Set up an array of hashes containing the current values and iteration counts then pass each hash in turn with a code reference to a routine to calculate the next iteration.
my $calculator = sub ($n is rw) {
$n == 1 ?? 1 !! $n %% 2 ?? $n div 2 !! $n * 3 + 1
}
sub next (%this, &get_next) {
return %this if %this.<value> == 1;
%this.<value> .= &get_next;
%this.<count>++;
%this;
}
my @hailstones = map { %(value => $_, count => 0) }, 1 .. 12;
while not all( map { $_.<value> }, @hailstones ) == 1 {
say [~] map { $_.<value>.fmt: '%4s' }, @hailstones;
@hailstones[$_] .= &next($calculator) for ^@hailstones;
}
say "\nCounts\n" ~ [~] map { $_.<count>.fmt: '%4s' }, @hailstones;