Re: [boost] [proto] Problems with operator <<

Subject: Re: [boost] [proto] Problems with operator <<
From: Eric Niebler (eric_at_[hidden])
Date: 2011-08-26 08:21:28

On 8/26/2011 3:32 AM, John Maddock wrote:
>>> BTW I do specify a proto grammar, and only enable the operators I need
>>> on a case by case basis, in this case though I would need to restrict
>>> the grammar so that proto's shift operators are only enabled for RHS
>>> arguments of integer type.   Is that possible?
>>
>> Yes. Can you post your grammar?
> 
> Pretty basic at present, need to refine those terminals a bit more! :

Yes!

> struct big_number_grammar
>  : proto::or_<
>        proto::terminal< proto::_ >

You correctly identified your problem with the stream operators.
std::cout matches because of the above line, and it shouldn't.

>      , proto::plus< big_number_grammar, big_number_grammar >
>      , proto::multiplies< big_number_grammar, big_number_grammar >
>      , proto::minus< big_number_grammar, big_number_grammar >
>      , proto::divides< big_number_grammar, big_number_grammar >
>      , proto::unary_plus< big_number_grammar >
>      , proto::negate< big_number_grammar >
>      , proto::modulus<big_number_grammar, big_number_grammar>
>      , proto::shift_left<big_number_grammar, big_number_grammar>
>      , proto::shift_right<big_number_grammar, big_number_grammar>
>    >
> {};
> 
> I assume I could replace
> 
>      , proto::shift_right<big_number_grammar, big_number_grammar>
> 
> with something like:
> 
>      , proto::shift_right<big_number_grammar, integer_terminal>
> 
> Where integer_terminal is a big list of terminal integer types, but is
> there any way to use a predicate to say "any type that matches predicate
> X is a terminal"?

Yes. You want:

  // Match any integral terminal
  proto::and_<
    proto::terminal< proto::_ >,
    proto::if_ < boost::is_integral< proto::_value >() >
  >

HTH,

-- 
Eric Niebler
BoostPro Computing
http://www.boostpro.com