Re: [Boost-users] [proto] generation of adaptive precision floating-point geometric predicates

Hi Kim, Thanks very much for your response and the sample code.

How about transform the expression a+b to sum_approx(a,b)+sum_diff(a,b) instead to fusion::cons > ? The advantage of this approach is that you still get an ast where childs are held in terminal (instead in cons).

You are correct that the elements being generated will represent terms to be summed together. My rationale for choosing to represent them as a sequence rather than a tree was to make it easier to modify the order in which the summation is performed. Namely, I plan to sort the terms according to their expected magnitude so that I can add them up until the magnitude of the result exceeds the maximum possible magnitude of the error (hence guaranteeing that the sign is correct). The value of any remaining terms should never actually be computed. Having said that, if it makes life easier to generate an AST with an n-ary "sum" function rather than a sequence or a deep tree of binary "plus" nodes, then that would be fine too. The final tree should then consist of a single "sum" node with a long list of terms.

I dont see the meaning behind this step. If you use proto::_make_function you create a child in the ast, but you put this child in a fusion::cons.

Yes, exactly. The resulting sequence should consist of AST nodes that can be evaluated one by one until the stop condition is reached.

Are you sure that you want to get a sequence of expression instead an ast. In case you really want to get a sequence you can use proto::tag::comma to separate your child.

Yes, I think so -- but that doesn't exclude the possibility that I'm going about this in completely the wrong way :)

Here is a toy project. Hth.

Thanks again for taking the time to respond. andrew