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From: Bozhidar Batsov <bozhidar.batsov@gmail.com>
Newsgroups: gmane.emacs.devel
Subject: Re: if-let and when-let: parallel or sequential
Date: Mon, 11 Aug 2014 20:49:29 +0300
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Cc: John Mastro <john.b.mastro@gmail.com>, emacs-devel@gnu.org
To: Stefan Monnier <monnier@iro.umontreal.ca>
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On August 11, 2014 at 17:42:20, Stefan Monnier (monnier=40iro.umontreal.c=
a) wrote:
> if-let and when-let don=E2=80=99t make much sense with more than one bi=
nding=C2=A0
> form.=C2=A0

Why do you think so=3F If they only work for a single binding, the=C2=A0
benefit is really minor. It's only when you use several bindings that=C2=A0=

the benefit becomes more significant (the alternative being either=C2=A0
a very deeply nested code, or separating the var's declarations from=C2=A0=

their initialization).=C2=A0


Stefan=C2=A0
Practically speaking, the most common case people run into is checking wh=
ether a single object is nil=C2=A0

and binding it to some local if it=E2=80=99s not. Binding multiple locals=
 in such a form reduces the clarity of the code because the=C2=A0

semantics are not that clear anymore - should all the forms produce non-n=
il or should only the first form produce non-nil=3F Obviously=C2=A0

people can (and should) read the documentation, but I=E2=80=99m a huge be=
liever in intuitive APIs. That said, I=E2=80=99m fine with whatever=C2=A0=


behavior you decide upon, as I believe those functions are valuable addit=
ions regardless.


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<html><head><style>body=7Bfont-family:Helvetica,Arial;font-size:13px=7D</=
style></head><body style=3D=22word-wrap: break-word; -webkit-nbsp-mode: s=
pace; -webkit-line-break: after-white-space;=22><div id=3D=22bloop=5Fcust=
omfont=22 style=3D=22font-family:Helvetica,Arial;font-size:13px; color: r=
gba(0,0,0,1.0); margin: 0px; line-height: auto;=22>On August 11, 2014 at =
17:42:20, Stefan Monnier (<a href=3D=22mailto:monnier=40iro.umontreal.ca=22=
>monnier=40iro.umontreal.ca</a>) wrote:</div> <div><div><blockquote type=3D=
=22cite=22 class=3D=22clean=5Fbq=22 style=3D=22color: rgb(0, 0, 0); font-=
family: Helvetica, Arial; font-size: 13px; font-style: normal; font-varia=
nt: normal; font-weight: normal; letter-spacing: normal; line-height: nor=
mal; orphans: auto; text-align: start; text-indent: 0px; text-transform: =
none; white-space: normal; widows: auto; word-spacing: 0px; -webkit-text-=
stroke-width: 0px; background-color: rgb(255, 255, 255);=22><span><div><d=
iv></div><div>&gt; if-let and when-let don=E2=80=99t make much sense with=
 more than one binding<span class=3D=22Apple-converted-space=22>&nbsp;</s=
pan><br>&gt; form.<span class=3D=22Apple-converted-space=22>&nbsp;</span>=
<br><br>Why do you think so=3F If they only work for a single binding, th=
e<span class=3D=22Apple-converted-space=22>&nbsp;</span><br>benefit is re=
ally minor. It's only when you use several bindings that<span class=3D=22=
Apple-converted-space=22>&nbsp;</span><br>the benefit becomes more signif=
icant (the alternative being either<span class=3D=22Apple-converted-space=
=22>&nbsp;</span><br>a very deeply nested code, or separating the var's d=
eclarations from<span class=3D=22Apple-converted-space=22>&nbsp;</span><b=
r>their initialization).<span class=3D=22Apple-converted-space=22>&nbsp;<=
/span><br><br><br>Stefan<span class=3D=22Apple-converted-space=22>&nbsp;<=
/span></div></div></span></blockquote></div><p>Practically speaking, the =
most common case people run into is checking whether a single object is n=
il&nbsp;</p><p>and binding it to some local if it=E2=80=99s not. Binding =
multiple locals in such a form reduces the clarity of the code because th=
e&nbsp;</p><p>semantics are not that clear anymore - should all the forms=
 produce non-nil or should only the first form produce non-nil=3F Obvious=
ly&nbsp;</p><p>people can (and should) read the documentation, but I=E2=80=
=99m a huge believer in intuitive APIs. That said, I=E2=80=99m fine with =
whatever&nbsp;</p><p>behavior you decide upon, as I believe those functio=
ns are valuable additions regardless.</p><div></div></div></body></html>
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