On Wed, Jul 09, 2008 at 04:17:25PM +0200, Henning Thielemann wrote: ...
There is also another unintended application: Escaping from loops or deep recursions, maybe even returning a result by an exception. Actually, in order to define the interaction of abort mechanisms like RETURN in a PROCEDURE or EXIT in LOOP, the Modula-3 designers defined RETURN and EXIT in terms of exceptions (although they suggested to implement them more efficiently). These abuses of exceptions made Niklaus Wirth, the inventor of Pascal, fear, that exceptions bring back a GOTO into structured programming languages.
Incidentally, the Haskell standard libraries (although not the report) also implement exitWith in terms of an exception. Personally, I think this is a great idea, as I'd rather not deal with two separate mechanisms for cleaning up in unexpected cases (i.e. bugs or exceptions or being passed a function that calls exitWith). Having one exception-handling mechanism allows for modular programming, e.g. I can write a function of type doSomethingThatMightRequireFreeingResources :: ... -> IO a -> IO a rather than requiring some sort of weird trickery to figure out all the possible ways that my argument might possible fail to return so that I can free whatever resources I need to free. David