clarified modules;

--- a/src/Pure/Concurrent/unsynchronized.ML	Sat Apr 02 20:23:51 2016 +0200
+++ b/src/Pure/Concurrent/unsynchronized.ML	Sat Apr 02 20:33:34 2016 +0200
@@ -28,3 +28,6 @@
     in Exn.release result end) ();
 
 end;
+
+val _ = ML_Name_Space.forget_val "ref";
+val _ = ML_Name_Space.forget_type "ref";

--- /dev/null	Thu Jan 01 00:00:00 1970 +0000
+++ b/src/Pure/ML/ml_pervasive.ML	Sat Apr 02 20:33:34 2016 +0200
@@ -0,0 +1,22 @@
+(*  Title:      Pure/ML/ml_pervasive.ML
+    Author:     Makarius
+
+Pervasive ML environment.
+*)
+
+val seconds = Time.fromReal;
+
+val _ =
+  List.app ML_Name_Space.forget_val
+    ["isSome", "getOpt", "valOf", "foldl", "foldr", "print", "explode", "concat"];
+
+val ord = SML90.ord;
+val chr = SML90.chr;
+val raw_explode = SML90.explode;
+val implode = SML90.implode;
+
+val pointer_eq = PolyML.pointerEq;
+
+val error_depth = PolyML.error_depth;
+
+open Thread;

--- a/src/Pure/ROOT	Sat Apr 02 20:23:51 2016 +0200
+++ b/src/Pure/ROOT	Sat Apr 02 20:33:34 2016 +0200
@@ -112,6 +112,7 @@
     "ML/ml_name_space.ML"
     "ML/ml_options.ML"
     "ML/ml_pp.ML"
+    "ML/ml_pervasive.ML"
     "ML/ml_pretty.ML"
     "ML/ml_profiling.ML"
     "ML/ml_statistics.ML"

--- a/src/Pure/ROOT.ML	Sat Apr 02 20:23:51 2016 +0200
+++ b/src/Pure/ROOT.ML	Sat Apr 02 20:33:34 2016 +0200
@@ -6,6 +6,7 @@
 
 use "ML/ml_system.ML";
 use "ML/ml_name_space.ML";
+use "ML/ml_pervasive.ML";
 
 if List.exists (fn (a, _) => a = "FixedInt") (#allStruct ML_Name_Space.global ()) then ()
 else use "ML/fixed_int_dummy.ML";
@@ -22,50 +23,16 @@
 
 use "General/exn.ML";
 
-val seconds = Time.fromReal;
-
-open Thread;
 use "Concurrent/multithreading.ML";
-
 use "Concurrent/unsynchronized.ML";
-val _ = ML_Name_Space.forget_val "ref";
-val _ = ML_Name_Space.forget_type "ref";
 
 
-(* pervasive environment *)
-
-val _ =
-  List.app ML_Name_Space.forget_val
-    ["isSome", "getOpt", "valOf", "foldl", "foldr", "print", "explode", "concat"];
-
-val ord = SML90.ord;
-val chr = SML90.chr;
-val raw_explode = SML90.explode;
-val implode = SML90.implode;
-
-
-(* ML runtime system *)
+(* ML system *)
 
 use "ML/ml_heap.ML";
 use "ML/ml_profiling.ML";
-
-val pointer_eq = PolyML.pointerEq;
-
-
-(* ML toplevel pretty printing *)
-
 use "ML/ml_pretty.ML";
-
-val error_depth = PolyML.error_depth;
-
-
-(* ML compiler *)
-
 use "ML/ml_compiler0.ML";
-
-
-(* ML debugger *)
-
 use_no_debug "ML/ml_debugger.ML";