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https://issues.apache.org/jira/browse/JENA-270?page=com.atlassian.jira.plugin.system.issuetabpanels:comment-tabpanel&focusedCommentId=13400420#comment-13400420
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Andy Seaborne commented on JENA-270:
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> CALL with no argument returns null.
Expressions really should not return null. The contract is value or eval
failure. The code is quite protective (FILTER) but it's not the contract.
COALESCE(CALL(),1) breaks (ARQInternalErrorException).
Either CALL() should be a syntax error, a defined value, or throw
ExprEvalException.
Either a syntax error or returning "true" (do nothing) makes sense to me.
> Support dynamic function invocation in ARQ
> ------------------------------------------
>
> Key: JENA-270
> URL: https://issues.apache.org/jira/browse/JENA-270
> Project: Apache Jena
> Issue Type: New Feature
> Components: ARQ
> Affects Versions: ARQ 2.9.2
> Reporter: Rob Vesse
> Assignee: Rob Vesse
> Labels: call, dynamic, functions, sparql
> Fix For: ARQ 2.9.2
>
>
> Per my suggestion to the SPARQL Working Group I am proposing a new built in
> CALL() which can be used in SPARQL queries for dynamic function invocation.
> CALL with no argument returns null
> CALL with some arguments evaluates the first argument, sees if the result is
> a URI (if not errors) and if so tries to generate a function from it and
> invoke it with the arguments to that invocation being the remaining arguments
> to CALL
> I have implemented a prototype implementation of this in the ARQ language
> which I have committed to Trunk, others with more knowledge of expression and
> function evaluation in ARQ may have suggestions on how to improve the
> implementation
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