--- a/Character.st	Mon Aug 17 17:36:37 2009 +0200
+++ b/Character.st	Tue Aug 18 00:07:57 2009 +0200
@@ -1426,11 +1426,7 @@
       A major advantage of rot13 over rot(N) for other N is that it
       is self-inverse, so the same code can be used for encoding and decoding."
 
-    (((self >= $a) and:[self < $n]) or:[(self >= $A) and:[self < $N]])
-	ifTrue: [ ^ self + 13 ].
-    (((self > $m) and:[self <= $z]) or:[(self > $M) and:[self <= $Z]])
-	ifTrue: [ ^ self - 13 ].
-    ^ self
+    ^ self rot:13
 
     "
      $h rot13
@@ -1438,6 +1434,31 @@
      'The butler did it!!' rot13             -> 'Gur ohgyre qvq vg!!'
      'The butler did it!!' rot13 rot13       -> 'The butler did it!!'
     "
+!
+
+rot:n
+     "Usenet: from `rotate alphabet N places']
+      The simple Caesar-cypher encryption that replaces each English
+      letter with the one N places forward or back along the alphabet,
+      so that 'The butler did it!!' becomes 'Gur ohgyre qvq vg!!' by rot:13
+      Most Usenet news reading and posting programs include a rot13 feature.
+      It is used to enclose the text in a sealed wrapper that the reader must choose
+      to open -- e.g., for posting things that might offend some readers, or spoilers.
+      A major advantage of rot13 over rot(N) for other N is that it
+      is self-inverse, so the same code can be used for encoding and decoding."
+
+    (self isLetter) ifTrue:[
+        self isLowercase ifTrue:[
+            ^ 'abcdefghijklmnopqrstuvwxyzabcdefghijklmnopqrstuvwxyz' at:(self-$a+1+n)
+        ].
+        ^ 'ABCDEFGHIJKLMNOPQRSTUVWXYZABCDEFGHIJKLMNOPQRSTUVWXYZ' at:(self-$A+1+n)
+    ].
+    ^ self
+
+    "
+     'The butler did it!!' rot:13                -> 'Gur ohgyre qvq vg!!'
+     ('The butler did it!!' rot:13) rot:13       -> 'The butler did it!!'
+    "
 ! !
 
 
@@ -2746,5 +2767,5 @@
 !Character class methodsFor:'documentation'!
 
 version
-    ^ '$Header: /cvs/stx/stx/libbasic/Character.st,v 1.136 2009-03-23 14:44:16 cg Exp $'
+    ^ '$Header: /cvs/stx/stx/libbasic/Character.st,v 1.137 2009-08-17 22:07:57 cg Exp $'
 ! !