regression/opaque.sml

   1 (* From Chapter 5 of Elsman's PhD thesis; these examples should
   2  * elaborate. *)
   3
   4 (* Decrease in generativity *)
   5
   6 functor f() = struct type a = int
   7                      val a = 232
   8                      val pr = Int.toString
   9               end :> sig type a
  10                          val a : a
  11                          val pr : a -> string
  12                      end
  13
  14 structure f = f()
  15 val _ = print ("f.a = " ^ f.pr f.a ^ "\n")
  16
  17 functor g() = struct datatype a = A | B
  18                      fun pr_a A = "A"
  19                        | pr_a B = "B"
  20                      val pr_b = pr_a
  21                      type b = a
  22               end :> sig type a type b
  23                          val A : a
  24                          val B : b
  25                          val pr_a : a -> string
  26                          val pr_b : b -> string
  27                      end
  28
  29 structure g = g()
  30 val _ = print ("g.A = " ^ g.pr_a g.A ^ "\n")
  31 val _ = print ("g.B = " ^ g.pr_b g.B ^ "\n")
  32
  33
  34 functor h(s : sig type a val pr : a -> string val a : a end) =
  35   struct
  36     val pr = s.pr
  37     val b = s.a
  38     type b = s.a
  39   end :> sig type b
  40              val pr : b -> string
  41              val b : b
  42          end
  43
  44 structure h = h(struct type a = int val pr = Int.toString val a = 343 end)
  45 val _ = print ("h.b = " ^ h.pr h.b ^ "\n")
  46
  47 (* Increase in generativity *)
  48
  49 functor i() = struct datatype a = A
  50                      and b = B | C
  51                      type c = a * b
  52                      val c = (A,C)
  53                      fun pr (A,B) = "(A,B)"
  54                        | pr (A,C) = "(A,C)"
  55               end :> sig type c val c : c val pr : c -> string end
  56
  57 structure i = i()
  58 val _ = print ("i.c = " ^ i.pr i.c ^ "\n")
  59
  60 (* Signature S below is well-formed, but after opacity elimination it
  61  * is not. No real structure (i.e., a structure existing outside of a
  62  * functor body) can match the signature S. The signature should
  63  * elaborate, however. *)
  64
  65 structure S = struct type s = int * int
  66               end :> sig eqtype s end
  67
  68 signature S = sig datatype u = A
  69               end where type u = S.s