list a ::= Nil | Cons a (list a); ;;

ccat xss k =
case xss of
   Nil -> k Nil;
   Cons xs xss2 -> ccat xss2 (\ys -> capp xs ys k)
end;

capp l ys cont
   = case l of
        Nil -> cont ys;
        Cons x xs -> capp xs ys (\zs -> cont (Cons x zs))
     end;