Yesterday, for the last day of The Perl Conference (formerly known as YAPC) in Glasgow, Scotland, Curtis "Ovid" Poe delivered a very inspiring keynote address on the future of Perl.

Ovid's idea was to imagine where Perl 5 would stand in ten years from now.

These are some of the things Perl would have in 10 years in Ovid's vision:

• (Non experimental) Function signatures along with a gradual typing system;
• A simple core OO system (see http://blogs.perl.org/users/ovid/2018/07/the-future-of-perl-5.html)
• An inline keyword to support functions in-lining to boost performance while not repeating oneself;

As an example for the first point above, consider the following subroutine:

sub fibonacci {
    my $n = shift;
    return 1 if $n == 1 or $n == 0;
    return fibonacci($n-1) + fibonacci($n-2);
}
[download]

This subroutine should work correctly if the subroutine is called with a positive integer, but a number of things could go wrong: what will happen if no parameter is passed to the subroutine? or if the parameter is a negative integer, say -3? or if the parameter is a positive number but not an integer, e.g. 3.14? or if the parameter is not a number but a string? (Note that there would also be a problem with a large integer, but that's a different story.)

For the above subroutine to be correct, you would need to add probably half a dozen boiler plate code lines to guard against invalid input, for example maybe something like this:

sub fibonacci {
    die "..." unless defined $_[0];
    my $n = shift;
    die "..." unless is_a_number($n); # the is_a_number function is to
+ be defined
    die "..." if $n < 0;
    die "..." if $n != int $n;
    # ...
}
[download]

With (non experimental) function signatures and proper typing, all you would need might just boil down to something like:

sub fibonacci (PositiveInt $n) {
    return 1 if $n <= 1;
    return fibonacci($n-1) + fibonacci($n-2);
}
[download]

I think this would look quite cleaner.

I hope the video of Ovid's talk will on-line soon.

Comments are welcome.

Update (Aug 23): ovid created a new meditation explaining his views with some details here: Recap: The Future of Perl 5.

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