Re: [Boost-users] [boost-users][[proto] : Seeking advice on a DSL

Subject: Re: [Boost-users] [boost-users][[proto] : Seeking advice on a DSL
From: Manjunath Kudlur (keveman_at_[hidden])
Date: 2010-03-17 22:47:41

> Tricky. I can imagine a scheme where, as you build the program expression,
> you walk the expression and keep a map<void*,int> from parameters addresses
> (e.g. int_*) to monotonically increasing slot numbers; as you go, you can
> replace the parameters with their slot numbers. You end up with a program
> where each "a" is replaced with "slot(0)", each "b" with "slot(2)" and each
> "c" with "slot(3)" (where "slot" is some type that wraps a runtime int).
> Later, when evaluating the program, the parameters to the program are put in
> a std::vector, and the evaluator knows to evaluate "slot" terminals by
> indexing into the vector. Handling out parameters requires special handling,
> as would handling expressions where not all parameters have the same type.
>
> This is essentially the same as what you describe above, except the
> expensive mapping is done by the code the builds the program rather than the
> code that evaluates it.

Thanks, that does help. The other approach I was toying with was to
hold the values "in situ", i.e., make int_ contain the datum. The
biggest hurdle I am facing is the fact that proto copies around the
objects held in proto::terminals, whenever they have to go through a
generator. For example, I need to define operator(...) for the
expression returned by Program(). For that, I put it in a domain,
whose generator wraps the expression in a wrapper with operator(...),
but during that process, the objects held at terminals get copied. So
there is a new object created for each occurrence of a variable in the
expression, which screws up the evaluator. Any comments on trying to
hold the values "in situ"?

Manjunath