src/HOL/Tools/functor.ML

--- a/src/HOL/Tools/functor.ML	Thu Jan 11 12:32:07 2018 +0100
+++ b/src/HOL/Tools/functor.ML	Thu Jan 11 13:48:17 2018 +0100
@@ -199,7 +199,7 @@
       | add_tycos _ = I;
     val tycos = add_tycos T [];
     val tyco = if tycos = ["fun"] then "fun"
-      else case remove (=) "fun" tycos
+      else case remove (op =) "fun" tycos
        of [tyco] => tyco
         | _ => error ("Bad number of type constructors: " ^ Syntax.string_of_typ ctxt T);
   in (mapper, T, tyco) end;