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Re: Ambiguity involving two parse stacks reducing on the same rule


From: Laurence Finston
Subject: Re: Ambiguity involving two parse stacks reducing on the same rule
Date: Thu, 10 Mar 2005 15:58:28 +0100 (MET)

> > v: e
> >  | e e
> >
> > e: 'a'
> >  | 'a' 'a'
> >

> [...] my question was if there was a way
> to get `%dprec' to work in such a case without having to rearrange
> the grammar. This question still stands, and perhaps someone here
> has an idea ...?

Perhaps structuring your grammar in a way similar to the following
example would help to solve your problem.  This is just off the
top of my head, so I don't know if it will work, and
you would probably have to fiddle with it.

v_primary:   (Whatever)
           | e_primary

v_secondary:   v_primary
             | e_secondary e_primary

v_tertiary:  v_secondary

v_expression: v_tertiary

e_primary: 'a'

e_secondary:   e_primary
             | e_secondary e_primary

e_tertiary: e_secondary

e_expression: e_tertiary

I think of the rules
`v_secondary:  e_secondary e_primary'
and
`e_secondary: e_secondary e_primary'
as being operations with an implied operator between the symbols on
the right-hand side.

I use this technique (which I borrowed from Knuth) for my grammar.

Laurence Finston
http://www.gnu.org/software/3dldf/LDF.html




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