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Date: Tue, 23 Nov 2004 00:16:31 -0500
From: Hans Gilde <hgilde-commons@earthlink.net>
Subject: RE: [jira] Created: (JELLY-163) Allow Expressions to throw exceptions
In-reply-to: <1C9FEAF0-36EF-11D9-B323-000A95C50B1C@activemath.org>
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Paul,

For most tags, expressions are evaluated at runtime, but immediately =
before
the tag itself becomes aware of them. They're evaluated by the enclosing
TagScript (a Script that runs a Tag) immediately before the tag itself =
is
run. The tag just knows about the result of the expression, not the =
actual
evaluation.

An exception at this time could be caught by the enclosing tag, but not =
by
the tag that should have received the expression. So, there's currently =
no
generic way to have a tag say "don't worry about expression evaluation
failures, just show me the contents/null/whatever".

Your example would work fine, the exception would be thrown out of the
script or could be caught by an enclosing tag.

Hans

-----Original Message-----
From: Paul Libbrecht [mailto:paul@activemath.org]=20
Sent: Monday, November 15, 2004 5:14 AM
To: Jakarta Commons Developers List
Subject: Re: [jira] Created: (JELLY-163) Allow Expressions to throw
exceptions

Hans,

I think this is exactly what made me stumble... I don't really get=20
this...
(I'm again about my fuzzyness of understanding jelly lifecycle... sorry=20
for this!). I see two times where such an exception can occur:
- at compilation time. This should be the same when a tag would meet=20
unknown attributes or a (strict) taglib would meet an unknown tag.
- at execution time, when the expression should return something=20
(maybe).
In both cases, the exception should be thrown and wrapped into some=20
generic exception which should include location information.

My current attempt was the script:
<j:jelly xmlns:j=3D"jelly:core">
     <j:set var=3D"b" value=3D"blop"/>
     ${b-'b'}
</j:jelly>
Which did throw me an exception (as I instructed it) but which was not=20
caught, or wrapped...

In which of the two phases should such a thing be caught ?
Are there other phases ?

thanks

paul


Le 15 nov. 04, =E0 02:32, Hans Gilde (JIRA) a =E9crit :

> Expressions are evaluated before the tag is run, so it normally=20
> wouldn't know anything about them.


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