[antlr-interest] validating semantic predicates

[Matt Benson]

That's one way... thanks.

-Matt

--- Ari Steinberg <ari.steinberg at embarcadero-ca.com>
wrote:
> I had a similar problem in my grammar.  To get
> around it, I caught the semantic exception and then
> throw a new one with a better error message.  My
> parser has a reference to the lexer so I created
> getLine() and getColumn() functions which return the
> current line and column the lexer so that the
> exception returns valid data.
> 
> myRule:
> ...
> ;
> exception
> catch[SemanticException ex]
> {
>     throw SemanticException( "Syntax error in
> Explain statement", getFilename(), getLine(),
> getColumn());
> }
> 
> Cheers,
> 
> Ari
> 
> -----Original Message-----
> From: Matt Benson [mailto:gudnabrsam at yahoo.com]
> Sent: Wednesday, June 18, 2003 2:45 PM
> To: Antlr List
> Subject: [antlr-interest] validating semantic
> predicates
> 
> 
> I have Tooled my grammar and it has generated a
> parser.  I have written the grammar to process the
> different elements of the file by calling methods on
> a
> registered implementation of a handler object. 
> Thus,
> I am currently concerned only with content.  I am
> providing the handler a Stack of relevant tokens in
> case something farther away than the current context
> is needed.  So every time I enter a rule, I push the
> primary token onto the stack (remember I'm dealing
> with XML so this is pretty straightforward), and pop
> it before I return from the rule.  I figure while
> I'm
> doing the pop, I might as well do a kind of sanity
> check by way of a validating semantic predicate:
> 
> {t == tokenStack.pop()}?
> 
> One thing I noticed right away is that the
> SemanticException thrown in the event that this is
> not
> true contains the exact text.  I don't see in the
> docs
> whether and how to customize this text; I am
> currently
> doing this:
> 
> {t == tokenStack.pop() /*unexpected token on the
> stack*/}?
> 
> which is good enough, but I just wondered if there
> was
> a better way.
> 
> TIA,
> Matt
> 
> 
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