I'm not sure how this would be useful in Rust, but macros and tail calls are what allows one to (for example) write iterative loops in Scheme, which doesn't have a native loop syntax.
Maybe the same idea can be used in Rust where some constructs are easier to write in recursive form instead of a loop?
In any case, here's a silly example of a `for-loop` macro in Scheme using a tail call:
(define-syntax for-loop
(syntax-rules ()
((for-loop var start end body ...)
(letrec ((loop (lambda (var)
(unless (>= var end)
body ...
(loop (+ var 1)))))) ; <-- tail call
(loop start)))))
And here's how you'd use it to print the numbers 0 to 9:
(for-loop i 0 10
(display i)
(newline))
This macro expands to a function that calls itself to loop. Since Scheme is guaranteed to have proper tail calls, the calls are guaranteed to not blow the stack.
(Note that you'll probably never see a `letrec` used like this: people would use a named `let`, which is syntax sugar for that exact usage of `letrec`. I wrote it the `letrec` way to make the function explicit).
Maybe the same idea can be used in Rust where some constructs are easier to write in recursive form instead of a loop?
In any case, here's a silly example of a `for-loop` macro in Scheme using a tail call:
And here's how you'd use it to print the numbers 0 to 9: This macro expands to a function that calls itself to loop. Since Scheme is guaranteed to have proper tail calls, the calls are guaranteed to not blow the stack.(Note that you'll probably never see a `letrec` used like this: people would use a named `let`, which is syntax sugar for that exact usage of `letrec`. I wrote it the `letrec` way to make the function explicit).