Re: [Boost-users] Spirit and semantic action with int_p (boost 1.34.1)

From: Hansi (hansipet_at_[hidden])
Date: 2008-05-16 10:14:51

thank you very much for the help.

Hartmut Kaiser schrieb:
> Hi,
> 
>> I have a problem with a sematic action when I use int_p.
>>
>> I have the following declaration:
>>
>> array_declaration =
>> 	confix_p(LEFT_BRACKET, int_p[new_int] ,RIGHT_BRACKET);
>>
>> and new_int is defined in the following way:
>>
>> typedef function< void( int )                      > Int_action;
>> Int_action  new_int       ( bind( &SemanticActions::new_int,
>> &self.actions_, _1 ) );
>>
>> in this case I get allways (VS2005) the error message:
>> Error	1	error C2064: term does not evaluate to a function taking 2
>> arguments
>> C:\Programme\boost\boost_1_34_1\boost\spirit\core\scanner\scanner.hpp
>> 	146
>>
>> if I use instead of the Int_action a action
>>
>> typedef function< void( const char*, const char* ) > Str_action;
>>
>> I have no errors during compiling.
>>
>> What I make wrong?
> 
> The answer is quite tricky.
> The confix_p parser does a internal refactoring of the wrapped parser
> expression, i.e. 
> 
>     confix_p(l, int_p[f], r) 
> 
> get's refactored to 
> 
>     l >> (int_p - r)[f] >> r
> 
> This is done to make the confix_p parser do what's expected even in the
> general case.
> Here is the corresponding comment from the confix.hpp file:
> 
> //      If the body parser is an action_parser_category type parser (a
> parser
> //      with an attached semantic action) we have to do something special.
> This
> //      happens, if the user wrote something like:
> //
> //          confix_p(open, body[f], close)
> //
> //      where 'body' is the parser matching the body of the confix sequence
> //      and 'f' is a functor to be called after matching the body. If we
> would
> //      do nothing, the resulting code would parse the sequence as follows:
> //
> //          start >> (body[f] - close) >> close
> //
> //      what in most cases is not what the user expects.
> //      (If this _is_ what you've expected, then please use the confix_p
> //      generator function 'direct()', which will inhibit
> //      re-attaching the actor to the body parser).
> //
> //      To make the confix parser behave as expected:
> //
> //          start >> (body - close)[f] >> close
> //
> //      the actor attached to the 'body' parser has to be re-attached to the
> //      (body - close) parser construct, which will make the resulting
> confix
> //      parser 'do the right thing'. This refactoring is done by the help of
> //      the refactoring parsers (see the files refactoring.[hi]pp).
> 
> Well, in your case it's not exactly what you've been expecting and this
> refactoring isn't needed (because RIGHT_BRACKET is not a possible subset of
> any of the possible int_p matches).
> 
> As the comment says, you can prevent this refactoring by just writing:
> 
>     confix_p.direct(LEFT_BRACKET, int_p[new_int], RIGHT_BRACKET)
> 
> instead.
> 
> HTH
> Regards Hartmut
> 
> PS: Please direct future inquiries wrt Spirit to the Spirit mailing list.