--- a/Interval.st	Tue Aug 15 16:30:53 2000 +0200
+++ b/Interval.st	Tue Aug 15 16:31:18 2000 +0200
@@ -10,6 +10,8 @@
  hereby transferred.
 "
 
+"{ Package: 'stx:libbasic' }"
+
 SequenceableCollection subclass:#Interval
 	instanceVariableNames:'start stop step'
 	classVariableNames:''
@@ -84,9 +86,9 @@
     "return (i.e. compute) the index'th element"
 
     (index between:1 and:self size) ifTrue:[
-	^ start + (step * (index - 1))
+        ^ start + (step * (index - 1))
     ].
-    self errorSubscriptBounds:index
+    ^ self subscriptBoundsError:index
 !
 
 at:index put:anObject
@@ -100,6 +102,10 @@
 first
     "return the first element of the collection"
 
+    (((step < 0) and:[start < stop])
+    or:[(step > 0) and:[stop < start]]) ifTrue:[
+        ^ self emptyCollectionError
+    ].
     ^ start
 !
 
@@ -112,6 +118,10 @@
 last
     "return the last element of the collection"
 
+    (((step < 0) and:[start < stop])
+    or:[(step > 0) and:[stop < start]]) ifTrue:[
+        ^ self emptyCollectionError
+    ].
     ^ stop
 !
 
@@ -324,5 +334,5 @@
 !Interval class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/Interval.st,v 1.25 1999-05-08 13:25:13 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/Interval.st,v 1.26 2000-08-15 14:31:18 cg Exp $'
 ! !