Mandelbrot Set algorithm in Perl6

Generates the Mandelbrot Set fractal using Perl 6. To be submitted to "The Computer Language Benchmarks Game".

categories/shootout/mandelbrot.p6

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+use v6;
+
+=begin pod
+
+=TITLE Generates the Mandelbrot Set fractal
+
+=AUTHOR Rodrigo Siqueira (@rsiqueira)
+
+To be submitted to "The Computer Language Benchmarks Game", to test Perl6 speed / performance 
+in comparison with other programming languages.
+
+L<https://benchmarksgame.alioth.debian.org/u32q/mandelbrot-description.html>
+L<http://benchmarksgame.alioth.debian.org/u32/performance.php?test=mandelbrot>
+L<http://benchmarksgame.alioth.debian.org/u64/performance.php?test=mandelbrot>
+
+USAGE: perl6 mandelbrot.p6 200 > image.pbm
+
+=end pod
+
+
+
+constant $MAXITER = 50;
+constant $xmin = -1.5;
+constant $ymin = -1.0;
+
+my $w = (@*ARGS[0] || 200);
+my $h = $w;
+
+my Rat $invN = 2/$w;
+
+print "P4\n$w $h\n"; # PBM image header
+
+my Int $bit_num = 0;
+
+my Int $is_set=1;
+
+my Int $byte = 0;
+
+for (0..$h-1) -> $y {
+
+  my Rat $y_coord = $y * $invN + $ymin;
+
+  for 0..$w-1 -> $x {
+
+    my Rat $x_coord = $x * $invN + $xmin;
+
+    my Complex $C = $x_coord + $y_coord\i;
+
+    my Complex $z=0+0i;
+
+    for (0..$MAXITER) { # Iterate
+
+      $z = $z * $z + $C;
+
+      if ($z.abs > 4) { # Outer area of the Mandelbrot Set
+        $is_set = 0;
+        last;
+      }
+
+    }
+
+#    if ($is_set) { # Inner area of the Mandelbrot Set
+#      print "o";
+#    } else {       # Outer area
+#      print ".";
+#    }
+
+    $bit_num++;
+
+    $byte = $byte +< 1;
+    if ($is_set) {
+      $byte = $byte +| 1;
+    }
+
+    if ($bit_num == 8) {
+
+      $bit_num = 0;
+      my $buf = Buf.new( $byte );
+      $*OUT.write($buf);
+      $byte = 0;
+
+    } elsif ($x == $w-1) { # (8 - $w%8) bits to fill out the last byte in the row
+
+      $byte = $byte +< (8 - $w%8);
+      my $buf = Buf.new( $byte );
+      $*OUT.write($buf);
+      $byte = 0;
+      $bit_num = 0;
+    }
+
+    $is_set=1;
+
+  } # Next x
+
+#  print "\n";
+
+} # Next y