Add a $!shared to cursor, for parse-wide things.

We'll move $!orig and $!target in to here. This will mean they need not
both be copied into every Cursor, meaning we'll save a word per Cursor,
at the cost of a little extra indirection occasionally. Also this will
be a good place to hang certain other things.

Author: jnthn

src/HLL/Grammar.pm

@@ -801,7 +801,7 @@ An operator precedence parser.
     }
 
     method LANG($lang, $regex, *@args) {
-        my $lang_cursor := %*LANG{$lang}.'!cursor_init'(self.orig(), :p(self.pos()), :target(self.target()));
+        my $lang_cursor := %*LANG{$lang}.'!cursor_init'(self.orig(), :p(self.pos()), :target(self.target()), :shared(self.'!shared'()));
         if self.HOW.traced(self) {
             $lang_cursor.HOW.trace-on($lang_cursor, self.HOW.trace_depth(self));
         }

src/QRegex/Cursor.nqp

@@ -1,4 +1,9 @@
+# Some things that all cursors involved in a given parse share.
+my class ParseShared {
+}
+
 role NQPCursorRole is export {
+    has $!shared;
     has $!orig;
     has str $!target;
     has int $!from;
@@ -65,8 +70,10 @@ role NQPCursorRole is export {
         $caps;
     }
 
-    method !cursor_init($orig, :$p = 0, :$c, :$target) {
+    method !cursor_init($orig, :$p = 0, :$c, :$target, :$shared) {
         my $new := self.CREATE();
+        $shared := nqp::create(ParseShared) unless $shared;
+        nqp::bindattr($new, $?CLASS, '$!shared', $shared);
         nqp::bindattr($new, $?CLASS, '$!orig', $orig);
         nqp::bindattr_s($new, $?CLASS, '$!target', $target
             ?? $target
@@ -190,6 +197,8 @@ role NQPCursorRole is export {
         nqp::findmethod($actions, $name)($actions, $match, $key)
             if !nqp::isnull($actions) && nqp::can($actions, $name);
     }
+    
+    method !shared() { $!shared }
 
     my @EMPTY := [];
     method !protoregex($name) {