[MLton-commit] r5060

[Vesa Karvonen]

Initial commit of a lib of misc utils to be refactored.
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A   mltonlib/trunk/com/ssh/misc-util/unstable/type-info.sml

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Added: mltonlib/trunk/com/ssh/misc-util/unstable/type-info.sml
===================================================================
--- mltonlib/trunk/com/ssh/misc-util/unstable/type-info.sml	2007-01-12 12:37:27 UTC (rev 5059)
+++ mltonlib/trunk/com/ssh/misc-util/unstable/type-info.sml	2007-01-12 12:37:50 UTC (rev 5060)
@@ -0,0 +1,134 @@
+(* Copyright (C) 2007 SSH Communications Security, Helsinki, Finland
+ *
+ * This code is released under the MLton license, a BSD-style license.
+ * See the LICENSE file or http://mlton.org/License for details.
+ *)
+
+(*
+ * An implementation of a type-indexed function for tracking a number of
+ * important type properties.
+ *
+ * These type properties can be useful for both optimizations and for
+ * ensuring correctness.  As an optimization one could, for example,
+ * determine whether one needs to handle cyclic values (which can be
+ * costly) or not.  As a correctness issue, one can avoid generating
+ * infinite data structures or avoid performing non-terminating operations
+ * on infinite data structures.
+ *
+ * This type-indexed function is unlikely to be directly useful in
+ * application programs and is more likely to be used internally in the
+ * implementation of some other type-indexed functions (e.g. pickling).
+ *)
+
+signature TYPE_INFO = sig
+   type 'a type_info_t
+
+   val hasExn : 'a type_info_t UnPr.t
+   (** Returns true iff the type {'a} contains the type {exn}. *)
+
+   val hasRecData : 'a type_info_t UnPr.t
+   (**
+    * Returns true iff the type {'a} contains recursive references to
+    * datatypes.
+    *)
+
+   val isRefOrArray : 'a type_info_t UnPr.t
+   (**
+    * Returns true iff the type {'a} is of the form {'b array} or of
+    * the form {'b ref}.
+    *)
+
+   val canBeCyclic : 'a type_info_t UnPr.t
+   (**
+    * Returns true iff {'a} is of the form {'b ref} or {'b array} and
+    * it can not be ruled out that values of the type can form cycles.
+    *
+    * Note: Functions are not considered to form cycles.
+    *)
+end
+
+functor LiftTypeInfo
+           (include TYPE_INFO
+            type 'a t
+            val lift : ('a type_info_t, 'a t) Lift.t Thunk.t) : TYPE_INFO = struct
+   type 'a type_info_t = 'a t
+   val hasExn       = fn ? => Lift.get lift hasExn       ?
+   val hasRecData   = fn ? => Lift.get lift hasRecData   ?
+   val isRefOrArray = fn ? => Lift.get lift isRefOrArray ?
+   val canBeCyclic  = fn ? => Lift.get lift canBeCyclic  ?
+end
+
+structure TypeInfo :> sig
+   include STRUCTURAL_TYPE
+   include TYPE_INFO where type 'a type_info_t = 'a t
+end = struct
+   datatype u = IN of {exn : Bool.t, pure : Bool.t, recs : Int.t List.t}
+   fun out (IN t) = t
+   type 'a t = u
+   type 'a type_info_t = 'a t
+
+   val hasExn = #exn o out
+   val hasRecData = not o null o #recs o out
+   val isRefOrArray = not o #pure o out
+   val canBeCyclic = isRefOrArray andAlso (hasExn orElse hasRecData)
+
+   val base = IN {exn = false, pure = true, recs = []}
+   fun pure (IN {exn, recs, ...}) = IN {exn = exn, pure = true, recs = recs}
+   fun impure (IN {exn, recs, ...}) =
+       IN {exn = exn, pure = false, recs = recs}
+   fun combine (IN {exn = hl, recs = rl, ...},
+                IN {exn = hr, recs = rr, ...}) =
+       IN {exn = hl orelse hr, pure = true,
+           recs = SortedList.merge#1 Int.compare (rl, rr)}
+
+   val iso = const
+
+   val op *` = combine
+   val op +` = combine
+
+   val unit = base
+
+   local
+      val id = ref 0
+   in
+      fun Y ? =
+          Tie.pure
+             (fn () => let
+                 val this = !id before id += 1
+              in
+                 (IN {exn = false, pure = true, recs = [this]},
+                  fn IN {exn, pure, recs} =>
+                     IN {exn = exn, pure = pure,
+                         recs = SortedList.remove
+                                   #1 Int.compare this recs})
+              end) ?
+   end
+
+   fun _ --> _ = base
+
+   val exn = IN {exn = true, pure = true, recs = []}
+   fun regExn _ _ = ()
+
+   val array = impure
+   val refc  = impure
+
+   val vector = pure
+
+   val largeInt  = base
+   val largeReal = base
+   val largeWord = base
+
+   val list = pure
+
+   val bool   = base
+   val char   = base
+   val int    = base
+   val real   = base
+   val string = base
+   val word   = base
+
+   val word8  = base
+   val word16 = base
+   val word32 = base
+   val word64 = base
+end


Property changes on: mltonlib/trunk/com/ssh/misc-util/unstable/type-info.sml
___________________________________________________________________
Name: svn:eol-style
   + native