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

From: joel de guzman (isis-tech_at_[hidden])
Date: 2001-05-28 00:16:30

> --- In boost_at_y..., Douglas Gregor <gregod_at_c...> wrote:

> I know this, and I'm assuming there are two forms for repetition:
> 
> e[N] - Repeat "e" exactly N times
> e[X][Y] - Repeat "e" at least X and at most Y times (Y can be 
> infinity).
> 
> Using the bracket operator for this creates an ambiguity with, for 
> instance:
> 
> e[X][Y]
> 
> This could be read as "repeat `e' at least X and at most Y times" 
> or "repeat 
> `e' X times and then repeat that Y times." If we instead use a syntax 
> where 
> there is a comma between X and Y, then we've surely differentiated 
> between 
> two repetition forms (e[X][Y] is obviously different than e[X, Y]). 
> Brackets 
> unfortunately won't let us do that, but the function call operator() 
> will, as 
> will free functions.
> 
> Doug

Ahh OK. you mean 'ambiguity' from the client's perspective.
OK, load and clear.

Pardon my inquisitive nature. How about:

a[8];                   // exactly 8 times
a[0, more];         // you said can be done, i believe so (comma (,) op)
a[0, until(15)];    // likewise can be done

we can even have:

a[from(0), until(10)] for people who prefer verbosity.

Why the fuss? I want iteration to be very distinct from grouping. Too many
parentheses make the code quite difficult to read except for lisp/scheme
folks. 

Thanks,
Joel de Guzman