hide which exact functors the barrier needs

theories/functions.v

@@ -31,20 +31,41 @@ Section functions.
 End functions.
 
 (** "Cons-ing" of functions from nat to T *)
+(* Coq's standard lists are not universe polymorphic. Hence we have to re-define them. Ouch.
+   TODO: If we decide to end up going with this, we should move this elsewhere. *)
+Polymorphic Inductive plist {A : Type} : Type :=
+| pnil : plist
+| pcons: A → plist → plist.
+Arguments plist : clear implicits.
+
+Polymorphic Fixpoint papp {A : Type} (l1 l2 : plist A) : plist A :=
+  match l1 with
+  | pnil => l2
+  | pcons a l => pcons a (papp l l2)
+  end.
+
+(* TODO: Notation is totally up for debate. *)
+Infix "`::`" := pcons (at level 60, right associativity) : C_scope.
+Infix "`++`" := papp (at level 60, right associativity) : C_scope.
+
 Polymorphic Definition fn_cons {T : Type} (t : T) (f: nat → T) : nat → T :=
   λ n, match n with
        | O => t
        | S n => f n
        end.
 
-Polymorphic Definition fn_mcons {T : Type} (ts : list T) (f : nat → T) : nat → T :=
-    fold_right fn_cons f ts.
+Polymorphic Fixpoint fn_mcons {T : Type} (ts : plist T) (f : nat → T) : nat → T :=
+  match ts with
+  | pnil => f
+  | pcons t ts => fn_cons t (fn_mcons ts f)
+  end.
 
+(* TODO: Notation is totally up for debate. *)
 Infix ".::" := fn_cons (at level 60, right associativity) : C_scope.
 Infix ".++" := fn_mcons (at level 60, right associativity) : C_scope.
 
-Polymorphic Lemma fn_mcons_app {T : Type} (ts1 ts2 : list T) f :
-  (ts1 ++ ts2) .++ f = ts1 .++ (ts2 .++ f).
+Polymorphic Lemma fn_mcons_app {T : Type} (ts1 ts2 : plist T) f :
+  (ts1 `++` ts2) .++ f = ts1 .++ (ts2 .++ f).
 Proof.
-  unfold fn_mcons. rewrite fold_right_app. done.
+  induction ts1; simpl; eauto. congruence.
 Qed.