Re: [boost] [proto] transform for flattening an expression - how?

From: Markus Werle (numerical.simulation_at_[hidden])
Date: 2008-03-20 08:50:59

Steven Watanabe <watanabesj <at> gmail.com> writes:

> If you want to iterate over all the terms in a transform use fold_tree.
> I don't see any benefit of flattening the expression, besides making things
> harder for proto :)

We are talking about a general purpose ET library here.
There are n-ary operators and function calls in the RealWorld.
So these _must_ be first class citizens in proto.

Having (a+b+c+d) represented has expr<sum, etc.> is crucial
for what I want to do with proto, namely compile-time
analytic differentiation in conjunction with expression 
simplification.

Looking at expressions as tree is only half of the truth
and I always found this was lovely (citing Todd V.), but not  
useful everywhere.

Eric took the correct path using the expr<op, typelist> idiom.
Lets not step behind that one.

Markus