Exec-tree-example.pl

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Example of nodal reduction in Perl.

#!/usr/bin/perl -w
use strict;

# First, we set up three test threads each of three sequencial functions
# - Each function simply prints its name and returns a reference to the next in its thread
# - In reality the functions would be acting on their local environment
#   (in PERL the local environment is in the global $cwd hashRef)
# - and what's returned can be not only a function, but another hashRef or void if its finished

our ($A,$B,$C, $P,$Q,$R, $X,$Y,$Z);
$A = sub {print "A"; return $B;};
$B = sub {print "B"; return $C;};
$C = sub {print "C"; return $A;};

$P = sub {print "P"; return $Q;};
$Q = sub {print "Q"; return $R;};
$R = sub {print "R"; return $P;};

$X = sub {print "X"; return $Y;};
$Y = sub {print "Y"; return $Z;};
$Z = sub {print "Z"; return $X;};

# The execution tree is set up with the root containing thread-ABC
#   and another node which contains threads PQR & XYZ
# - So PQR and XYZ execute in parallel and as a whole they execute in parallel with ABC

my $someNode = {queue => [$P,$X]};
my $root = {queue => [$A,$someNode]};
our $cwd;  # In PERL the functions act on their local environment which is the $cwd hashRef

while (1) {
	$cwd = $root;
	for (my $i = 1; $i == 1;) {
		my $queue = $$cwd{'queue'};
		if ($#$queue >= 0) {
			my $todo = shift @$queue;
			push @$queue, $_ if $_ = (ref $todo eq 'CODE') ? ($i = &$todo) : ($cwd = $todo);
			}
		else	{$i = 0}
		}
	}