Can Rust support non-local return?

[cuviper]

@CAD97

(The equivalent in Rust would be an unbound input lifetime, which makes storing the closure to be called later a borrow error.)

It wouldn't be terrible to represent this as a lifetime bound to the lexical control flow it affects, as if it borrowed a local in that scope. But I think we would also need some explicit function trait for this, so existing code that takes Fn / FnMut / FnOnce doesn't have to worry about non-local control flow.

Here's an older thread on TCP closures:

An idea for TCP closures and rust's effect system

The idea is to introduce a new kind: effects. They are typed, polymorphic generic parameters. Used as fn: fn<T,effect A<T>> effectful() they can depend on a datatype that they can later return. Syntax of actually using them is following: return 'A val; Calling such a function is done like: let val = 'lab { effectful<'lab>(); 1usize } Here the 'lab label is used to denote a block whose type is being used as a type for effect. So the effectful function can return 'A 0; and make the bl…