From @masak

From <http://use.perl.org/~JonathanWorthington/journal/39856>&#8203;:

] Added handling of the grammar package declarator back in. Now the
] "inherit from Grammar by default and not Any" stuff is just done by
] us having a metaclass for grammars - GrammarHOW - that subclasses
] the metaclass for classes - ClassHOW. It simply overrides the
] compose method (what we call when we're finished defining a package)
] and checks if there are any explicit parents, and if not adds Grammar
] as a parent, then delegates up to the superclass to do the rest of the work.

<masak> rakudo​: class A {}; grammar G is A { regex TOP { foo } }; G.parse("foo")
<p6eval> rakudo 90637b​: OUTPUT«Method 'parse' not found for invocant
of class '' [...]
<masak> I know, that's a bit of "doctor, it hurts when I do this"...
<moritz_> masak​: I'd say it's a bug. 'grammar' should add Grammar to
the list of its parents, unless one of the explicit parents is Grammar
already
<moritz_> at least I think that's what it should do.
<masak> oh, good.
* masak submits rakudobug
<moritz_> and I know where to fix it
<moritz_> src/metamodel/GrammarHow.pir around line 41
<jnthn> :-)
<jnthn> Yes, that's HOW.
<moritz_> if it were written in Perl 6, I'd say if
none(@​parents>>.isa(Grammar)) { $P0.add_parent(Grammar, $P0) }
<jnthn> It'll be written in NQP at some point.
<moritz_> jnthn​: how hard would it be to rewrite it now?
<jnthn> moritz_​: Probably quite easy.
<jnthn> Though a bit messy, since for now you'd still need pir​::foo I guess

From @cognominal

patch attached

From @cognominal

From 4bfe94e440eccb22490fe7b97064428b204e00f2 Mon Sep 17 00:00:00 2001
From: Stephane cognominal Payrard <cognominal@gmail.com>
Date: Sat, 21 Aug 2010 11:10:01 +0200
Subject: [PATCH] fixes #77322 : changed sub compose in GrammarHOW.pir so that grammars always inherit from Grammar

---
 src/metamodel/GrammarHOW.pir |   20 ++++++++++++++------
 1 files changed, 14 insertions(+), 6 deletions(-)

diff --git a/src/metamodel/GrammarHOW.pir b/src/metamodel/GrammarHOW.pir
index 6c36a64..c5b7110 100644
--- a/src/metamodel/GrammarHOW.pir
+++ b/src/metamodel/GrammarHOW.pir
@@ -26,20 +26,28 @@ Grammar by default.
 
 =item compose(meta)
 
-If there is no explicit parent, makes Grammar the default parent and then
+If none of the parents is a Grammar, add Grammar as a parent and then
 delegates to ClassHOW.
 
 =cut
 
 .sub 'compose' :method
     .param pmc obj
-    .local pmc parrotclass
+    .local pmc parrotclass, grammarclass
+    grammarclass = get_hll_global 'Grammar'
     parrotclass = getattribute self, 'parrotclass'
     $P0 = inspect parrotclass, 'parents'
-    if $P0 goto have_parents
-    $P0 = get_hll_global 'Grammar'
-    self.'add_parent'(obj, $P0)
-  have_parents:
+    unless $P0 goto add_grammar_as_parent
+    $P1 = iter $P0
+loop_on_parents:
+    unless $P1 goto add_grammar_as_parent
+    $P2 = shift $P1
+    $I0 = $P2.'isa'(grammarclass)
+    if $I0 goto loop_on_parents_done
+    goto loop_on_parents
+  add_grammar_as_parent:  
+    self.'add_parent'(obj, grammarclass)
+  loop_on_parents_done:
     $P0 = get_hll_global 'ClassHOW'
     $P0 = find_method $P0, 'compose'
     .tailcall $P0(self, obj)
-- 
1.7.0.3.291.g5e4f6

The RT System itself - Status changed from 'new' to 'open'

From @moritz

thanks, applied the patch, and added tests to S05-grammar/inheritance.t

@moritz - Status changed from 'open' to 'resolved'