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

From: joel de guzman (joel_at_[hidden])
Date: 2001-05-22 19:03:45

----- Original Message -----
From: "David Abrahams":
> Only that sequencing is the most common operation, so it should have the
> simplest syntax. Since we can't get by with no syntax at all, I don't mind
> writing
>
> repeat<0>(a) meanting a*
> repeat<1>(a) meaning a+
> repeat<3,5>(a) meaning aaa | aaaa | aaaaa
>

I still want to keep the prefix +. EBNF and RegEX people are
already so a accustomed with the + for positive closure. One of
my goals was to mimic EBNF syntax as much as possible.
I guess c++ guys wouldn't be so bothered having prefix + for
the positive closure. We have the prefix * and infix * that does
different things already. We're used to that. So I'd say:

+(a + b);   // repeat a b zero to zillion times

Still the iterator syntax is nice. I'd say:

loop<0,8>(a);    //    0 ~ 8
loop<8>(a);       //    exactly 8 times (very useful for parsing files)
loop<0,_>(a);    //    zero to infinity (same as kleene star)
loop<1,_>(a);    //    one to infinity (same as positive closure)
loop<0,1>(a);    //    zero or one (same as optional closure)

** The single underscore means: to infinity and beyoooond....

I've been using a variant of this iterator in another parser generator.
I am rebuilding that right now on top of Spirit.

Joel de Guzman