Implement Capture.WHICH

src/core/Capture.pm

@@ -11,6 +11,22 @@ my class Capture { # declared in BOOTSTRAP
         nqp::bindattr(self, Capture, '$!hash', nqp::ishash($hs) ?? $hs !! nqp::hash());
         1;
     }
+    submethod WHICH {
+        my $WHICH = self.^name;
+        if self.defined {
+            if $!list {
+                $WHICH ~= '|';
+                $WHICH ~= ( '(' ~ $_.WHICH ~ ')' )
+                  for $!list;
+            }
+            if $!hash {
+                $WHICH ~= '|';
+                $WHICH ~= ( $_ ~ '(' ~ $!hash{$_}.WHICH ~ ')' )
+                  for $!hash.keys.sort;
+            }
+        }
+        $WHICH;
+    }
 
     method at_key(Capture:D: $key is copy) {
         $key = $key.Str;

src/core/core_epilogue.pm

@@ -14,6 +14,16 @@ BEGIN {
     Perl6::Metamodel::GrammarHOW.HOW.compose(Perl6::Metamodel::GrammarHOW);
 }
 
+multi sub trait_mod:<is>(Routine $r, :$cached!) {
+    my %cache;
+    $r.wrap(-> |c {
+        my $WHICH := c.WHICH;
+        %cache{$WHICH}:exists
+          ?? %cache{$WHICH}
+          !! (%cache{$WHICH} = callsame);
+    });
+}
+
 {YOU_ARE_HERE}
 
 # vim: ft=perl6 expandtab sw=4