Transparancy

[Florian Weimer]

* Pavel Minaev:

> Indeed, can you give an example of a popular language which 1) has
> explicit "return", 2) has lambdas, and either 3) does not allow for
> "return" in a lambda, or 4) allows for it, but only in the meaning of
> non-local return?

Perl:

sub foo (@) {
    map {return} @_;
    print "map did not return non-locally\n";
}
print "calling foo\n";
foo;
print "calling foo\n";
foo 1;

Anonymous subs have proper returns, though.  I can ask around if this
is considered good language design.

(I think the consensus with regard to Perl's non-closing behavior of
named nested subprograms is that it's not a good idea at all.)

By the way, all Perl subs have non-local break/continue (which are
called last/next in Perl, in both local and non-local cases):

sub my_break {
    last;
}
sub foo {
    while (1) {
    print "foo\n";
    my_break;
    }
}
foo;

However, this coding style is discouraged, and the interpreter will
print a warning.

I think Common Lisp has got non-local returns within lexical scope on
downward closures (but Common Lisp was not conceived as a safe
language, so the trade-offs are quite different).  Obviously, FORTH
has got some unsafe construct for that purpose, too.  I also remember
using something else which had a similar "return from" mechanism, but
I don't recall which language that was (it certainly wasn't something
I would consider popular, perhaps HP-48 User RPL or something like
that).

-- 
Florian Weimer                <fweimer at bfk.de>
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