Subject: Re: [Boost-users] [Proto] implementing an computer algebra systemwith proto
From: Dave Jenkins (david_at_[hidden])
Date: 2009-01-28 16:55:21
"Kim Kuen Tang" <kuentang_at_[hidden]> wrote in message
news:4980CB95.2010706_at_vodafone.de...
> I see that this is a problem. (What does UB stand for?)
UB = Undefined Behavior (the compiler can crash, produce wrong results, or
anything else)
> But can a correct implemented grammar be a workaround?
The grammar was correct, but it was given an invald expression (that sort-of
looked valid).
> Perhaps we can first check whether var1_ appears in the expression. If not
> we can return the expression unmodified.
The way to check if the expression is valid for a grammar is something like
the code below.
I'm hoping Eric can automatically do this check when a compile-time debug
flag is defined.
Regards,
Dave Jenkins
template< typename Expr >
void Solve_check( Expr const & expr )
{
if ( !proto::matches< Expr, Solve >::value )
{
std::cout << "Expression does not match grammar\n\n";
}
}
int main()
{
Solve_check(var_ + 1 = 2);
proto::display_expr( var_ + 1 = 2 );
proto::display_expr( Solve()( var_ + 1 = 2 ) );
}