Perl 6 modulinos are even easier

Perl 6 has this wonderful thing called MAIN which is a built-in modulino thingy.

In my excellent number hobby (which I started writing about in Mastering Perl even after I switched to C), I’ve been converting some bits to Perl 6 just for giggles. There’s a small Perl 5 module I wrote to get the number of CPUs I rewrote in Perl 6. It’s not sophisticated or surprising. It’s actually quite banal in function; merely dispatch to some method that knows what to do on the platforms I care about. And, be a modulino.

module CpuCount {
	sub run () is export {
		say get_cpu_count();

	sub get_cpu_count () is export {
		state $dispatch = {
			freebsd  => &_freebsd,
			_default => &_posix,

		my $key = $dispatch.{ $* }:exists ?? $* !! '_default';

		$dispatch.{ $key }.();

	sub _freebsd () { _get_conf( 'NPROCESSORS_ONLN' ) }

	sub _posix ()   { _get_conf( '_NPROCESSORS_ONLN' ) }

	sub _get_conf ( $key ) {
		state $command = '/usr/bin/getconf';

		unless $key ~~ m/ ^^ <[_A..Z0..9]>+ $$ / {
			warn "Key $key doesn't look acceptable";
		qq:x{$command $key 2>/dev/null}.chomp;

sub MAIN {
	import CpuCount;

First, MAIN. Perl 6 calls that if the file is the top-level thingy rather than something that’s loaded by something else. No more caller tricks. It’s even better though. Although I don’t need it here, if I give MAIN a signature, it does some argument handling automatically. And, lexical imports!

Back to the top of the program, I can create a module, similar to Perl 5’s package BLOCK syntax. I really like that. I get export handling without inheritance (that I can see, at least) by marking what is eligible with is export.

Inside get_cpu_count, I use the $*DISTRO special variable to find out what system I’m on. That’s an object with various parts I can access.

In the dispatch table, I get a reference to a subroutine by using the & in front of it. That messed me up for a bit, but I think I like that.

In _get_conf, I have a regex. That’s changed quite a bit with double typing. The ^^ and $$ are anchors, whitespace is insignificant by default, and character classes are much fancier. Those are put in <[ ... ]> because you can do set operations on the things in the square brackets. Very fancy, but there’s more typing. I also have to use .. to make a range of characters. Disk drives are cheap, so let’s use up those bytes!

I love string objects. I call the external command and can chomp it right away. And, chomp returns the modified string like God always wanted.

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