[Feature Request] Add support for recursive @parameter closures

[soraros]

Bug description

As title.

Steps to reproduce

fn fib(n: Int) -> Int:
  @parameter
  fn fib_tail(n: Int, a: Int, b: Int) -> Int:
    if n < 1:
      return 0
    elif n == 1:
      return b
    return fib_tail(n - 1, b, a + b)
  return fib_tail(n, 0, 1)

System information

Mojo 2024.8.2916 (1e9c68e6) on Docker, Intel Mac

[bpr]

mojo/docs/roadmap.md

Line 599 in 17662e3

### Nested functions cannot be recursive

[soraros]

@bpr Ah, right. Let me make this a feature request for @parameter closures.

Actually, I'm not so sure now. I think the roadmap was written before the new closure model, so it was taking about @parameter fib_tail not fib_tail which was in my original bug report. At least the compiler should give proper error message if @parameter's missing.