gistfile1.txt

─> cat test
grammar Foo {
    token TOP    { <bottom> }
    token bottom {   <?>    }
}

class Foo::Actions {
    method TOP($/) {
        my $grmr := Metamodel::GrammarHOW.new_type(name => 'BNFGrammar');
        $grmr.^add_method('TOP', token { <foo> });
        $grmr.^add_method('foo', $<bottom>.ast);
        $grmr.^compose;
        {
            my $/;
            say $grmr.new.parse('bar');
        }
    }

    method bottom($/) {
        make token { "bar" }
    }
}

Foo.new.parse('', :actions(Foo::Actions.new))

─> perl6 test
｢bar｣
 foo => ｢bar｣

─> diff -uN test test.fail 
--- test	2015-04-19 16:13:23.475552957 +0200
+++ test.fail	2015-04-19 16:13:47.147928163 +0200
@@ -7,7 +7,7 @@
     method TOP($/) {
         my $grmr := Metamodel::GrammarHOW.new_type(name => 'BNFGrammar');
         $grmr.^add_method('TOP', token { <foo> });
-        $grmr.^add_method('foo', $<bottom>.ast);
+        $grmr.^add_method('foo', $<bottom>.ast[0]);
         $grmr.^compose;
         {
             my $/;
@@ -16,7 +16,7 @@
     }
 
     method bottom($/) {
-        make token { "bar" }
+        make [token { "bar" }]
     }
 }
 
─> perl6 test.fail 
Cannot find method 'postcircumfix:<( )>'
  in regex  at test.fail:9
  in method parse at src/gen/m-CORE.setting:16692
  in method TOP at test.fail:14
  in regex TOP at test.fail:2
  in method parse at src/gen/m-CORE.setting:16692
  in block <unit> at test.fail:23