On Thursday, September 13, 2018 at 4:00:28 PM UTC-6, Jonathan Amsterdam
wrote:
>
> What's the meaning of this code?
>
> func main() {
> f := g()
> f()
> }
>
> func g() func() {
> Top:
> return func() { returnfrom Top, nil}
> }
>
It means you're an evil programmer. 😜
My thinking is that returning from a no-longer-accessible continuation
should simply be a no-op. Stepping through your example, f := g() assigns
func()
{ returnfrom Top, nil } to f. At this point the call stack associated with
g() is no longer live. f() executes, turning into returnfrom Top, nil.
The returnfrom causes the inner function to return immediately and
instructs g() to return nil. But because the continuation corresponding to
the call to g that returned the inner function no longer exists, there's no
place to send that nil, and nothing happens.
I believe this is a simpler and more Go-like semantics than, say, Scheme's
call/cc, which *does* execute the f := g() statement twice:
(define (main)
(let ((f (g)))
;(printf "Calling f = ~s~n" f)
(f)))
(define (g)
(call/cc
(lambda (Top)
(lambda ()
(Top '())))))
(Uncomment the printf to see the double execution. Weird, huh?)
Thanks for the challenge,
— Scott
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