[antlr-interest] TokenStreamRewriteEngine: possible to use non-terminals instead of tokens?

[SainTiss]

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On Wednesday 04 February 2004 22:41, Terence Parr wrote:
> On Feb 4, 2004, at 1:31 PM, SainTiss wrote:
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> > I must be misunderstanding this, because as far as I can see, this
> > won't work
> > in general...
> > Having a stack will work if there's a rule which calls itself directly
> > or
> > indirectly.
>
> The stack will handle the recursion properly.


Indeed it will... The problem I was referring too, however, is that it is not 
always so obvious whether a rule is going to be recursive or not (because 
there might be many alternative sub-rules, and in a large grammar, it's 
probably tedious to check which of them eventually calls the original rule 
again). And as I see it, it is necessary to find all points of recursion, 
because each of those has a potential of overwriting the top of stack...

>
> identifier will set the attribute value and you are free to use it at
> the appropriate time.  In your myRule example, you need to make a copy
> of the index value before it calls identifier again.  This is
> simulating what a return value bubbling up would do.  It's set below,
> but each reference has a copy.  The instance variable approach avoids
> the problem of having to define the return value in all the
> intermediate rules and the stack avoids the "what about recursive rule
> ref" problem.

That will work as well, with the same problem as above: you need to be sure 
which sub-rules will eventually call "identifier", and make a copy for each 
of them. But it may be needed to make copies in sub-rules too, if they 
themselves call "identifier" multiple times, and so on...

So in conclusion, I guess it will work, but analyzing where pushes and pops 
and copies need to be made, is going to be almost as bad as having to pass a 
parameter...

Unless of course I'm overlooking something again, but I think I could make an 
example illustrating this if needed...

Thanks,

Hans

>
> Hope this helps...
>
> Ter
> --
> Professor Comp. Sci., University of San Francisco
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