From: Matthew Kerwin <matthew@...>
Date: 2013-01-08T13:34:12+09:00
Subject: Re: How to identify whether a line of code will return?

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On 8 January 2013 14:09, Josh Cheek <josh.cheek@gmail.com> wrote:

> Thought maybe I could solve it with regexes, but I've come to the
> conclusion that I don't understand the return keyword at all :/
>
> I can't explain cases like this, for example:
>
> $ echo '-> { a = (return && 1) }' | ruby -c
> -:1: void value expression
> -> { a = (return && 1) }
>                       ^
>
> $ echo '-> { a = (1 && return) }' | ruby -c
> Syntax OK
>

I agree, it's pretty weird.  I would guess the "void value expression"
error is actually the parser complaining that the left hand operand of
(({&&}}) is void.  The right hand side is allowed to be void so we can do
things like (({foo.bad? && asplode})).  Odd that it doesn't mind the right
hand side of the assignment operator being void; I guess the parser can't
determine, and by the time it's evaluated at runtime, the (({return})) has
already executed, so the point is moot.

By the way, if you do manage to solve the halting problem, please let us
all know.

Cheers!
-- 
  Matthew Kerwin, B.Sc (CompSci) (Hons)
  http://matthew.kerwin.net.au/
  ABN: 59-013-727-651

  "You'll never find a programming language that frees
  you from the burden of clarifying your ideas." - xkcd

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<div dir=3D"ltr">On 8 January 2013 14:09, Josh Cheek <span dir=3D"ltr">&lt;=
<a href=3D"mailto:josh.cheek@gmail.com" target=3D"_blank">josh.cheek@gmail.=
com</a>&gt;</span> wrote:<div class=3D"gmail_extra"><div class=3D"gmail_quo=
te"><blockquote class=3D"gmail_quote" style=3D"margin:0px 0px 0px 0.8ex;bor=
der-left-width:1px;border-left-color:rgb(204,204,204);border-left-style:sol=
id;padding-left:1ex">
<div>Thought maybe I could solve it with regexes, but I&#39;ve come to the =
conclusion that I don&#39;t understand the return keyword at all :/</div><d=
iv><br></div><div>I can&#39;t explain cases like this, for example:</div>

<div><div><br></div><div><div>$ echo &#39;-&gt; { a =3D (return &amp;&amp; =
1) }&#39; | ruby -c</div><div class=3D"im"><div>-:1: void value expression<=
/div></div><div>-&gt; { a =3D (return &amp;&amp; 1) }</div><div>=A0 =A0 =A0=
 =A0 =A0 =A0 =A0 =A0 =A0 =A0 =A0 ^</div>
<div><br>
</div><div>$ echo &#39;-&gt; { a =3D (1 &amp;&amp; return) }&#39; | ruby -c=
</div><div>Syntax OK</div></div></div>
</blockquote></div><br>I agree, it&#39;s pretty weird. =A0I would guess the=
 &quot;void value expression&quot; error is actually the parser complaining=
 that the left hand operand of (({&amp;&amp;}}) is void. =A0The right hand =
side is allowed to be void so we can do things like (({foo.bad? &amp;&amp; =
asplode})). =A0Odd that it doesn&#39;t mind the right hand side of the assi=
gnment operator being void; I guess the parser can&#39;t determine, and by =
the time it&#39;s evaluated at runtime, the (({return})) has already execut=
ed, so the point is moot.</div>
<div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">By the way,=
 if you do manage to solve the halting problem, please let us all know.</di=
v><div class=3D"gmail_extra"><br></div><div class=3D"gmail_extra">Cheers!</=
div>
<div class=3D"gmail_extra">-- <br>=A0 Matthew Kerwin, B.Sc (CompSci) (Hons)=
<br>=A0 <a href=3D"http://matthew.kerwin.net.au/" target=3D"_blank">http://=
matthew.kerwin.net.au/</a><br>=A0 ABN: 59-013-727-651<br><br>=A0 &quot;You&=
#39;ll never find a programming language that frees<br>
=A0 you from the burden of clarifying your ideas.&quot; - xkcd
</div></div>

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