Re: Isn't Perl5 ready for C<my sub>?

sub invert {
    my ($n, $p)=@_;
    # Trusting $p to be a prime...
    local *expp = sub {
        my ($n, $m)=@_;
        return 1 unless $m;
        ($m%2 ? $n : 1) * expp($n, $m >> 1)**2 % $p;
    };
    expp($n, $p-2);
}
[download]

(With all the caveats of local and symboltable hacking, of course.)

-- Randal L. Schwartz, Perl hacker
Be sure to read my standard disclaimer if this is a reply.

Comment on Re: Isn't Perl5 ready for C<my sub>? Download Code

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Re^2: Isn't Perl5 ready for C<my sub>? by friedo (Prior) on Sep 07, 2005 at 16:48 UTC
(With all the caveats of local and symboltable hacking, of course.) The main problem I see with this approach is that it doesn't behave the way we would expect a true lexical sub too. For example, I would expect the following to work: `sub foo { my sub bar { print "42\n"; } return sub { bar() }; } my $s = foo(); $s->();` [download] Of course that won't work with the `local` trick since you can't have a lexical closure over a locally modified symbol table (as far as I know.) But it would work fine if you used `my $bar = sub { print "42\n" }`. I suppose a source filter to convert `my sub bar { }` to `my $bar = sub { }` would do the trick, but then you'd have to scan the rest of the block to change `bar` to `$bar->()`. Sounds like a real PITA.	[reply] [d/l] [select]
Re^2: Isn't Perl5 ready for C<my sub>? by blazar (Canon) on Sep 07, 2005 at 15:26 UTC
(With all the caveats of local and symboltable hacking, of course.) Indeed. In fact this is a hack. Granted, a nice hack, but as I wrote, not that it is impossible to work around the lack of lexically scoped named subs, it's possible and even easy. We still simply lack them and I would feel comfortable having them instead. I would just be interested to know whether there's some major technical difficulty in this sense...	[reply]


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