Perlでたらいまわし関数

• See: 竹内関数 - Wikipedia

tarai.pl

#!/usr/bin/env perl
use strict;
use warnings;

my $count = 0;

sub tarai {
    my ( $x, $y, $z ) = @_;

    $count++;
    warn "$count: tarai($x, $y, $z)\n";

    if ( $x <= $y ) {
        return $y;
    }
    else {
        return tarai(
            tarai( $x - 1, $y, $z ),
            tarai( $y - 1, $z, $x ),
            tarai( $z - 1, $x, $y )
        );
    }
}

my @args = ( @ARGV >= 3 ) ? @ARGV : ( 10, 5, 0 );

print tarai(@args), "\n";