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cyocum (7706)

cyocum
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http://cyocum.blogspot.com/

An American post-graduate student living in Scotland.

Journal of cyocum (7706)

Sunday December 07, 2008
09:45 AM

Perl6 Lives!

[ #38044 ]

Ok, this has probably been done by someone else who is better than me elsewhere but I just wanted to show off some of Perl6 and the fact that you can code in Perl6 and that is just damn cool.

use v6;

say factorial(10);

sub factorial(Int $int) {
  my $fac_times = sub(Int $n, Int $acc) {
    if($n == 0) {
      return $acc;
    }

    return $fac_times($n - 1, $acc * $n);
  };

  die "Wrong argument!!" if $int < 0;
  return $fac_times($int, 1);
}

What this code does is translate the code from the Wikipedia article on tail recursion from Scheme to Perl6 for the factorial function. It even runs pretty well on an unoptimized build of parrot+rakudo. Thank you Parrot/Perl6 People!

update: I added the die and removed the useless "else" in the inner sub.

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  • my $fac10 = [*] 1 .. 10;

    It isn’t even worth pulling out into a function.

    • Perl Golf still lives, I see. I had started playing around with subsets and had intended to update it with stuff like that but I will just say wow...that is really neat.

      • It’s not golf! That’s just bog-standard Perl 6. Hyper- and reduce operators are normal part of the repertoire and in fact one of the reasons I am looking forward to v6. They get rid of huge swathes of monkey code… as you just saw. Lots of things that would require loops, which really constitute nothing but accidental complexity, can be expressed by a single operator.

        • Like all good things, I hope Perl 6 will change my perception of programming.

        • This old APL/J and Prolog programmer agrees that Perl6 is my dream languoge, as it has hyper / reduce and grammars/structure-matching search, plus threads, though perhaps without the elegance of Hoare-Dijkstra parallel calculus as I originally envisaged (nor even the terseness of sh's & ).

          However, how will the simple [*] 1..$n work or fail when $n is large like 100 or 8.424000e+08 ? Does it magically transform to a generator and tail recursion under the covers, or does it do what it appears to say an

          --
          Bill
          # I had a sig when sigs were cool
          use Sig;