From: Richard Copley <rcopley@gmail.com>
To: Noam Postavsky <npostavs@users.sourceforge.net>
Cc: Rolf Ade <rolf@pointsman.de>, Emacs developers <emacs-devel@gnu.org>
Subject: Re: Anaphoric macros: increase visibility
Date: Sat, 14 Jan 2017 04:13:20 +0000 [thread overview]
Message-ID: <CAPM58oi9AUc9LshrmQKoz06MLCWw3rsZqJrSdOO=0LwS96JvHg@mail.gmail.com> (raw)
In-Reply-To: <CAM-tV-9SFZoYvy=kcM_VPLoUomfLdgDL5bf14ymTcYuGEEo_4A@mail.gmail.com>
On 14 January 2017 at 03:03, Noam Postavsky
<npostavs@users.sourceforge.net> wrote:
> On Fri, Jan 13, 2017 at 9:30 PM, Rolf Ade <rolf@pointsman.de> wrote:
>>
>> Michael Heerdegen <michael_heerdegen@web.de> writes:
>>> We also already have `if-let' and `when-let' in "subr-x". They are like
>>> `aif' and `awhen' but you specify "it" explicitly.
>>
>> Since you mention them ... I probably miss something obvious but from
>> looking at the documentation of if-let
>>
>> (if-let BINDINGS THEN &rest ELSE)
>>
>> and of when-let
>>
>> (when-let BINDINGS &rest BODY)
>>
>> I don't get, why there is a need for when-let?
>>
>
> Just like there is both `if' and `when', it's useful to have both
> `if-let' and `when-let'.
>
Rolf, `when' and `when-let' are macros that expand to the corresponding
`if' form without an ELSE, so strictly the `when' forms are redundant,
as you suggest. But they make the code easier and quicker to read
(and feel a little more natural to write), because you know the ELSE
is null without having to think about it. Finding the ELSE (if any) of
an `if' form can be quite a pain. The unusual indentation of the THEN
clause exists for the same reason, but it's a bit ugly, which is a
second (maybe less important) motivation for `when'.
next prev parent reply other threads:[~2017-01-14 4:13 UTC|newest]
Thread overview: 20+ messages / expand[flat|nested] mbox.gz Atom feed top
2017-01-13 8:39 Anaphoric macros: increase visibility Tino Calancha
2017-01-13 19:48 ` Michael Heerdegen
2017-01-14 2:30 ` Rolf Ade
2017-01-14 2:48 ` Rolf Ade
2017-01-14 3:03 ` Noam Postavsky
2017-01-14 4:13 ` Richard Copley [this message]
2017-01-14 5:27 ` Tino Calancha
2017-01-15 0:39 ` Michael Heerdegen
2017-01-15 2:24 ` On the naming/behavior of {if, when}-let (was Re: Anaphoric macros: increase visibility) Mark Oteiza
2017-01-15 2:26 ` Anaphoric macros: increase visibility Michael Heerdegen
2017-01-15 10:24 ` Tino Calancha
2017-01-15 15:32 ` Stefan Monnier
2017-01-16 2:44 ` Tino Calancha
2017-01-16 3:59 ` Stefan Monnier
2017-01-14 6:25 ` Dmitri Paduchikh
2017-01-14 7:56 ` Tino Calancha
2017-01-14 10:15 ` Dmitri Paduchikh
2017-01-15 0:29 ` Michael Heerdegen
2017-01-15 2:03 ` Dmitri Paduchikh
2017-01-15 2:16 ` Michael Heerdegen
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