Re: [JEXL] Blocks and an Expression

[Rahul Akolkar <ra...@gmail.com>]

On 2/27/06, Dion Gillard <di...@gmail.com> wrote:
> Ok, I've found the cause of the problem.
>
> ExpressionFactory.createNewExpression on line 125 does this:
>
>        SimpleNode node = (SimpleNode) tree.jjtGetChild(0);
>
> So only the first statement of the parsed expression is actually evaluated.
>
> In the cases of the commented out tests, there are multiple statements which
> are children of the parse tree.
>
> The use of a block here really isn't significant, using a parse string like
> "x =1; y=2;" causes the same issue.
>
<snip/>

Agreed.

> So, the question becomes, should we support multiple statements for an
> expression (outside a block), or do we implement ASTJexlScript so that it
> evaluates each of it's children in turn and returns the last value?
>
<snap/>

Neither? ;-) Took a peek, the behavior is as advertised since a JEXL
Expression is indeed a reference to a single expression, and those
semantics need to persist. However, since we use the "script grammar"
for the ExpressionFactory (whereas the grammar for scripts is really a
superset of the expression grammar), we parse the (potential) script
and pluck out the just first expression even if there are more. The
fact that expressions beyond the first are silently ignored probably
needs to be addressed. Short of teasing apart two grammars (and/or
having a ScriptFactory), perhaps it will be sufficient to trivially
log a warning when that happens.

WDYT?

As an independent question, why doesn't JEXL have Script as a first
class entity like Expression (with a ScriptFactory to match)?

-Rahul

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Re: [JEXL] Blocks and an Expression

[Dion Gillard <di...@gmail.com>]

On 3/1/06, Rahul Akolkar <ra...@gmail.com> wrote:
<snip>
>
> > So, the question becomes, should we support multiple statements for an
> > expression (outside a block), or do we implement ASTJexlScript so that
> it
> > evaluates each of it's children in turn and returns the last value?
> >
> <snap/>
>
> Neither? ;-) Took a peek, the behavior is as advertised since a JEXL
> Expression is indeed a reference to a single expression, and those
> semantics need to persist. However, since we use the "script grammar"
> for the ExpressionFactory (whereas the grammar for scripts is really a
> superset of the expression grammar), we parse the (potential) script
> and pluck out the just first expression even if there are more. The
> fact that expressions beyond the first are silently ignored probably
> needs to be addressed. Short of teasing apart two grammars (and/or
> having a ScriptFactory), perhaps it will be sufficient to trivially
> log a warning when that happens.


A warning would be a good idea. I don't want to change the behaviour of
Expression to throw an exception if there is more than a single piece.

WDYT?
>
> As an independent question, why doesn't JEXL have Script as a first
> class entity like Expression (with a ScriptFactory to match)?


This sounds like a good thing to add to 1.1 - Loading and executing scripts.

-Rahul
>
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