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<div class="moz-cite-prefix">On 02/18/2013 02:35 PM, Geoffrey De
Smet wrote:<br>
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<blockquote cite="mid:kftame$8md$1@ger.gmane.org" type="cite">
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<div class="moz-cite-prefix">Op 18-02-13 14:00, Willem van Asperen
schreef:<br>
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<blockquote cite="mid:512225DC.10205@van.asperen.org" type="cite">
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<div class="moz-cite-prefix">On 02/18/2013 11:11 AM, Willem van
Asperen wrote:<br>
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<blockquote cite="mid:5121FE52.90301@van.asperen.org"
type="cite">
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Hi All,<br>
<br>
Just wanted to share with you an easy mistake. This is done
running Drools 5.5.0.Final.<br>
<br>
Imagine a fact<br>
<br>
<code>Cheese (</code><code><br>
</code><code> creationTick : double</code><code><br>
</code><code> preservationTicks : double</code><code><br>
</code><code>)</code><br>
<br>
Then the following does not do what you expect:<br>
<br>
<code>rule "dump old cheese"</code><code><br>
</code><code> when</code><code><br>
</code><code> $c : Cheese( $sbd : creationTick +
preservationTicks )</code><code><br>
</code><code> CurrentTime( tick >= $sbd )</code><code><br>
</code><code> then</code><code><br>
</code><code> System.out.println("</code><code>we have
to dump "+$c);</code><code><br>
</code><code>end</code><br>
<br>
You would expect that $c is dumped when current time has
passed creationTick + preservationTicks. But no. The variable
$sbd is bound to creationTick <i>before</i> the
preservationTicks are added!! I must say that I do not quite
understand how ($sbd : creationTick) + preservationTicks
resolves to "true" to make the premise succeed... Maybe
because it is != 0?<br>
<br>
I found that it should be:<br>
<br>
<code>rule "dump old cheese"</code><code><br>
</code><code> when</code><code><br>
</code><code> $c : Cheese( $sbd : (creationTick +
preservationTicks) )</code><code><br>
</code><code> CurrentTime( tick >= $sbd )</code><code><br>
</code><code> then</code><code><br>
</code><code> System.out.println("we have to dump
"+$c);</code><code><br>
</code><code> end</code><br>
<br>
This makes sense. Now $sbd is bound to the result of the
addition. But it is an easy trap!!<br>
<br>
Regards,<br>
Willem<br>
</blockquote>
Hi All,<br>
<br>
Coming back to this... What will be evaluated in the following
snippet:<br>
<br>
rule "dump old cheese"<br>
when<br>
CurrentTime( $tick : tick )<br>
$c : Cheese( $tick >= creationTick +
preservationTicks )<br>
then<br>
System.out.println("we need to dump "+$c);<br>
end<br>
<br>
I assume this evaluates if $tick is larger or equal to
(creationTick + preservationTicks), right?</blockquote>
I think so too.<br>
It looks like the : operator has a higher precedence then + (and
therefor >= too), which is a bit surprising indeed.<br>
Personally, I never mix the : operator with other operators, to
avoid having to worry about the precendence.<br>
</blockquote>
So you would write:<br>
<br>
<code>rule "dump old cheese"</code><code><br>
</code><code> when</code><code><br>
</code><code> $c : Cheese( $ct : creationTick, $p :
preservationTicks )</code><code><br>
</code><code> CurrentTime( tick >= $ct + $p )</code><code><br>
</code><code> then</code><code><br>
</code><code> System.out.println("we have to dump "+$c);</code><code><br>
</code><code> end<br>
</code> <br>
Assuming + takes precedence over >=.<br>
<br>
The reason I am binding the sum to creationTick and
preservationTicks to a variable is that I am using that variable in
multiple places and do not want the engine to have to calculate the
sum for every occurrence. Also: it makes the rule more readable in
my view.<br>
<blockquote cite="mid:kftame$8md$1@ger.gmane.org" type="cite">
<blockquote cite="mid:512225DC.10205@van.asperen.org" type="cite">
Otherwise it would say<br>
<br>
step 1: $tick > creationTick + preservationTicks<br>
step 2: true + preservationTicks<br>
<br>
which would fail, obviously because you cannot add a double to a
boolean.<br>
<br>
Regards,<br>
Willem<br>
<br>
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