Joel Falcou wrote:
Eric Niebler a écrit :
A very simple example is a lambda library with placeholders. Imagine you wrote a transform that evaluated lambdas with arguments. When evaluating a lambda expression such as (_1 + _2) with the arguments (3,4), you might pass the arguments to the transform as a tuple in the Data parameter (a.k.a Visitor). Then, when the transform has recursed to a placeholder terminal, say _1, the result would be the 0th element in the Data tuple.
Doesn't this features make context obsolete ? I mean instead of using context to traverse the AST and performs evalmuations, oen can simply build a proper visitor and traverse the AST in a way simialr to a classic visitor pattern ?
Yes, in proto v4 contexts are not necessary. They can, in some circumstances, be easier to work with then transforms, so I don't plan to remove them. They may even be better at compile time.
I have reimplemented the Boost Lambda Library on top of proto using this technique. You can find it here:
I'll get a look. Seems alos that I missed the v4 branches. Is there large changes between this and the last proto zip that was available ont he vault ?
There are non-trivial changes, yes. Most significantly, the protocol for implementing custom transforms has changed. Also, a bunch of functions and types have been renamed as a result of review feedback.
Two other questions : - why does trasnform apply deep copy onto terminals ?
Not sure what you mean. Can you give an example?
- I'm currently using proto to implement some parallel programming library and I have to explain what I do with proto to people more used to the classic compilation/semantic vocabulary than to the proto idioms. in this context, is it correct to say that transforms are "semantic actions" applied onto the element of the AST ?
Absolutely. A proto transform *IS* a semantic action. -- Eric Niebler BoostPro Computing http://www.boostpro.com