1.1 --- a/docs/exceptions.txt Sun Dec 08 18:00:53 2013 +0100
1.2 +++ /dev/null Thu Jan 01 00:00:00 1970 +0000
1.3 @@ -1,52 +0,0 @@
1.4 -Exception Handling
1.5 -==================
1.6 -
1.7 -Active Exceptions
1.8 -=================
1.9 -
1.10 -When an exception is raised, an exception instance is defined as the active
1.11 -exception. This active exception remains in force until either a new exception
1.12 -is raised in any handling of the exception, or upon exit of a handler where
1.13 -the active exception has been caught (thus resetting the active exception).
1.14 -
1.15 -NOTE: Currently, if classes are used with "raise" statements, no instantiation
1.16 -NOTE: of such classes occurs. This should be remedied.
1.17 -
1.18 -Instructions
1.19 -------------
1.20 -
1.21 -StoreException records the current value reference using the exception
1.22 -register.
1.23 -
1.24 -LoadException obtains the current exception and puts it in the value register.
1.25 -
1.26 -CheckException checks the current exception against a class referenced by the
1.27 -current value.
1.28 -
1.29 -ClearException resets the exception register.
1.30 -
1.31 -Handlers
1.32 -========
1.33 -
1.34 -An exception handler stack is defined such that when a try...except or
1.35 -try...finally block is entered, a new handler is defined.
1.36 -
1.37 -When an exception is raised, the program jumps to the most recently defined
1.38 -handler. Inside the handler, the stack entry for the handler will be removed.
1.39 -
1.40 -Depending on the nature of the handler and whether the exception is handled,
1.41 -the program may jump to the next most recent handler, and so on.
1.42 -
1.43 -If no handler is defined when an exception is raised or re-raised, the program
1.44 -should terminate. This might be done by having a "handler #0" which explicitly
1.45 -terminates the program.
1.46 -
1.47 -Instructions
1.48 -------------
1.49 -
1.50 -PushHandler(block) defines an active handler at the location indicated by the
1.51 -given block.
1.52 -
1.53 -PopHandler(n) removes the n topmost active handlers. A single handler is
1.54 -typically removed when leaving a try block, but potentially more handlers are
1.55 -removed when such a block is exited using a return statement.
2.1 --- a/docs/lowlevel.txt Sun Dec 08 18:00:53 2013 +0100
2.2 +++ b/docs/lowlevel.txt Sun Dec 08 18:04:32 2013 +0100
2.3 @@ -11,6 +11,7 @@
2.4 * Instantiation
2.5 * List and tuple representations
2.6 * Instruction evaluation model
2.7 + * Exception handling
2.8
2.9 Objects and Structures
2.10 ======================
2.11 @@ -363,3 +364,51 @@
2.12 Using the approach where arguments are treated like attributes in some kind of
2.13 structure, we could choose to allocate frames in places other than a stack.
2.14 This would produce something somewhat similar to a plain tuple object.
2.15 +
2.16 +Exception Handling
2.17 +==================
2.18 +
2.19 +Active Exceptions
2.20 +-----------------
2.21 +
2.22 +When an exception is raised, an exception instance is defined as the active
2.23 +exception. This active exception remains in force until either a new exception
2.24 +is raised in any handling of the exception, or upon exit of a handler where
2.25 +the active exception has been caught (thus resetting the active exception).
2.26 +
2.27 +The following operations can be employed to achieve this:
2.28 +
2.29 +StoreException records the current value reference using the exception
2.30 +register.
2.31 +
2.32 +LoadException obtains the current exception and puts it in the value register.
2.33 +
2.34 +CheckException checks the current exception against a class referenced by the
2.35 +current value.
2.36 +
2.37 +ClearException resets the exception register.
2.38 +
2.39 +Handlers
2.40 +--------
2.41 +
2.42 +An exception handler stack is defined such that when a try...except or
2.43 +try...finally block is entered, a new handler is defined.
2.44 +
2.45 +When an exception is raised, the program jumps to the most recently defined
2.46 +handler. Inside the handler, the stack entry for the handler will be removed.
2.47 +
2.48 +Depending on the nature of the handler and whether the exception is handled,
2.49 +the program may jump to the next most recent handler, and so on.
2.50 +
2.51 +If no handler is defined when an exception is raised or re-raised, the program
2.52 +should terminate. This might be done by having a "handler #0" which explicitly
2.53 +terminates the program.
2.54 +
2.55 +The following operations can be employed to achieve this:
2.56 +
2.57 +PushHandler(block) defines an active handler at the location indicated by the
2.58 +given block.
2.59 +
2.60 +PopHandler(n) removes the n topmost active handlers. A single handler is
2.61 +typically removed when leaving a try block, but potentially more handlers are
2.62 +removed when such a block is exited using a return statement.
