clarified operations;

--- a/src/Pure/Concurrent/lazy.ML	Mon Feb 19 11:29:08 2018 +0100
+++ b/src/Pure/Concurrent/lazy.ML	Mon Feb 19 14:18:29 2018 +0100
@@ -13,13 +13,16 @@
   val lazy_name: string -> (unit -> 'a) -> 'a lazy
   val lazy: (unit -> 'a) -> 'a lazy
   val peek: 'a lazy -> 'a Exn.result option
+  val is_pending: 'a lazy -> bool
   val is_running: 'a lazy -> bool
   val is_finished: 'a lazy -> bool
   val force_result: 'a lazy -> 'a Exn.result
   val force: 'a lazy -> 'a
   val force_list: 'a lazy list -> 'a list
-  val forced: 'a lazy -> 'a lazy
+  val force_value: 'a lazy -> 'a lazy
+  val trim_value: 'a lazy -> 'a lazy
   val map: ('a -> 'b) -> 'a lazy -> 'b lazy
+  val map_finished: ('a -> 'b) -> 'a lazy -> 'b lazy
   val future: Future.params -> 'a lazy -> 'a future
 end;
 
@@ -46,17 +49,17 @@
         Expr _ => NONE
       | Result res => Future.peek res);
 
-fun pending (Value _) = false
-  | pending (Lazy var) =
-      (case Synchronized.value var of
-        Expr _ => true
-      | Result _ => false);
+
+(* status *)
 
 fun is_value (Value _) = true
   | is_value (Lazy _) = false;
 
-
-(* status *)
+fun is_pending (Value _) = false
+  | is_pending (Lazy var) =
+      (case Synchronized.value var of
+        Expr _ => true
+      | Result _ => false);
 
 fun is_running (Value _) = false
   | is_running (Lazy var) =
@@ -109,13 +112,19 @@
 fun force x = Exn.release (force_result x);
 
 fun force_list xs =
-  (List.app (fn x => if pending x then ignore (force_result x) else ()) xs;
+  (List.app (fn x => if is_pending x then ignore (force_result x) else ()) xs;
    map force xs);
 
-fun forced x = if is_value x then x else value (force x);
+fun force_value x = if is_value x then x else value (force x);
+fun trim_value x = if is_pending x then x else force_value x;
+
+
+(* map *)
 
 fun map f x = lazy_name "Lazy.map" (fn () => f (force x));
 
+fun map_finished f x = if is_finished x then value (f (force x)) else map f x;
+
 
 (* future evaluation *)