I've been looking at the various ways of constructing lazy lists in Perl 6 and I would like to collect all of the concise ways of describing the Fibonacci sequence.
I will start this off with the three from masak's journal:
my @fibs := (0, 1, -> $a, $b { $a + $b } ... *);
my @fibs := (0, 1, { $^a + $^b } ... *);
my @fibs := (0, 1, *+* ... *);
I was thinking something like this would also work, but I think I have the syntax wrong:
my @fibs := (0, 1, (@fibs Z+ @fibs[1..*]));
Something there is eager (the slice?) and causes Rakudo to enter an infinite loop. It's a translation of the Haskell definition:
fibs = 0 : 1 : zipWith (+) fibs (tail fibs)
Update:
Seems like the problem with the zipWith example is the @fibs[1..*] slice. if tail is defined as sub tail (@x) {my $i = 1; {@x[$i++]}...*} then it works properly. I would be interested to know why the slice isn't lazy from anyone familiar with Rakudo's internals.
Another nice one is:
my @fibs := (0, [\+] 1, @fibs);