Dave Jenkins schrieb:
"Kim Kuen Tang" <kuentang@vodafone.de> wrote in message news:497F760C.1030408@vodafone.de...
Hi Kim Tang,
I think the attached program solves that problem.
The problem I've been working on is to use the distributive law to simplify expressions at compile time. For example, I'd like to transform "var_ * 2 + var_ * 3 = 4" to "var_ * (2 + 3) = 4". Then, you could transform it to "var_ = 4 / (2 + 3)", all at compile time. Wouldn't that be cool? I think it's possible using Proto, but I haven't worked out the details yet. Any suggestions are welcome.
Hi Dave, thank you for the code. The grammar looks great. Here is a grammar that is able to perform the distributive law. It is not perfect because it doesnt cover all expressions. struct DistributiveLaw : proto::or_< // Solved: proto::multiplies<proto::terminal<placeholder>, _> // Rewrite "var_ *3+var_*2 to var_*(3+2)" , proto::when< proto::plus< proto::multiplies<proto::terminal<placeholder> ,proto::terminal<_> > ,proto::multiplies<proto::terminal<placeholder> ,proto::terminal<_> > > //, proto::_make_multiplies( proto::terminal<placeholder> , proto::_make_plus( proto::_right, proto::_left ) ) ,proto::_make_multiplies(proto::_left(proto::_left), proto::_make_plus(proto::_right(proto::_left),proto::_right(proto::_right) ) ) >
{};
struct Solve : proto::or_< // Solved: proto::assign<proto::terminal<placeholder>, _> // Rewrite "var_ + x = y" to "var_ = y - x" , proto::when< proto::assign< proto::plus< proto::terminal<placeholder>, _>, _ > , proto::_make_assign( proto::_left(proto::_left) , proto::_make_minus( proto::_right, proto::_right(proto::_left) ) ) >
I am not sure wheter this line is needed.
// Rewrite "x + var_ = y" to "var_ = y - x" , proto::when< proto::assign< proto::plus< _, proto::terminal<placeholder>>, _ > , proto::_make_assign( proto::_right(proto::_left) , proto::_make_minus( proto::_right, proto::_left(proto::_left) ) ) > // Rewrite "x + ? = y" to "Solve(? = y - x)" , proto::when< proto::assign< proto::plus< proto::terminal<_>, _>, _ > , Solve( proto::_make_assign( proto::_right(proto::_left) , proto::_make_minus( proto::_right, proto::_left(proto::_left) ) ) ) > // Rewrite "? + x = y" to "Solve(? = y - x)" , proto::when< proto::assign< proto::plus< _, proto::terminal<_> >, _ > , Solve( proto::_make_assign( proto::_left(proto::_left) , proto::_make_minus( proto::_right, proto::_right(proto::_left) ) ) ) >
{};
Cheers Kim