experiment showing how iterators can (almost) be implemented with a library solution

[timotheecour]

support material for nim-lang/RFCs#272

would fix these long standing issues with closure iterators:

• closure iterators can't be used in VM
  Closure iterators are not supported by VM #15818
• closure iterators can't be used in js
  Problem with closure iterators in js target #4695
• closure iterators can't be recursive
  https://forum.nim-lang.org/t/7020#44149
• defer/exceptions don't work in closure iterators:
  Closure iterators do not respect try/finally or defer #15501
  Defer in iterators is only guaranteed if the iterator runs to completion #11815
• Closure iterators can leak resources and there is no easy way to prevent it · Issue #13289 · nim-lang/Nim Closure iterators can leak resources and there is no easy way to prevent it #13289

links

• Closure iterators do not respect try/finally or defer #15501 (comment)
• can iterators be implemented as a library solution / syntax sugar over regular procs? RFCs#272

[Araq]

Why is this a pull request? This is not a pull request. And the RFC is refers to is not an RFC, it's a question. A valid, interesting question with known answers: Yes it can.

[Araq]

Reopening for the sake of it, but it's still not clear to me why:

• This cannot at least start as a fusion module, if it cannot be a Nimble package.
• These ideas cannot ported into the compiler so that closure iterators work better than before.

[dom96]

This cannot at least start as a fusion module, if it cannot be a Nimble package.

This. You're just creating noise by creating this as a PR.

[stale]

This pull request has been automatically marked as stale because it has not had recent activity. If you think it is still a valid PR, please rebase it on the latest devel; otherwise it will be closed. Thank you for your contributions.

[ringabout]

On the other hand javascipt or VM can support closures => #23493