1 Exception Handling
2 ==================
3
4 Active Exceptions
5 =================
6
7 When an exception is raised, an exception instance is defined as the active
8 exception. This active exception remains in force until either a new exception
9 is raised in any handling of the exception, or upon exit of a handler where
10 the active exception has been caught (thus resetting the active exception).
11
12 NOTE: Currently, if classes are used with "raise" statements, no instantiation
13 NOTE: of such classes occurs. This should be remedied.
14
15 Instructions
16 ------------
17
18 StoreException records the current value reference using the exception
19 register.
20
21 LoadException obtains the current exception and puts it in the value register.
22
23 CheckException checks the current exception against a class referenced by the
24 current value.
25
26 ClearException resets the exception register.
27
28 Handlers
29 ========
30
31 An exception handler stack is defined such that when a try...except or
32 try...finally block is entered, a new handler is defined.
33
34 When an exception is raised, the program jumps to the most recently defined
35 handler. Inside the handler, the stack entry for the handler will be removed.
36
37 Depending on the nature of the handler and whether the exception is handled,
38 the program may jump to the next most recent handler, and so on.
39
40 If no handler is defined when an exception is raised or re-raised, the program
41 should terminate. This might be done by having a "handler #0" which explicitly
42 terminates the program.
43
44 Instructions
45 ------------
46
47 PushHandler(block) defines an active handler at the location indicated by the
48 given block.
49
50 PopHandler(n) removes the n topmost active handlers. A single handler is
51 typically removed when leaving a try block, but potentially more handlers are
52 removed when such a block is exited using a return statement.
