@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
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
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
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}.
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
@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,
@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
projects / emacs.git / commitdiff