* Re: master 12f63c18f6 1/2: Add new macro 'while-let' [not found] ` <20220928112814.B0924C12D9B@vcs2.savannah.gnu.org> @ 2022-09-28 15:25 ` Philip Kaludercic 2022-09-29 10:29 ` Lars Ingebrigtsen 0 siblings, 1 reply; 10+ messages in thread From: Philip Kaludercic @ 2022-09-28 15:25 UTC (permalink / raw) To: emacs-devel; +Cc: Lars Ingebrigtsen Lars Ingebrigtsen <larsi@gnus.org> writes: > branch: master > commit 12f63c18f6d5a886f62f10b4c8de8de3509e52df > Author: Lars Ingebrigtsen <larsi@gnus.org> > Commit: Lars Ingebrigtsen <larsi@gnus.org> > > Add new macro 'while-let' > > * doc/lispref/control.texi (Conditionals): Document > when-let/if-let/while-let. > * lisp/subr.el (while-let): New macro. > --- > doc/lispref/control.texi | 42 ++++++++++++++++++++++++++++++++++++++++++ > etc/NEWS | 4 ++++ > lisp/subr.el | 13 +++++++++++++ > 3 files changed, 59 insertions(+) > > diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi > index ee2acdb002..9635b335bc 100644 > --- a/doc/lispref/control.texi > +++ b/doc/lispref/control.texi > @@ -294,6 +294,48 @@ For example: > @end group > @end example > > +If can be convenient to bind variables in conjunction with using a > +conditional. It's often the case that you do a computation, and then > +want to do something with that computation if it's non-@code{nil}. > +The straightforward way to do that is to just write, for instance: > + > +@example > +(let ((result1 (do-computation))) > + (when result1 > + (let ((result2 (do-more result1))) > + (when result2 > + (do-something result2))))) > +@end example > + > +Since this is a very common pattern, Emacs provides a number of macros > +to make this easier and more readable. The above can be written the > +following way instead: > + > +@example > +(when-let ((result1 (do-computation)) > + (result2 (do-more result1))) > + (do-something result2)) > +@end example > + > +There's a number of variations on this theme, and they're briefly > +described below. > + > +@defmac if-let spec then-form else-forms... > +Evaluate each binding in @var{spec} in turn, like in @code{let*} > +(@pxref{Local Variables}, stopping if a binding value is @code{nil}. > +If all are non-@code{nil}, return the value of @var{then-form}, > +otherwise the last form in @var{else-forms}. > +@end defmac > + > +@defmac when-let spec then-forms... > +Like @code{if-let}, but without @var{else-forms}. > +@end defmac > + > +@defmac while-let spec then-forms... > +Like @code{when-let}, but repeat until a binding in @var{spec} is > +@code{nil}. The return value is always @code{nil}. > +@end defmac > + > @node Combining Conditions > @section Constructs for Combining Conditions > @cindex combining conditions > diff --git a/etc/NEWS b/etc/NEWS > index b85975944a..e70f9be546 100644 > --- a/etc/NEWS > +++ b/etc/NEWS > @@ -3012,6 +3012,10 @@ The following generalized variables have been made obsolete: > \f > * Lisp Changes in Emacs 29.1 > > ++++ > +** New macro 'while-let'. > +This is like 'when-let', but repeats until a binding form is nil. > + > +++ > ** New function 'make-obsolete-generalized-variable'. > This can be used to mark setters used by 'setf' as obsolete, and the > diff --git a/lisp/subr.el b/lisp/subr.el > index 26fba4771b..2a8fc46a9f 100644 > --- a/lisp/subr.el > +++ b/lisp/subr.el > @@ -2514,7 +2514,20 @@ The variable list SPEC is the same as in `if-let'." > (declare (indent 1) (debug if-let)) > (list 'if-let spec (macroexp-progn body))) > > +(defmacro while-let (spec &rest body) > + "Bind variables according to SPEC and conditionally evaluate BODY. > +Evaluate each binding in turn, stopping if a binding value is nil. > +If all bindings are non-nil, eval BODY and repeat. > > +The variable list SPEC is the same as in `if-let'." > + (declare (indent 1) (debug if-let)) > + (let ((done (gensym "done"))) > + `(catch ',done > + (while t > + (if-let ,spec Is `if-let' used intentionally here, or would if-let* be better? > + (progn > + ,@body) > + (throw ',done nil)))))) > > ;; PUBLIC: find if the current mode derives from another. > ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-09-28 15:25 ` master 12f63c18f6 1/2: Add new macro 'while-let' Philip Kaludercic @ 2022-09-29 10:29 ` Lars Ingebrigtsen 2022-09-29 11:42 ` Philip Kaludercic 0 siblings, 1 reply; 10+ messages in thread From: Lars Ingebrigtsen @ 2022-09-29 10:29 UTC (permalink / raw) To: Philip Kaludercic; +Cc: emacs-devel Philip Kaludercic <philipk@posteo.net> writes: > Is `if-let' used intentionally here, or would if-let* be better? The latter. Now fixed. ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-09-29 10:29 ` Lars Ingebrigtsen @ 2022-09-29 11:42 ` Philip Kaludercic 2022-09-29 11:48 ` Lars Ingebrigtsen 0 siblings, 1 reply; 10+ messages in thread From: Philip Kaludercic @ 2022-09-29 11:42 UTC (permalink / raw) To: Lars Ingebrigtsen; +Cc: emacs-devel Lars Ingebrigtsen <larsi@gnus.org> writes: > Philip Kaludercic <philipk@posteo.net> writes: > >> Is `if-let' used intentionally here, or would if-let* be better? > > The latter. Now fixed. In that case ought the macro not be called `while-let*'? ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-09-29 11:42 ` Philip Kaludercic @ 2022-09-29 11:48 ` Lars Ingebrigtsen 2022-10-15 14:12 ` Philip Kaludercic 0 siblings, 1 reply; 10+ messages in thread From: Lars Ingebrigtsen @ 2022-09-29 11:48 UTC (permalink / raw) To: Philip Kaludercic; +Cc: emacs-devel Philip Kaludercic <philipk@posteo.net> writes: > In that case ought the macro not be called `while-let*'? Nope. We're pretending that the * versions of these macros don't exist (by not mentioning them in the manual), and we're likewise pretending that if-let doesn't have wider semantics than the * version (by not mentioning that, either). ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-09-29 11:48 ` Lars Ingebrigtsen @ 2022-10-15 14:12 ` Philip Kaludercic 2022-10-16 7:45 ` Lars Ingebrigtsen 0 siblings, 1 reply; 10+ messages in thread From: Philip Kaludercic @ 2022-10-15 14:12 UTC (permalink / raw) To: Lars Ingebrigtsen; +Cc: emacs-devel Lars Ingebrigtsen <larsi@gnus.org> writes: > Philip Kaludercic <philipk@posteo.net> writes: > >> In that case ought the macro not be called `while-let*'? > > Nope. We're pretending that the * versions of these macros don't exist > (by not mentioning them in the manual), and we're likewise pretending > that if-let doesn't have wider semantics than the * version (by not > mentioning that, either). On that topic, why do we have `and-let*' and no `and-let'? ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-10-15 14:12 ` Philip Kaludercic @ 2022-10-16 7:45 ` Lars Ingebrigtsen 2022-10-16 9:26 ` Philip Kaludercic 0 siblings, 1 reply; 10+ messages in thread From: Lars Ingebrigtsen @ 2022-10-16 7:45 UTC (permalink / raw) To: Philip Kaludercic; +Cc: emacs-devel Philip Kaludercic <philipk@posteo.net> writes: > On that topic, why do we have `and-let*' and no `and-let'? I'd rather ask "why do we have and-let at all"? 😀 If you look at the in-tree usages of and-let*, most of them should clearly have been when-let instead, so I think it was a mistake to add and-let. ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-10-16 7:45 ` Lars Ingebrigtsen @ 2022-10-16 9:26 ` Philip Kaludercic 2022-10-16 22:59 ` Sean Whitton 0 siblings, 1 reply; 10+ messages in thread From: Philip Kaludercic @ 2022-10-16 9:26 UTC (permalink / raw) To: Lars Ingebrigtsen; +Cc: emacs-devel Lars Ingebrigtsen <larsi@gnus.org> writes: > Philip Kaludercic <philipk@posteo.net> writes: > >> On that topic, why do we have `and-let*' and no `and-let'? > > I'd rather ask "why do we have and-let at all"? 😀 > > If you look at the in-tree usages of and-let*, most of them should > clearly have been when-let instead, so I think it was a mistake to add > and-let. I have recently started appreciating `and-let*' when I want to make it explicit that the last binding is the return value, but I guess that any (and-let* ((foo bar) ... (baz qux))) is the same as (when-let ((foo bar) ...) (baz qux)) ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-10-16 9:26 ` Philip Kaludercic @ 2022-10-16 22:59 ` Sean Whitton 2022-10-17 0:14 ` [External] : " Drew Adams 0 siblings, 1 reply; 10+ messages in thread From: Sean Whitton @ 2022-10-16 22:59 UTC (permalink / raw) To: Philip Kaludercic; +Cc: Lars Ingebrigtsen, emacs-devel Hello, On Sun 16 Oct 2022 at 09:26AM GMT, Philip Kaludercic wrote: > Lars Ingebrigtsen <larsi@gnus.org> writes: > >> Philip Kaludercic <philipk@posteo.net> writes: >> >>> On that topic, why do we have `and-let*' and no `and-let'? >> >> I'd rather ask "why do we have and-let at all"? 😀 >> >> If you look at the in-tree usages of and-let*, most of them should >> clearly have been when-let instead, so I think it was a mistake to add >> and-let. > > I have recently started appreciating `and-let*' when I want to make it > explicit that the last binding is the return value, but I guess that any > > (and-let* ((foo bar) ... (baz qux))) > > is the same as > > (when-let ((foo bar) ...) (baz qux)) Yeah, that's a Lisp convention I learned from Magit's maintainer -- when/unless for side-effects, and/or for return value. I appreciate having and-let for this reason. -- Sean Whitton ^ permalink raw reply [flat|nested] 10+ messages in thread
* RE: [External] : Re: master 12f63c18f6 1/2: Add new macro 'while-let' 2022-10-16 22:59 ` Sean Whitton @ 2022-10-17 0:14 ` Drew Adams 0 siblings, 0 replies; 10+ messages in thread From: Drew Adams @ 2022-10-17 0:14 UTC (permalink / raw) To: Sean Whitton, Philip Kaludercic; +Cc: Lars Ingebrigtsen, emacs-devel@gnu.org > Yeah, that's a Lisp convention I learned from Magit's maintainer -- > when/unless for side-effects, and/or for return value. I appreciate > having and-let for this reason. It's a very old convention (and a good one) - even called out in "Common Lisp The Language" (from the beginning). ^ permalink raw reply [flat|nested] 10+ messages in thread
* Re: master 12f63c18f6 1/2: Add new macro 'while-let' @ 2022-09-28 12:04 Visuwesh 0 siblings, 0 replies; 10+ messages in thread From: Visuwesh @ 2022-09-28 12:04 UTC (permalink / raw) To: emacs-devel; +Cc: Lars Ingebrigtsen >branch: master >commit 12f63c18f6d5a886f62f10b4c8de8de3509e52df >Author: Lars Ingebrigtsen <larsi@gnus.org> >Commit: Lars Ingebrigtsen <larsi@gnus.org> > > Add new macro 'while-let' > > * doc/lispref/control.texi (Conditionals): Document > when-let/if-let/while-let. > * lisp/subr.el (while-let): New macro. >--- > doc/lispref/control.texi | 42 ++++++++++++++++++++++++++++++++++++++++++ > etc/NEWS | 4 ++++ > lisp/subr.el | 13 +++++++++++++ > 3 files changed, 59 insertions(+) > >diff --git a/doc/lispref/control.texi b/doc/lispref/control.texi >index ee2acdb002..9635b335bc 100644 >--- a/doc/lispref/control.texi >+++ b/doc/lispref/control.texi >@@ -294,6 +294,48 @@ For example: > @end group > @end example > >+If can be convenient to bind variables in conjunction with using a ^^ Typo: this should be "It". >+conditional. It's often the case that you do a computation, and then >+want to do something with that computation if it's non-@code{nil}. >+The straightforward way to do that is to just write, for instance: ^ permalink raw reply [flat|nested] 10+ messages in thread
end of thread, other threads:[~2022-10-17 0:14 UTC | newest] Thread overview: 10+ messages (download: mbox.gz / follow: Atom feed) -- links below jump to the message on this page -- [not found] <166436449368.11560.17915607619196292155@vcs2.savannah.gnu.org> [not found] ` <20220928112814.B0924C12D9B@vcs2.savannah.gnu.org> 2022-09-28 15:25 ` master 12f63c18f6 1/2: Add new macro 'while-let' Philip Kaludercic 2022-09-29 10:29 ` Lars Ingebrigtsen 2022-09-29 11:42 ` Philip Kaludercic 2022-09-29 11:48 ` Lars Ingebrigtsen 2022-10-15 14:12 ` Philip Kaludercic 2022-10-16 7:45 ` Lars Ingebrigtsen 2022-10-16 9:26 ` Philip Kaludercic 2022-10-16 22:59 ` Sean Whitton 2022-10-17 0:14 ` [External] : " Drew Adams 2022-09-28 12:04 Visuwesh
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