Proto for Boost mailing list page: Re: [proto] Manipulating an expression tree

Subject: Re: [proto] Manipulating an expression tree
From: Karsten Ahnert (karsten.ahnert_at_[hidden])
Date: 2011-04-08 04:28:41

> (Please don't top-post. Rearranging...)

Hmm, I just used reply in my mail client. (Sorry for this double)

>> Another question is: can a node have a state. In my algorithm it would
>> be nice, if every proto::multiplies< > node stores some intermediate
>> values which are used during later evaluations of the tree.
>
> No. Intermediate expression nodes carry no run-time state in their
> nodes. They only carry compile-time information in the form of the tag.
> That's how a plus node is distinguished from a minus node, for instance.
>
> If you need to compute intermediate values, you can use a transform to
> build a parallel structure.

Do you mean to build an entire new tree, or just to replace some nodes?

In my current algorithm I use callable contexts to do the work. I think
this is more favorable since I have to evaluate the tree N times to obtain
the result. I think it would be nice to replace some nodes and customizing
the evaluation context, such that these nodes can be used to store the
intermediates.