--- a/Interval.st	Fri Jul 16 11:39:45 1993 +0200
+++ b/Interval.st	Mon Oct 04 11:32:33 1993 +0100
@@ -39,25 +39,21 @@
     "return a new interval with elements from start
      to stop by 1"
 
-    ^ self new
-        setFrom:start 
-        to:stop
-        by:1
+    ^ self new setFrom:start to:stop by:1
 !
 
 from:start to:stop by:step
     "return a new interval with elements from start
      to stop by step"
 
-    ^ self new
-        setFrom:start
-        to:stop
-        by:step
+    ^ self new setFrom:start to:stop by:step
 ! !
 
 !Interval methodsFor:'private'!
 
 setFrom:startInteger to:stopInteger by:stepInteger
+    "set start, stop and step components"
+
     start := startInteger.
     stop := stopInteger.
     step := stepInteger
@@ -71,6 +67,12 @@
     ^ start
 !
 
+last
+    "return the last element of the collection"
+
+    ^ stop
+!
+
 start
     "return the first number of the range"
 
@@ -123,6 +125,8 @@
 !
 
 at:index
+    "return (i.e. compute) the index'th element"
+
     (index between:1 and:self size) ifTrue:[
         ^ start + (step * (index - 1))
     ].
@@ -130,16 +134,22 @@
 !
 
 at:index put:anObject
+    "catch at:put: message - intervals cannot store elements"
+
     self error:'you cannot store into an interval'
 ! !
 
 !Interval methodsFor:'adding/removing elements'!
 
 add:newObject
+    "catch add message - intervals cannot add elements"
+
     self error:'elements cannot be added to an interval'
 !
 
 remove:anObject
+    "catch remove message - intervals cannot remove elements"
+
     self error:'elements cannot be removed from an interval'
 ! !
 
@@ -149,9 +159,49 @@
     ^ OrderedCollection
 ! !
     
+!Interval methodsFor:'printing & storing'!
+
+printString
+    "return a string for informal printing"
+
+    ^ self storeString
+!
+
+displayString
+    ^ 'Interval(' , self storeString , ')'
+!
+
+storeString
+    "return a string for storing"
+
+    step = 1 ifTrue:[
+        ^ start storeString , ' to:' , stop storeString
+    ].
+    ^ start storeString , ' to:' , stop storeString , ' by:' , step storeString
+
+    "(1 to:10) storeString"
+    "(1 to:10 by:2) storeString"
+!
+
+storeOn:aStream
+    start storeOn:aStream.
+    aStream nextPutAll:' to:'.
+    stop storeOn:aStream.
+    step ~= 1 ifTrue:[
+        aStream nextPutAll:' by:'.
+        step storeOn:aStream.
+    ].
+
+    "(1 to:10) storeOn:Transcript"
+    "(1 to:10 by:2) storeOn:Transcript"
+! !
+
 !Interval methodsFor:'enumeration'!
 
 do:aBlock
+    "evaluate the argument, aBlock for every element in the
+     receiver-interval"
+
     |aValue|
 
     aValue := start.
@@ -176,7 +226,7 @@
 
     |newColl|
 
-    newColl := OrderedCollection new:self size.
+    newColl := self species new:self size.
     self do:[:each |
         (aBlock value:each) ifTrue:[newColl add:each]
     ].