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<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Right.&nbsp; Still, it&#8217;s a point worth noting. I&#8217;ve added a short
section to<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp;&nbsp; <a
href="http://hackage.haskell.org/trac/haskell-prime/wiki/BangPatterns">http://hackage.haskell.org/trac/haskell-prime/wiki/BangPatterns</a><o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>which in turn is referred to from the GHC manual.<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'>Simon<o:p></o:p></span></p>

<p class=MsoNormal><span style='font-size:11.0pt;font-family:"Calibri","sans-serif";
color:#1F497D'><o:p>&nbsp;</o:p></span></p>

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<p class=MsoNormal><b><span lang=EN-US style='font-size:10.0pt;font-family:
"Tahoma","sans-serif"'>From:</span></b><span lang=EN-US style='font-size:10.0pt;
font-family:"Tahoma","sans-serif"'> haskell-bounces@haskell.org
[mailto:haskell-bounces@haskell.org] <b>On Behalf Of </b>Lennart Augustsson<br>
<b>Sent:</b> 18 November 2007 22:47<br>
<b>To:</b> Derek Elkins<br>
<b>Cc:</b> Haskell users<br>
<b>Subject:</b> Re: [Haskell] Bang patterns and declaration order<o:p></o:p></span></p>

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<p class=MsoNormal><o:p>&nbsp;</o:p></p>

<p class=MsoNormal style='margin-bottom:12.0pt'>I totally agree with
Derek.&nbsp; Which exception you get can vary with compiler version, compiler
flags, time of day, phase of the moon, ...<br>
It will be one in a set of exceptions, but you don't know which one.<br>
<br>
&nbsp; -- Lennart <o:p></o:p></p>

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<p class=MsoNormal>On Nov 18, 2007 8:34 PM, Derek Elkins &lt;<a
href="mailto:derek.a.elkins@gmail.com">derek.a.elkins@gmail.com</a>&gt; wrote:<o:p></o:p></p>

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<p class=MsoNormal style='margin-bottom:12.0pt'>On Sun, 2007-11-18 at 12:11
-0800, Iavor Diatchki wrote:<br>
&gt; Hello,<br>
&gt;<br>
&gt; I was playing around with &quot;bang patterns&quot; and I noticed that<br>
&gt; when combined with asynchronous exceptions they can lead to <br>
&gt; programs where the order of the declarations in a binding<br>
&gt; group is important! &nbsp;Here is an example:<br>
&gt;<br>
&gt; &gt; import Control.Exception<br>
&gt; &gt; import Prelude hiding (catch)<br>
&gt; &gt;<br>
&gt; &gt; main = putStrLn =&lt;&lt; eval_order<br>
&gt; &gt;<br>
&gt; &gt; test = &quot;no exception&quot;<br>
&gt; &gt; &nbsp; where !_ = error &quot;top down&quot;<br>
&gt; &gt; &nbsp; &nbsp; &nbsp; &nbsp; !_ = error &quot;bottom up&quot;<br>
&gt; &gt; <br>
&gt; &gt; eval_order = evaluate test `catch` \e -&gt;<br>
&gt; &gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;case e of<br>
&gt; &gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;
&nbsp;ErrorCall txt -&gt; return txt<br>
&gt; &gt; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp;_
&nbsp; &nbsp; &nbsp; &nbsp; &nbsp; &nbsp; -&gt; throw e<br>
&gt; <br>
&gt; Of course, this is a contrived exampled but, as far as I know,<br>
&gt; this was not possible in Haskell before (if anyone has an example<br>
&gt; to the contrary please send it to the list).<br>
&gt;<br>
&gt; By the way, with GHC 6.8.1 the above program prints &quot;bottom up&quot;.<br>
&gt; This means that when there are multiple &quot;banged&quot; bindings they<br>
&gt; are evaluated starting with the last one in the text. &nbsp;I imagine<br>
&gt; than in most programs this is not particularly important, but <br>
&gt; it seems to me that it would be a bit nicer if we were to adjust<br>
&gt; the translation so that bindings were evaluated top to bottom<br>
&gt; (e.g., like in ML).<o:p></o:p></p>

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<p class=MsoNormal>The whole point of the &quot;imprecise exceptions&quot;
paper was that any <br>
exception may be returned when multiple ones could be. &nbsp;There is no<br>
reason why the bindings should be evaluated top-down. &nbsp;If you are<br>
relying on the order the bindings are evaluated you are doing something<br>
very, very wrong. &nbsp;Should we also specify what exception should be <br>
thrown for &nbsp;error &quot;left-right&quot; + error &quot;right-left&quot; ?<o:p></o:p></p>

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<p class=MsoNormal><br>
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<p class=MsoNormal><o:p>&nbsp;</o:p></p>

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