Subject: Re: [Boost-users] [Proto] implementing an computer algebra system with proto
From: Kim Kuen Tang (kuentang_at_[hidden])
Date: 2009-01-30 18:23:48
Dave Jenkins schrieb:
>
> "Kim Kuen Tang" <kuentang_at_[hidden]> wrote in message
> news:497F760C.1030408_at_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