diff --git a/lib/inference.ml b/lib/inference.ml
index 4a3ad5b..89b5e96 100644
--- a/lib/inference.ml
+++ b/lib/inference.ml
@@ -35,9 +35,10 @@ let typeof t =
           | None, _ -> Some (Type.Arrow (Type.Var id, ty_body)), env')
        | _ -> None, env)
     | Term.App (t1, t2) ->
-      (* Check if the function type matches the arguments *)
+      (* TODO: When a variable is a function *)
       (match infer env t1, infer env t2 with
        | (Some (Type.Arrow (ty_param, ty_fn)), _), (Some ty_args, _) ->
+         (* Check if the function type matches the arguments *)
          (match Unification.unify ty_param ty_args with
           | Some _ -> Some ty_fn, env
           | None -> None, env)