| paul@57 | 1 | Exception Handling
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| paul@232 | 2 | ==================
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| paul@232 | 3 |
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| paul@232 | 4 | Active Exceptions
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| paul@232 | 5 | =================
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| paul@232 | 6 |
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| paul@232 | 7 | When an exception is raised, an exception instance is defined as the active
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| paul@232 | 8 | exception. This active exception remains in force until either a new exception
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| paul@232 | 9 | is raised in any handling of the exception, or upon exit of a handler where
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| paul@232 | 10 | the active exception has been caught (thus resetting the active exception).
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| paul@232 | 11 |
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| paul@232 | 12 | Handlers
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| paul@232 | 13 | ========
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| paul@57 | 14 |
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| paul@109 | 15 | An exception handler stack is defined such that when a try...except or
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| paul@109 | 16 | try...finally block is entered, a new handler is defined.
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| paul@57 | 17 |
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| paul@109 | 18 | When an exception is raised, the program jumps to the most recently defined
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| paul@109 | 19 | handler. Inside the handler, the stack entry for the handler will be removed.
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| paul@57 | 20 |
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| paul@109 | 21 | Depending on the nature of the handler and whether the exception is handled,
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| paul@109 | 22 | the program may jump to the next most recent handler, and so on.
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| paul@57 | 23 |
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| paul@109 | 24 | If no handler is defined when an exception is raised or re-raised, the program
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| paul@109 | 25 | should terminate. This might be done by having a "handler #0" which explicitly
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| paul@109 | 26 | terminates the program.
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| paul@232 | 27 |
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| paul@232 | 28 | Instructions
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| paul@232 | 29 | ------------
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| paul@232 | 30 |
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| paul@232 | 31 | PushHandler(block) defines an active handler at the location indicated by the
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| paul@232 | 32 | given block.
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| paul@232 | 33 |
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| paul@232 | 34 | PopHandler removes the active handler at or after the location indicated by
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| paul@232 | 35 | the previously given block.
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