--- a/DIVariableTable.st	Wed May 27 15:47:18 2020 +0100
+++ b/DIVariableTable.st	Tue Jun 09 14:01:25 2020 +0100
@@ -1,6 +1,7 @@
 "
  COPYRIGHT (c) 1989 by Claus Gittinger / eXept Software AG
  COPYRIGHT (c) 2016 Jan Vrany
+ COPYRIGHT (c) 2020 LabWare
               All Rights Reserved
 
  This software is furnished under a license and may be used
@@ -27,6 +28,7 @@
 "
  COPYRIGHT (c) 1989 by Claus Gittinger / eXept Software AG
  COPYRIGHT (c) 2016 Jan Vrany
+ COPYRIGHT (c) 2020 LabWare
               All Rights Reserved
 
  This software is furnished under a license and may be used
@@ -61,10 +63,14 @@
 !DIVariableTable methodsFor:'adding & removing'!
 
 addVariable: aDIVariable
+    (variables includes: aDIVariable) ifTrue:[ 
+        self error: 'Oops, trying to add the same variable twice?'
+    ].
     variables := variables copyWith: aDIVariable.
     variables_count := variables_count + 1
 
     "Created: / 14-07-2018 / 20:52:01 / Jan Vrany <jan.vrany@fit.cvut.cz>"
+    "Modified: / 09-06-2020 / 13:25:54 / Jan Vrany <jan.vrany@labware.com>"
 !
 
 addVariableNamed:aString isArgument:aBoolean offset:anOnteger physicalBlock: physical lexicalBlock: lexical
@@ -123,3 +129,10 @@
     "Created: / 15-07-2018 / 11:27:36 / Jan Vrany <jan.vrany@fit.cvut.cz>"
 ! !
 
+!DIVariableTable class methodsFor:'documentation'!
+
+version_HG
+
+    ^ '$Changeset: <not expanded> $'
+! !
+