Re: ALTER, ASSIGN and labels-as-values

Anton Ertl wrote:

EricP <ThatWouldBeTelling@thevillage.com> writes:

Don't forget Fortran's alternate returns, indicated by a * in the arg
list.
A caller subroutine passes *labels in the args list, and callee decides
which *label-arg it wants to return to in the RETURN statement constant
expression. (This is not ambiguous because in Fortran function return
values are done by assignment to the function name, not the return
statement expression.)
>
call Foo (*100, *200)
...
100
...
200
...
end
>
subroutine Foo (*, *)
...
return 1       ! Return to callers first * label arg
...
return 2       ! Return to callers second * label arg
...
end

Interesting.  Rudimentary explicit continuation-passing style at the
dawn of programming languages.  Of course, these days it would mean
that you better not use the common call and return instructions,
because the branch prediction for the return would be wrong if return
1 or return 2 would be used.  But using plain jump for the call and
indirect jumps for the returns should be efficient on modern CPUs.

That is why the subroutine returns a value and the return point implements the switch (control transfer to proper label.
{You DO NOT return to the label, you return normally and then go to the proper label.}

- anton