Hi everybody,
thinking about array expressions, I have stumbled over an interesting
challenge for which I still have no idea:
Consider the mathematical sum notation:
\sum_i a_i*b_i
here, the variable i is defined only at the scope inside the expression.
A analogous D syntax could be something like
sum!(i)(a[i]*b[i])
where sum would have to be some kind of template that takes i as a name
parameter and then defines it as variable inside the scope of the second
expression.
(Of course, the scalar product is trivial enough to do it in a zillion
of other ways, but for more complex sum expressions with potentially
more than one variable, this would really be neat to have in an array
library.)
Does anyone have an idea how this could be realized in D? Allowing a
template to define additional symbols only for the scope of its
arguments? Is it possible at all with the current language definion?
Does anyone have an idea for an elegant language extension to allows
this? It would mean taking lazy evaluation even one step further, all
the way to a lazy symbol binding. Seems straighforward enough to me to
implement in a compiler. Just the question how exactly to define the
semantics.
Greetings,
Norbert
