dynamic roles for grammars

dynamic-role.p6

use v6;

grammar G {
 proto token TOP { * };
 token TOP:sym<a> { 'a' };
};

class GA {
 method TOP { say "TOP"; };
 method TOP:sym<a> ($/) { say 'a' };
};


sub create ($name, &mtd) {
  my $foo = eval "
  anon role Add-to-grammar \{
    token TOP:sym<$name> \{ '$name' \};
  \};
";

  my $bar = eval "
  anon role add-to-actions \{
   method TOP:sym<$name> (\$/) \{ &mtd($/) \};
  \};
";

  return $foo, $bar;
};

my ($foo, $bar) = create 'b', { say 'b' };

(G but $foo).parse: 'a', :actions(GA.new but $bar);
(G but $foo).parse: 'b', :actions(GA.new but $bar);