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From: noitalmost <noitalmost@cox.net>
Newsgroups: comp.compilers
Subject: Re: Is multi-level function return possible?
Date: Sat, 15 Mar 2014 12:21:52 -0400
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On Tuesday, March 11, 2014 09:04:57 AM Anton Ertl wrote:
> Yes, in Pascal you can goto a label that is in a containing procedure
> or function, even across several levels.  That is a very rarely used
> feature of the language, and Wirth removed it (along with goto) from
> his later languages.

I had to go look that up. Yep, it's there in the ISO standard, as one of the
uses of goto. This is kind of like what I had in mind. I was thinking of a
prettier syntax, though:
procedure f() :
  procedure g() int :
    procedure h() :
      return from g 3;
    end h;

    h();
    nope();  # doesn't get called
  end g;

  x : int;
  x := g();
  print x;  # prints 3
end p;

The syntax meshes nice with my break stmt:
while {outer} x < 10 :
  loop :
    break from outer;
  end;
end;

It's a lot more restrictive than exeptions, and I'm not sure if has any use,
but it looks nice :)
The only potential use that comes to mind is:
procedure p() :
  procedure r() :
    cond : bool;  # some condition
    break from r if cond;
    r();
  end r;
end f;

f();

The break would cause a quick exit by blowing away all the intervening stack
frames from the recursive calls to r.

I'm assuming I can implement this without too much trouble, since it could be
done in Pascal. Is that true?
[I would think so.  See the next message. -John]