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Add prose for exiting a CAUGHTadm block. #227

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Add prose for exiting a CAUGHTadm block. #227

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25 changes: 20 additions & 5 deletions document/core/exec/instructions.rst
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Expand Up @@ -3039,17 +3039,32 @@ Throwing an exception with :ref:`tag address <syntax-tagaddr>` :math:`a`

.. _exec-caughtadm:

Holding a caught exception with |CAUGHTadm|
...........................................
Exiting a |CAUGHTadm|
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Exiting a |CAUGHTadm|
Exiting a catch clause |CAUGHTadm|

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Made PR #240 with this and the other changes requested.

.....................

When the |END| of a |CAUGHTadm|, is reached without a jump, exception, or trap, then the following steps are performed.
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When the |END| of a |CAUGHTadm|, is reached without a jump, exception, or trap, then the following steps are performed.
When the |END| of a catch clause |CAUGHTadm| is reached without a jump, exception, or trap, then the following steps are performed.


1. Let :math:`\val^\ast` be the values on the top of the stack.

2. Pop the values :math:`\val^\ast` from the stack.

3. Assert: due to :ref:`validation <valid-instr-seq>`, an administrative instruction :math:`\CAUGHTadm\{a~\val_0^\ast\}` is now on the top of the stack.

4. Pop the |CAUGHTadm| from the stack.
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4. Pop the |CAUGHTadm| from the stack.
4. Pop the catch clause |CAUGHTadm| from the stack.


5. Push :math:`\val^\ast` back to the stack.
Comment on lines +3047 to +3055
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Other similar sections ('Exiting an exception handler' and 'Exiting instr with label L') use val^m. Is there any reason we use val^* here? For example, our 'Exiting an exception handler' section's prose is:

Exiting an exception handler                                                     
............................                                                     

When the end of a :ref:`try <syntax-try>` instruction is reached without a jump, exception, or trap, then the following steps are performed.

1. Let :math:`m` be the number of values on the top of the stack.

2. Pop the values :math:`\val^m` from the stack.

3. Assert: due to :ref:`validation <valid-instr-seq>`, the handler :math:`H` is now on the top of the stack.

4. Pop the handler from the stack.

5. Push :math:`\val^m` back to the stack.

6. Jump to the position after the |END| of the administrative instruction associated with the handler :math:`H`.

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@aheejin "Exiting instr with label L" uses val^m because it's relevant to the rule, in that labels are of the form label_m. Since caught does not have such a subscript, I used *, and I think it should be the same for "Exiting an exception handler".
So I would be more inclined to change to val^* in "Exiting an exception handler" and leaving this val* here as it is, but I would go with whatever you prefer. WDYT?


6. Jump to the position after the |END| of the administrative instruction associated with the |CAUGHTadm| instruction.

.. todo::
Add prose describing the administrative |CAUGHTadm| execution step.

.. math::
\begin{array}{rcl}
\CAUGHTadm\{a~\val^n\}~\val^m~\END &\stepto& \val^m
\CAUGHTadm\{a~\val_0^\ast\}~\val^\ast~\END &\stepto& \val^\ast
\end{array}

.. note::
An exception can only be rethrown from the scope of the |CAUGHTadm| administrative instruction holding it, i.e., from the scope of the |CATCH| or |CATCHALL| block of a :ref:`try-catch <syntax-try-catch>` instruction that caught it. Upon exit from a |CAUGHTadm|, the exception it holds is discarded.


.. index:: ! call, function, function instance, label, frame

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