Re: Bison and an one-parse interpreter

[pkamath]

Hello,


We have been using Flex/Bison for our parsing needs in our project.
We are currently facing a problem which is a generic problem that some of
you might have
come across. Let me explain the problem:-

I have a rule


a: Token1 Token2
{
     /*Non recoverable operation*/
}

Now if I have a input set of tokens like

Token1 Token2

things are fine

But if I have a input set of tokens like

Token1 Token2 #
(where # is a forbidden token)

Then first the action code for rule a is executed and then the error
handler for the parser is invoked since
there is a token that is not accepted by the parser.

The problem is once the action code for a is executed then this cannot be
recovered from.
How do we handle this kind of a case?

Is there any way that we can give a rule in bison like

a: Token1 Token2 NOTHINGMORE


which means the tokens must reduce to a *only if* you have
input tokens Token1 Token2 << and nothing after that>>.

This being a basic design problem we would like a fix that would not
require us to
modify our rules much.

Any suggestions/input would go a long way in helping us.
Thanking u for ur valuable time.

With Regards
R.Kamath





Jeppesen Hans Mejdahl <address@hidden> on 08/02/2002 10:38:38 AM

To:   "'address@hidden'" <address@hidden>
cc:    (bcc: P Raghavendra Kamath/HSSBLR)

Subject:  Bison and an one-parse interpreter




Hi there...

I want to build a one-parse interpreter using flex/bison is this possible?

As I see it: simpel expresion and asignments works fine,
BUT: condition and loops :-(

Consider this test "gramma":

     if-stmt : IF if-bool THEN true-stmt;
              {dont-do=0;};

            if-bool : bool:
                { don't-do=1;
                   $=$1;
                };

     stmt: id '=' value
               {if (!dont-do) setvalue($1,$3) };

This might workbut look like h.... !
And what about a loops ?

Regards Hans M Jeppesen



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