Re^2: fibonacci numbers using subroutine?

[moritz]

Just to show off, here's a Perl 6 solution:

sub MAIN($limit as Int) {
    say (0, 1, *+* ... *)[$limit];
}

Which you call as

perl6 fib.pl 8

To obtain the 8th fibonacci number.

As an explanation, MAIN takes its arguments from the command line, and is run automatically at startup. as Int converts the command line argument (which is a string) to an integer (this is not sctrictly necessary). 0, 1, *+* ... * is a lazy, infinite list starting with 0 and 1, and then is built by summing the two previous elements. [$limit] takes the $limit's element of that list, with a zero-based index. (Which is why the fibonacci sequence starts with 0, 1 instead of 1, 1 in that program).

[TimToady]

In practice, though, if you're going to reuse a series in your Perl 6 program, you'll want to memoize the series by binding the series to an array, like this:

my @fib := (0,1, *+* ... *);
say @fib[8];
say @fib[9]; # doesn't recalculate fib(8)

Both lists and arrays can be lazily infinite in Perl 6; the only real difference is whether the values are kept in an indexable form as they are generated. Note also that the memoization naturally uses an array rather than a hash in this case, which saves memory over those memoization techniques that must assume a hash for generality.

[JavaFan]

Wait. Perl6 doesn't have OEIS() as a primitive? I can't just do OEIS(45)[8].say?

[moritz]

No, but we do have a module system that allows you to write that.

See a small guide for module authors if you feel like contributing - it would certainly be appreciated.

[JavaFan]

Well, I can easily write such a module in Perl. For now, I've no interest in Perl6, so I'll spend my time on Perl instead.