[antlr-interest] short circuiting further evaluation

[Jim Idle]

> -----Original Message-----
> From: antlr-interest-bounces at antlr.org [mailto:antlr-interest-
> bounces at antlr.org] On Behalf Of Loring Craymer
> Sent: Saturday, May 29, 2010 3:26 PM
> 
> Don't walk the tree to evaluate the expression; walk the tree to
> generate byte code and then interpret the byte code.  The overall
> problem then gets simpler and the resulting code runs faster.
> 

Especially as code generation is almost trivial these days with ASM or LLVM (depending on your needs). If you can live with the JVM, then just use ASM and let the VM deal with it.

While writing a tree based interpreter is a useful experiment and learning aid, I think that overall, interpreting via the tree is somewhat awkward. Just my opinion of course.

Jim


> --Loring
> 
> 
> 
> ----- Original Message ----
> > From: Jane Eisenstein <janee at softweave.com>
> > To: "Farr, John" <john.farr at medtronic.com>
> > Cc: "antlr-interest at antlr.org" <antlr-interest at antlr.org>
> > Sent: Sat, May 29, 2010 2:15:56 PM
> > Subject: Re: [antlr-interest] short circuiting further evaluation
> >
> > Thanks. Using gated semantic predicates nicely simplifies the logic
> in each rule
> > (while doubling the number of rules).
> 
> It doesn't stop the parse though
> > -- just the evaluation.
> 
> Is there a clean way to determine the
> > condition's final result and return it without having to complete the
> parse of
> > the entire expression?
> 
> Jane
> 
> 
> On May 28, 2010, at 10:22 AM,
> > Farr, John wrote:
> 
> > The message I posted on April 8 with the subject
> > "Processing/traversing a rule -- dealing with conditionals" may help
> > you.
> >
> > --John
> >
> >
> > -----Original
> > Message-----
> > From:
> > href="mailto:antlr-interest-bounces at antlr.org">antlr-interest-
> bounces at antlr.org
> > [mailto:
> > href="mailto:antlr-interest-bounces at antlr.org">antlr-interest-
> bounces at antlr.org]
> > On Behalf Of Jane Eisenstein
> > Sent: Friday, May 28, 2010 7:47 AM
> >
> > To:
> > href="mailto:antlr-interest at antlr.org">antlr-interest at antlr.org
> >
> > Subject: [antlr-interest] short circuiting further evaluation
> >
> >
> > I'm working with a simple expression grammar:
> >
> >
> > condition:    conditional_expression  EOF
> >
> >     ;
> >
> > conditional_expression
> >
> >     :    conditional_term
> >
> >         (  OR conditional_expression
> > )?
> >     ;
> >
> > conditional_term
> >
> >     :    conditional_factor
> >
> >         ( AND conditional_term  )?
> >
> >     ;
> >
> > conditional_factor
> >
> >     :    conditional_primary
> >
> >     |    NOT conditional_primary
> >
> >     ;
> >
> > conditional_primary
> >
> >     : ID
> >     | LEFT_PAREN
> > conditional_expression RIGHT_PAREN
> >     ;
> >
> >
> > At runtime, ID tokens evaluate to either true or false. Once it is
> clear the
> > condition as a whole will evaluate to either true or false, I'd like
> to stop the
> > evaluation and return the value of the condition. So far, all I've
> managed to do
> > is short-circuit further ID evaluations once an upper level outcome
> is
> > know.
> >
> > Is there a way to short circuit the entire parse? I'm not
> > sure how to even tell it would be time to do so.
> >
> > Jane
> >
> >
> >
> >
> >
> >
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