fjwhittle: week 3, part 1, perl 6

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+#!/usr/bin/env perl6
+
+use v6;
+
+subset Count of Int where * > 0;
+
+#| Script to generate 5-smooth numbers
+unit sub MAIN(
+  Count :n(:$count) = 20, #= How many 5-smooth numbers to generate.
+  *@print #= specific indices to show.
+);
+
+# Use a lazy list to generate 5-smooth numbers
+my @smooth5 = lazy gather {
+  take 1; # 1 is the first
+
+  # Initialize some iteration counters.
+  my ($i2, $i3, $i5) = 0 xx 3;
+
+  # I wanted to use actualy Iterators here, but couldn't figure out how to not
+  # pull elements that didn't exist yet.
+
+  # Generate the next number for each divisor
+  my $n2 = @smooth5[$i2++] * 2;
+  my $n3 = @smooth5[$i3++] * 3;
+  my $n5 = @smooth5[$i5++] * 5;
+
+  # Just keep generating.  Does the list become sparse?  I don't know!
+  loop {
+    # Minimum of the latest iterations
+    my $n = ($n2, $n3, $n5).min;
+    take $n;
+
+    # Advance the generators that matched.
+    $n2 == $n and $n2 = @smooth5[$i2++] * 2;
+    $n3 == $n and $n3 = @smooth5[$i3++] * 3;
+    $n5 == $n and $n5 = @smooth5[$i5++] * 5;
+  }
+}
+
+@smooth5.[^$count].say;
+
+for @print -> $n {
+  ($n.fmt('%7d') ~ ': ' ~ @smooth5[$n-1]).say;
+}