conditional expressions - Erlang Questions

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Message from discussion conditional expressions
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Message-ID: <3dbc6d1c0811151342j85dd4c8laead08f6c7f5c01b@mail.gmail.com>
Date: Sat, 15 Nov 2008 22:42:46 +0100
From: "Robert Virding" <rvird...@gmail.com>
To: "damien morton" <dmor...@bitfurnace.com>
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Cc: erlang-questi...@erlang.org, mats cronqvist <ma...@kreditor.se>
Subject: Re: [erlang-questions] conditional expressions
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You are evaluating these in the shell. In the first case X is bound to aaa,
which means that when you evaluate the second case X is already bound. Which
means that there is no matching clause. If you do:

1> case [] of [] -> X = aaa; X -> ok end.
aaa
2> case bbb of [] -> Y = aaa; Y -> ok end.
ok
3> {X,Y}.
{aaa,bbb}

it works.

Robert

2008/11/15 damien morton <dmor...@bitfurnace.com>

> 1> case [] of [] -> X = aaa; X -> ok end.
> aaa
> 2> case bbb of [] -> X = aaa; X -> ok end.
> ** exception error: no case clause matching bbb
>
> am I missing something?
>
> On Sun, Nov 16, 2008 at 4:42 AM, mats cronqvist <ma...@kreditor.se> wrote:
>
>>
>>   strangely, this also works;
>>
>> case foo() of
>>  [] -> X = bar();
>>  X -> ok
>> end
>>
>>  as long as X is bound in each clause, you're golden.
>>
>>  this might qualify as a gotcha.
>>
>>  mats
>>
>
>
> _______________________________________________
> erlang-questions mailing list
> erlang-questi...@erlang.org
> http://www.erlang.org/mailman/listinfo/erlang-questions
>

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You are evaluating these in the shell. In the first case X is bound to aaa, which means that when you evaluate the second case X is already bound. Which means that there is no matching clause. If you do:<br><br>1&gt; case [] of [] -&gt; X = aaa; X -&gt; ok end.<br>
aaa<br>2&gt; case bbb of [] -&gt; Y = aaa; Y -&gt; ok end.<br>ok<br>3&gt; {X,Y}.<br>{aaa,bbb}<br><br>it works.<br><br>Robert<br><br><div class="gmail_quote">2008/11/15 damien morton <span dir="ltr">&lt;<a href="mailto:dmor...@bitfurnace.com">dmor...@bitfurnace.com</a>&gt;</span><br>
<blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;"><div>1&gt; case [] of [] -&gt; X = aaa; X -&gt; ok end.</div><div>aaa</div><div>2&gt; case bbb of [] -&gt; X = aaa; X -&gt; ok end.</div>
<div>** exception error: no case clause matching bbb</div><div><br></div><div>am I missing something?</div>
<br><div class="gmail_quote">On Sun, Nov 16, 2008 at 4:42 AM, mats cronqvist <span dir="ltr">&lt;<a href="mailto:ma...@kreditor.se" target="_blank">ma...@kreditor.se</a>&gt;</span> wrote:<br><blockquote class="gmail_quote" style="border-left: 1px solid rgb(204, 204, 204); margin: 0pt 0pt 0pt 0.8ex; padding-left: 1ex;">

<div><br>
</div> &nbsp;strangely, this also works;<br>
<br>
case foo() of<br>
 &nbsp;[] -&gt; X = bar();<br>
 &nbsp;X -&gt; ok<br>
end<br>
<br>
 &nbsp;as long as X is bound in each clause, you&#39;re golden.<br>
<br>
 &nbsp;this might qualify as a gotcha.<br>
<font color="#888888"><br>
 &nbsp;mats<br>
</font></blockquote></div><br>
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