On Monday, 25 May 2015 at 23:40:46 UTC, Vlad Levenfeld wrote:
I don't mean nested arrays, I mean an equivalent recursive
definition for the sake of exposing a "natural" traversal
strategy, which you get if your object admits the notion of a
pointed element and of proper disjoint subobjects. For example:
T[0..$] = {T[0], T[1..$]}
T[0..$, 0..$]
= {T[0, 0..$], T[1..$, 0..$]}
= {{T[0, 0], T[0, 1..$]}, T[1..$, 0..$]}
And so on. The second definition is just lexicographic
traversal expressed in recursive language.
If there were a way to write an adaptor to deduce such a
recursive definition and then present it as an input range, you
could have a uniform syntax for iterating over
differently-shaped data structures.
The problem that I run into is presenting this as an input
range for foreach. "front" obviously refers to the pointed
element, but "popFront" typically returns void, not a smaller
instance of the object - which means things like trees and
multidim arrays need to eschew "front/popFront/empty" in favor
of something like "head/tails[]" (with tails[].empty == true
being the termination condition), but this isn't a viable
solution for foreach loops.
I'm writing this in a bit of a hurry so I might be missing
something essential but this is more or less the conclusion
that I've reached after spending the last few months thinking
about the problem. Fresh ideas are very welcome.
The system of disjoint sets and D-ranges. Sounds great! I think
about what ideas can be offered. The idea is very good!
