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<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Well, both versions have their pros and
cons. Probably depending on the number of variables, it might be better to use the
“side effect” of the case clause as it shortens the code
significantly.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>What I am more worried about is the effect
it has on the automatic source code processing like refactoring, parse
transforms, etc. For instance if we have<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Value = case Var of <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> one->Tmp=blah_blah,
calcValue(SomeArgs);<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> two->Tmp=blah_2,
calcValue(OtherArgs);<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>end,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>… code goes on …<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>do_something(Tmp, YetOtherArgs)..<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Later one decides to extract a function (aka
extract a method in OO), then the code should be rewritten as<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>{Value, Tmp} = new_func(…);<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>….<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>new_func(..) -><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>Value = case Var of <o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> one->Tmp=blah_blah,
calcValue(SomeArgs);<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'> two->Tmp=blah_2,
calcValue(OtherArgs);<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>end,<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>{Value, Tmp}.<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>So the question is: are these kind of
features easily handled in the AST? Do refactoring tools have to take special
care of the case like that?<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'>P.S. All these questions arose only because
the binary match specs have to be static, not like:<o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><<A:1/unit:32-Endianness,
Rest>> = Binary. </span></font><font size=2 color=navy face=Wingdings><span
style='font-size:10.0pt;font-family:Wingdings;color:navy'>J</span></font><font
size=2 color=navy face=Arial><span style='font-size:10.0pt;font-family:Arial;
color:navy'><o:p></o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=2 color=navy face=Arial><span style='font-size:
10.0pt;font-family:Arial;color:navy'><o:p> </o:p></span></font></p>
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face="Times New Roman"><span style='font-size:12.0pt'>
<hr size=2 width="100%" align=center tabindex=-1>
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<p class=MsoNormal><b><font size=2 face=Tahoma><span style='font-size:10.0pt;
font-family:Tahoma;font-weight:bold'>From:</span></font></b><font size=2
face=Tahoma><span style='font-size:10.0pt;font-family:Tahoma'>
erlang-questions-bounces@erlang.org
[mailto:erlang-questions-bounces@erlang.org] <b><span style='font-weight:bold'>On
Behalf Of </span></b>Robert Virding<br>
<b><span style='font-weight:bold'>Sent:</span></b> 10. maaliskuuta 2008 23:14<br>
<b><span style='font-weight:bold'>To:</span></b> Jay Nelson<br>
<b><span style='font-weight:bold'>Cc:</span></b> erlang-questions@erlang.org<br>
<b><span style='font-weight:bold'>Subject:</span></b> Re: [erlang-questions]
(no subject)</span></font><o:p></o:p></p>
</div>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'><o:p> </o:p></span></font></p>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>On 10/03/2008, <b><span style='font-weight:bold'>Jay Nelson</span></b>
<<a href="mailto:jay@duomark.com">jay@duomark.com</a>> wrote:<o:p></o:p></span></font></p>
<div>
<blockquote style='border:none;border-left:solid #CCCCCC 1.0pt;padding:0in 0in 0in 6.0pt;
margin-left:4.8pt;margin-right:0in'>
<p class=MsoNormal><font size=3 face="Times New Roman"><span style='font-size:
12.0pt'>I stand corrected. I wasn't aware of the compiler error
because I<br>
avoid that style of code.<br>
<br>
The reason I avoid it, is that I find it more difficult to visually<br>
verify in the editor. Also, if more clauses are added in the future,<br>
you have to keep track that the following code relies on setting some<br>
variables (or else, apparently, wait until you compile to notice you<br>
need some others).<br>
<br>
I just find that the following style:<br>
<br>
{ ... args needed ... } = compound statement,<br>
use args<br>
<br>
advertises the programmer's intent much more clearly. It states that<br>
the compound statement is being executed for the side effect of<br>
binding a particular set of variables. This binding environment is<br>
necessary for the following statements. It corresponds to a (let<br>
(...) ...) clause in lisp.<o:p></o:p></span></font></p>
</blockquote>
<div>
<p class=MsoNormal style='margin-bottom:12.0pt'><font size=3
face="Times New Roman"><span style='font-size:12.0pt'><br>
Yes, it is a matter of style which method you use. The scope of variables is
the whole function clause. I also prefer returning the values which are
"exported" from the if/case/receive, it is clearer, but I am not
always consistent in this I know. Although many prefer just exporting them.
Unfortunately it is impossible to be completely consistent all the time as the
compiler quite happily exports all variables which are bound in all clauses.
This can cause some confusion. So if you have:<br>
<br>
case ... of<br>
... -> ..., Tmp = ..., ...;<br>
... -> ..., Tmp = ..., ...;<br>
...<br>
end,<br>
<br>
where Tmp is bound in all clauses then Tmp will automatically be exported. And
if it is then later used it will already be bound, which can cause some
confusion. So you have to be certain to use unique names for temporary
variables. This is another reason to avoid large function clauses where it can
be harder to see reuse.<br>
<br>
There is no way around this.<br>
<br>
Robert<o:p></o:p></span></font></p>
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