I can see at least two issues. I'm sure you're aware of these, but: - Rust closures don't really support recursion, at least without serious hacks. - Rust cl

I can see at least two issues. I'm sure you're aware of these, but: - Rust closures don't really support recursion, at least without serious hacks. - Rust closures borrow the variables they reference as soon as the closure is created; you can never write to those variables again as long as the closure is alive, and if the closure mutates the variable (resulting in a mutable borrow), you can't read from them either, outside the closure itself. The latter isn't as a big a deal for some other use cases for closures, but if you want to use them to emulate nested functions, you're probably creating the closure at the beginning of the outer function and keeping it in scope for the whole function; this means that what you can do with mutable variables is severely limited. Both issues could be worked around if the mechanical translator liberally sprinkled the code with Cell/RefCell – which would also be necessary to deal with pointers in the source language. But the result would be highly unidiomatic and verbose Rust code. (In any case, I'm not sure I'd have recommended Rust to OP as they claim to put a high priority on fast compile times, but that's a separate issue.)