Re: x + (y) + z

[Derek M Jones]

Hans,

>You ignore the context information distinguishing between type-names and
>number-names. So set these names equal to the same token, and let the GLR
>parser handle it. It then produces all correct parses, including the
>possible type-name/number-name choices.

This is what I am already doing (I have no choice since there is
no symbol table).

> You then get the correct parse
>trees, and need only decide how to select one over the other. Clearly, this
>choice cannot be done, in general, unless you somehow supply the context
>information missing.

Unfortunately glr parsing is not a universal solution.  It requires that
at the end of processing there be a unique parse tree (the multiple
parse trees that may exist while processing the input tokens are required
to eventually resolve to a single parse).

The %dprec option allows the grammar writer to select which parse to use
in some circumstances (i.e., both parses must involve the same sequence
of tokens), but not all.

I am current trying to figure out why

(x) + (y) + z;

(which can be parsed in four different ways) is generating an ambiguity
(it should be handled by my existing uses of %dprec and grammar
rewrites)

derek

--
Derek M Jones                                     tel: +44 (0) 1252 520 667
Knowledge Software Ltd                         mailto:address@hidden
Applications Standards Conformance Testing   http://www.knosof.co.uk