# HG changeset patch
# User Stefan Vogel <sv@exept.de>
# Date 1467298753 -7200
# Node ID e913680689bfeb5766f535ea1c029dfa1e0b12a8
# Parent  cbe2e415bb782547114f69d14b172a0792b85bb8
#REFACTORING by stefan
class: Lazy
added: #_evaluate_
comment/format in:
        #block:
        #examples
changed: #doesNotUnderstand:
    protocol compatibility with LazyValue
    nil Semaphores when evaluated.

diff -r cbe2e415bb78 -r e913680689bf Lazy.st
--- a/Lazy.st	Wed Jun 29 18:27:52 2016 +0200
+++ b/Lazy.st	Thu Jun 30 16:59:13 2016 +0200
@@ -76,49 +76,51 @@
 "
   Evaluates the factorial, starting only when the
   result is actually required (when printString is sent).
-						[exBegin]
+                                                [exBegin]
     | fac |
     fac := [100 factorial] lazyValue.
     Transcript showCR: 'Doing nothing. '.
     (Delay forSeconds: 2) wait.
     Transcript showCR: fac printString.
-						[exEnd]
+                                                [exEnd]
 
 
-  Starts evaluating both factorials only when required (by the touch),
+  Starts evaluating both factorials only when required (by the value),
   and waits until both blocks have finished before continuing.
-						[exBegin]
+                                                [exBegin]
     | fac1 fac2 |
     fac1 := [Transcript showCR: 'Starting fac1.. '. 100 factorial] lazyValue.
     fac2 := [Transcript showCR: 'Starting fac2.. '. 120 factorial] lazyValue.
-    fac2 touch.
-    fac1 touch.
+    fac2 value.
+    fac1 value.
     Transcript showCR: 'both completed.'.
-						[exEnd]
+                                                [exEnd]
 
 
   Demonstrates how to pass arguments to a lazy evaluation block.
-						[exBegin]
+                                                [exBegin]
     | temp |
     temp := [:x :y :z | x * y * z] lazyValueWithArguments: #(2 3 4).
     Transcript  showCR: temp printString.
-						[exEnd]
+                                                [exEnd]
 "
 ! !
 
 !Lazy methodsFor:'evaluating'!
 
 block: aBlock
-	"Execute aBlock in parallel, but ensure that any messages sent
-	 to me before execution of the block has terminated are
-	 suspended until it has terminated. Do not start the evaluation
-	 until at least one message has been sent to the receiver."
+    "Execute aBlock in parallel, but ensure that any messages sent
+     to me before execution of the block has terminated are
+     suspended until it has terminated. Do not start the evaluation
+     until at least one message has been sent to the receiver."
 
-	startSemaphore := Semaphore new.
-	endSemaphore := Semaphore new.
-	[startSemaphore wait.
-	 result := aBlock value.
-	 endSemaphore signal] fork
+    startSemaphore := Semaphore new.
+    endSemaphore := Semaphore new.
+    [
+        startSemaphore wait.
+        result := aBlock value.
+        endSemaphore signal
+    ] fork.
 !
 
 block: aBlock value: aValue
@@ -175,13 +177,28 @@
 
 !Lazy methodsFor:'synchronising'!
 
+_evaluate_
+    "answer the computed value"
+
+    |startSema endSema|
+
+    startSema := startSemaphore.
+    startSema notNil ifTrue:[
+        startSema signal.          "Start the evaluation."
+        endSema := endSemaphore.
+        endSema notNil ifTrue:[
+            endSema waitUncounted.     "Wait until evaluation completed."
+        ].
+        startSemaphore := endSemaphore := nil.
+    ].
+
+    ^ result
+!
+
 doesNotUnderstand: aMessage
     "Any message to a Lazy will end up here."
 
-    startSemaphore signal.          "Start the evaluation."
-    endSemaphore waitUncounted.     "Wait until evaluation completed."
-
-    ^ aMessage sendTo:result
+    ^ aMessage sendTo:self _evaluate_
 ! !
 
 !Lazy methodsFor:'testing'!