Fix for #126897

And some code layout and doc

src/core/Slip.pm

@@ -1,14 +1,15 @@
 # A Slip is a kind of List that is immediately incorporated into an iteration
 # or another List. Other than that, it's a totally normal List.
-my class Slip {
+my class Slip { # is List
     multi method Slip(Slip:D:) { self }
-    method defined () { self.so }
-    method CALL-ME (+args) { args.Slip }
+    method defined ()          { self.so }
+    method CALL-ME (+args)     { args.Slip }
+    multi method perl(Slip:D:) { 'slip' ~ callsame }
 }
 
 # The slip(...) function creates a Slip.
-proto slip(|) { * }
-multi slip() { Empty }
+proto slip(|)     { * }
+multi slip()      { Empty }
 multi slip(+args) { args.Slip }
 
 # vim: ft=perl6 expandtab sw=4