Attached is another variant of the extensible exceptions idea, it improves on the previous designs in a couple of ways: there's only one catch & throw, regardless of what type you're throwing or catching. There is an extensible hierarchy of exceptions, and you can catch and re-throw subclasses of exceptions.
So this design contains a dynamically-typed extensible hierarchy, but
it's fairly lightweight. Adding a new leaf exception type requires 3
lines + 1 line for each superclass (just 1 line for a top level leaf, as
before). Adding a new node requires about 10 lines + 1 line for each
superclass, msotly boilerplate.
Perhaps the type class hackers can do better than this!
Cheers,
Simon
Exception-2.hs
Description: Exception-2.hs
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