regression/fail/modules.51.sml

   1 (*
   2  * This example tests that a variable type containing unknown types is not
   3  * mistakenly generalized when matching a signature.
   4  *)
   5 structure S:
   6    sig
   7       val f: 'a option -> 'a option
   8    end =
   9    struct
  10       val f =
  11          let
  12             val r = ref NONE
  13          in
  14             fn z => (!r before (r := z))
  15          end
  16    end
  17
  18 val _ = S.f (SOME 13)
  19
  20 val _ =
  21    case S.f (SOME (fn z => z)) of
  22       NONE => 15
  23     | SOME f => f 17