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
On Tue, Apr 11, 2006 at 01:24:07PM +0100, Simon Marlow wrote:
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.
I made the catch and throw separate so the decision as to whether to include imprecice exceptions and extensible extensions can be made independently. that and throw x /= ioError x ioError x >> return () -> IO _|_ (only _|_ when IO action executed) throw x >> return () -> _|_ ioError x `seq` () -> () throw x `seq` () -> _|_ John -- John Meacham - ⑆repetae.net⑆john⑈
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John Meacham -
Simon Marlow