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Re: exceptions


No secrets: 

  (with-handler ([P? A]) Body)

1. When an exception is raised, it carries along a structure. Call it S.

2. A with-handler construct stops an exception from doing anything 
   until it has tested S with P?. 

3. If P? is true of S, then evaluate (A S). 
   If P? is false, continue with the exception process .. keep 
   on raising it. 

As Shriram has pointed out, with-handlers actually allows you to specify a
whole bunch of P?-A pairs. 

-- Matthias