# The average/starting dev in the team never needs to see
# this code, and thus doesn't need to learn anything about the
# meta-programming going on. Too much use of meta-programming
# in any complex codebase can lead to problems...
#  ... but also solutions.

role Foldable {
	method left-fold(&f) {
		self.reduce(&f) but Foldable
	}
	method parallel-map(&m) {
		self.hyper.map(&m) but Foldable
	}
	method push(*@a) {
		(self, @a) but Foldable
	}
}

# A CLI app that can be easily adapted to your
#   folding needs. If you know what you are doing,
#   they could easily be the same file.
sub MAIN() {
	my $fold-this = [1 .. 10] but Foldable;
	my sub adder($a, $b) {
		# anonymous state variable eases recursive type thinking
		$a + $b + $++
	}
	my $folded = $fold-this.parallel-map({ $_ + 1 }).left-fold(&adder);
	{
		use Test;
		ok { $folded == 101 }, "The adder works as expected";
		ok { $folded ~~ Foldable }, '$folded is ready to fold again';
		ok { $folded.push(1..5).left-fold(&adder) == 115 }, 'Add some more friends and fold again';
	}
}