History variables: Difference between revisions

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@@ Line 595: / Line 595: @@
 </lang>
 =={{header|Elena}}==
-ELENA 3.4 :
+ELENA 4.x :
-<lang elena>import extensions.
+<lang elena>import extensions;
-import system'collections.
+import system'collections;
-import system'routines.
+import system'routines;
-import extensions'routines.
+import extensions'routines;
 class HistoryVariable
 {
-    T<Stack> _previous := Stack new.
+    Stack  previous := new Stack();
+    object value;
-    object prop Value :: _value.
+    prop object Value
+    {
+        get() = value;
-    set Value:v
-    [
-        if (nil != _value)
+        set(value)
-        [
+        {
-            _previous push(_value)
+            if ((this value) != nil)
-        ].
+            {
+                previous.push(this value)
+            };
+            this value := value
+        }
+    }
-        _value := v
+    undo()
-    ]
+    {
+        ifnot (previous.isEmpty())
+        {
+            value := previous.pop()
+        }
+        else
+        {
+            value := nil
+        }
+    }
+    enumerator() => previous;
-    undo
-    [
-        ifnot (_previous isEmpty)
-        [
-            _value := _previous pop
-        ];
-        [
-            _value := nilValue
-        ]
-    ]
+    get string Printable() => this value;
-    enumerator => _previous.
-    T<literal> literal => _value.
 }
-public program
+public program()
+{
-[
-    var o := HistoryVariable new.
+    var o := new HistoryVariable();
-    o Value := 5.
+    o.Value := 5;
-    o Value := "foo".
+    o.Value := "foo";
-    o Value := o Value + "bar".
+    o.Value := o.Value + "bar";
-    console printLine(o).
+    console.printLine(o);
-    o forEach:printingLn.
+    o.forEach:printingLn;
-    o undo; undo; undo.
+    o.undo().undo().undo();
-    console printLine(o Value).
+    console.printLine(o.Value ?? "nil")
-]</lang>
+}</lang>
 {{out}}
 <pre>
@@ Line 653: / Line 658: @@
 foo
+nil
 </pre>