Add an HTML output module

Usage:
my $html = Grammar::Highlighter.new(:formatter(Grammar::Highlighter::HTML.new));
say $parser.parse(q:heredoc/INPUT/, :actions($html)ast.Str;

lib/Grammar/Highlighter/HTML.pm

@@ -0,0 +1,12 @@
+class Grammar::Highlighter::HTML;
+
+use Term::ANSIColor;
+
+my @colors = < aqua blue fuchsia gray green lime maroon navy olive purple red silver teal white yellow >;
+
+method colored(Str $code, Int $color) {
+    return qq!<span style="color: {@colors[$color % @colors.elems]};">{$code}</span>!;
+}
+
+# vim: ft=perl6
+

t/highlight.t

@@ -2,6 +2,7 @@ use Test;
 
 use Grammar::Highlighter;
 use Grammar::Highlighter::Terminal;
+use Grammar::Highlighter::HTML;
 
 grammar Foo {
     rule TOP {
@@ -26,9 +27,9 @@ grammar Foo {
 }
 
 my $parser = Foo.new;
-my $highlighter = Grammar::Highlighter.new(:formatter(Grammar::Highlighter::Terminal.new));
+my $terminal = Grammar::Highlighter.new(:formatter(Grammar::Highlighter::Terminal.new));
 
-is($parser.parse(q:heredoc/INPUT/, :actions($highlighter)).ast.Str, qq:heredoc/OUTPUT/.chomp);
+is($parser.parse(q:heredoc/INPUT/, :actions($terminal)).ast.Str, qq:heredoc/OUTPUT/.chomp);
     Foo Baz;
     Foo Baz;
     Bar Baz;
@@ -39,6 +40,19 @@ is($parser.parse(q:heredoc/INPUT/, :actions($highlighter)).ast.Str, qq:heredoc/O
     \x[1b][0m\x[1b][0m
     OUTPUT
 
+my $html = Grammar::Highlighter.new(:formatter(Grammar::Highlighter::HTML.new));
+
+is($parser.parse(q:heredoc/INPUT/, :actions($html)).ast.Str, q:heredoc/OUTPUT/.chomp);
+    Foo Baz;
+    Foo Baz;
+    Bar Baz;
+    INPUT
+    <span style="color: green;"><span style="color: fuchsia;"><span style="color: blue;">Foo <span style="color: aqua;">Baz</span></span>;
+    </span><span style="color: fuchsia;"><span style="color: blue;">Foo <span style="color: aqua;">Baz</span></span>;
+    </span><span style="color: fuchsia;"><span style="color: gray;">Bar <span style="color: aqua;">Baz</span></span>;
+    </span></span>
+    OUTPUT
+
 done;
 
 # vim: ft=perl6