RE: [xsl] saxon:try()

Subject: RE: [xsl] saxon:try()
From: "Michael Kay" <mike@xxxxxxxxxxxx>
Date: Fri, 4 Jan 2008 14:59:50 -0000
>     Florent>   But I think that the ex:error-safe instruction should
>     Florent> be exactly predictable, deterministic.  If an expression
>     Florent> stands lexically outside of the instruction, if it
>     Florent> produces an exception, it shouldn't be caught (but that's
>     Florent> only my humble point of view).
> But that goes against the declarative nature of XSLT.
> xsl:variable declares the definition of a value. It doesn't 
> indicate execution at all.
> The reference to the variable, which is inside the ex:try, is 
> the most logical place to think of the evaluation occuring.

You can do it that way - treating a variable reference rather like a
function call - but it gets difficult if one reference to a variable is
inside a try/catch and another isn't (or is in a different try/catch). Do
you catch the error twice? 

I think it's easier to use the more conventional model where the variable is
treated as if it is eagerly evaluated. That doesn't actually stop lazy
evaluation internally - you just have to make the try/catch environment of
an expression part of the closure that you retain until the evaluation is
performed, just as you retain the other parts of its context already.

Michael Kay

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