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IExpressionEvaluator Questions [message #1821878]

Fri, 21 February 2020 09:30

Eclipse User

I'm trying out the tutorial and I was wondering how one can create patterns with Java.

The documentation of the IExpressionEvaluator states that it can be used to execute arbitrary java code for the pattern matching, as long as we correctly give back all parameter names with getInputParameterNames().

Does this mean that we can thus use any java-defined pattern with Rete's / LocalSearch as long as it only depends on the input parameters? Are there any caveats?

Re: IExpressionEvaluator Questions [message #1821883 is a reply to message #1821878]

Fri, 21 February 2020 10:29

Eclipse User

Hi Hans,

as you have written the Java code must _only_ depend on the input parameters and be deterministic, but otherwise anything that compiles should work. The planning assumes that the evaluation of a given expression is fast thus the evaluation is often done as soon as possible (but breaking this assumption "only" results in suboptimal performance). Two important corner cases (but still consistent with the previous semantics):

(1) if the code throws an exception (e.g. division by zero), it is considered not matching.
(2) the code should not expect any specific evaluation order - the evaluator will only be called for inputs the matcher considers potential match for the pattern in the order it finds them.

Best regards,
Zoltán

Re: IExpressionEvaluator Questions [message #1821884 is a reply to message #1821878]

Fri, 21 February 2020 10:36

Eclipse User

Hi Hans,

also, calling custom Java functions is available is possible not only using the IExpressionEvaluator API, but also through the VQL language as well:
https://www.eclipse.org/viatra/documentation/query-language.html#!#_function_whitelist

Best,
Gábor

Re: IExpressionEvaluator Questions [message #1821892 is a reply to message #1821884]

Fri, 21 February 2020 11:06

Eclipse User

Hello,

That's great to hear! I'm considering using Viatra for my master thesis and that was the make-or-break feature.

Kind regards,

Hans

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