Use 6.e Grammar class as default for grammar decalarations

Do it with EXPORTHOW and specialized HOW metaclass.

src/core.c/Grammar.pm6

@@ -28,9 +28,9 @@ my class Grammar is Match {
                   ),
                   $match := ($cursor := $cursor.'!cursor_next'()).MATCH
                 ),
-                $match || Nil,
+                $match || Nil
               ),
-              Nil,
+              Nil
             )
           )
         )

src/core.c/core_prologue.pm6

@@ -1,3 +1,7 @@
+# This constant must specify current CORE revision.
+# Must preceede class declarations to allow correct recording of their respective language version.
+my constant CORE-SETTING-REV = 'c';
+
 # Stub a few things the compiler wants to have really early on.
 my class Pair { ... }   # must be first for some reason
 my class Block { ... }
@@ -67,7 +71,4 @@ PROCESS::<$SCHEDULER> = JavaScriptScheduler.new();
 BEGIN {nqp::p6setassociativetype(Associative);}
 #?endif
 
-# This constant must specify current CORE revision
-my constant CORE-SETTING-REV = 'c';
-
 # vim: ft=perl6 expandtab sw=4

src/core.d/core_prologue.pm6

@@ -1,6 +1,7 @@
 use nqp;
 
 # This constant must specify current CORE revision
+# Must preceede class declarations to allow correct recording of their respective language version.
 my constant CORE-SETTING-REV = 'd';
 
 # vim: ft=perl6 expandtab sw=4

src/core.e/EXPORTHOW.pm6

@@ -0,0 +1,17 @@
+# Bind the HOWs into the EXPORTHOW package under the package declarator
+# names.
+
+{
+    # Don't expose this name in CORE's namespace
+    class Perl6::Metamodel::v6e::GrammarHOW
+        is Perl6::Metamodel::ClassHOW
+        does Perl6::Metamodel::DefaultParent
+    {
+    }
+
+    # Set 6.e Grammar as the default for grammars
+    Perl6::Metamodel::v6e::GrammarHOW.set_default_parent_type(Grammar);
+    EXPORTHOW.WHO<grammar> := Perl6::Metamodel::v6e::GrammarHOW;
+}
+
+# vim: ft=perl6 expandtab sw=4

src/core.e/core_prologue.pm6

@@ -1,6 +1,7 @@
 use nqp;
 
 # This constant must specify current CORE revision
+# Must preceede class declarations to allow correct recording of their respective language version.
 my constant CORE-SETTING-REV = 'e';
 
 # vim: ft=perl6 expandtab sw=4

tools/templates/6.e/core_sources

@@ -1,3 +1,4 @@
 src/core.e/core_prologue.pm6
 src/core.e/PseudoStash.pm6
 src/core.e/Grammar.pm6
+src/core.e/EXPORTHOW.pm6