David Farber writes:
 > 
 > today's puzzle is:
 > 
 >     Dictionary new
 >         at: (Set with: 1) put: 'is';
 >         at: (Set new add: 1; yourself) ifAbsent: ['isnot']
 > 
 > why does this little snippet *sometimes* answer 'is' and *sometimes* answers
 > 'isnot'?

Because Set reimplements #= but not #hash -- the classic one.  (The
Dictionary, searching for a key which is #= but not hash-equal to the
stored one, sometimes hits the right bucket but more often misses).

--Vassili

-- 
Vassili Bykov        vassili at objectpeople.com
The Object People    http://www.objectpeople.com
+1(613)225-8812
 "Any sufficiently complicated C or Fortran program contains an ad hoc
  informally-specified bug-ridden slow implementation of half of Common Lisp."
     -- Greenspun's Tenth Rule of Programming