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Semantics of AsynchronousExceptions

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Conventions and Notations

Primitive IO actions are considered “values” for the purely functional part of thesemantics (>>=, putChar, block etc)

Evaluation contexts are assumed to be maximal

• F  = [.] | F >>= M | catch F H

• E  = F  | F [ block E ] | F [ unblock E ]

Threads can be:

• Stuck: ( … )•

• Runnable: ( … )o

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IO Primitives

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Threads and Exceptions

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Basic Transitions

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Asynchronous Exceptions

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Higher-level Operators

onException :: IO a -> IO b -> IO aonException io what

= io `catch` (\e -> what >> throw (e :: SomeException))

finally :: IO a -> IO b -> IO aa `finally` sequel = block $ do

r <- unblock a `onException` sequelsequelreturn r 

try :: Exception e => IO a -> IO (Either e a)try a = (a >>= (return . Right)) `catch` (return . Left)