Re: [boost] Re: [ANN] Spirit C++ parser framework.

From: joel de guzman (isis-tech_at_[hidden])
Date: 2001-06-01 20:55:36

From: "David Abrahams":
>
> > a | b       Union (match a or b. Also referred to as alternatives)
>
> OK.
>
> > a & b     Intersection (match a and b)
>
> Haven't been following closely, but what does this mean? Is it the same as
> "ab" in conventional BNF? or perhaps "ab|ba" ?
>
> > a - b      Difference (match a but not b)
> > a ^ b      XOR (match a or b, but not both)
>
> Likewise, what does it mean to match "both"?
>
> -Dave

See the link to Dr. Dick Botting on XBNF:
How far can BNF stretch. Dr. Botting gave some
insights and proof that Intersections let us define languages
that are not context free:
http://www.csci.csusb.edu/dick/papers/rjb93a.xbnf.html

a & b

Indicates that all the descriptions of a and b must hold
at once (set intersection), not in sequence.

a ^ b

Is somewhat similar to | (set union, alternatives)
with the added restriction that only one (not both)
should hold.

... just your basic boolean algebra truth tables applied to
parsing.

-Cheers,
Joel de Guzman