An `async {}` block is not evaluated, but converted into a generator/state machine that lives on the stack, and that has to be advanced by calling a poll method. You can move it to the heap , but that does not happen automatically.
Sharing of values is obviously much more awkward due to mutability and no automatic cloning though.
But to be clear, anyone with the username the_duke is probably really cool, and you clearly know your stuff as well as having style, so count me as a fan.
But not so much in the conditional branch sense of the phrase “control flow”.
More like, I’ve got a bunch of references and one of them is a reference to a function I might evaluate, damn, I need that reference and the transitive closure of everything it knows about, all of which are probably on the heap.
A space leak, much like any memory leak is when you or the compiler or the runtime or whoever misplaces such reference.
GHC having a closure in scope in no way immediately means there is a space leak. Plenty of Haskell code that compiles to thunks will run all day in an amortized fixed-size heap.
Much like Erlang, which is what Joe Armstrong had designed before he said the thing about jungles you’ve quoted.
And it is in no way difficult or even really rare to drop an Arc in a table and leak all over the place.
Rust has all the same computer science problems as anything else. Full stop.
Now GHC does stack allocate, but it’s hard to count on without really aggressive hinting.