Beautiful!

How would a business user (non-programmer) write such a rule.

There's some evidence that it's difficult to "un-think" your procedural programming imprinting. A non-programmer might even have the edge over a programmer.

But rule programming isn't a silver bullet - lots of stuff to learn.

The only way I can think of is create a dsl sentence for this specific condition

Even so.

-W

From: Wolfgang Laun [wolfgang.laun@gmail.com]
Sent: 02/09/2012 05:02 PM CET
To: Rules Users List <rules-users@lists.jboss.org>
Subject: Re: [rules-users] How do I write a rule to detect a missing value in a group of facts?

Don't think procedurally, just write the *rule* for a missing post ;-)

rule "missing fence post"
when
FencePost( $d: distanceFromStart )
FencePost( distanceFromStart == $d + 2*FencePost.GAP )
not FencePost( distanceFromStart == $d + FencePost.GAP )
then
System.out.println( "Missing: " + ($d + FencePost.GAP) );
end

-W

On 9 February 2012 16:41, mikeg <mike@thegoldners.com> wrote:
I need to write a rule to identify a missing element in a group of facts.

For example, let us say I want to ensure that my fence has a fence post
every 8 feet. My fact declaration is as follows:

declare FencePost
identifier : String
distanceFromStart: Long
end

If I add the following facts into my session:

FencePost("a", 0)
FencePost("x", 8)
FencePost("e", 24)

I want a rule that will notify the user that there is a missing fence post
between "x" and "e".

I've been looking into using "collect" into a TreeSet/TreeMap to get a
collection sorted on the "distanceFromStart", but I cannot figure out how to
compare adjacent elements in the collection.

Any ideas?

--
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