letf ,(mapcar (lambda (x) (if (eq (car-safe (car x)) 'symbol-function)
--
2.39.5