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[spec] Fix block values #609

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Nov 30, 2017
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[spec] Fix block values #609

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16 changes: 7 additions & 9 deletions document/core/exec/instructions.rst
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Expand Up @@ -964,24 +964,22 @@ Exiting :math:`\instr^\ast` with label :math:`L`

When the end of a block is reached without a jump or trap aborting it, then the following steps are performed.

1. Let :math:`n` be the arity of :math:`L`.
1. Let :math:`m` be the number of values on the top of the stack.
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I know what you mean by "values on top of the stack", but is that mentioned anywhere in the spec?

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The runtime section defines the stack. Although never defined explicitly, the spec mentions "the top of the stack" in various places. Do you think it might be too unclear?

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I think it's probably fine when it's just a few values. This case is perhaps a little less clear since you're only counting up from the label. That said, the formula below makes it explicit.


2. Assert: due to :ref:`validation <valid-instr-seq>`, there are :math:`n` values on the top of the stack.
2. Pop the values :math:`\val^m` from the stack.

3. Pop the results :math:`\val^n` from the stack.
3. Assert: due to :ref:`validation <valid-instr-seq>`, the label :math:`L` is now on the top of the stack.

4. Assert: due to :ref:`validation <valid-instr-seq>`, the label :math:`L` is now on the top of the stack.
4. Pop the label from the stack.

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

6. Push :math:`\val^n` back to the stack.

7. Jump to the position after the |END| of the :ref:`structured control instruction <syntax-instr-control>` associated with the label :math:`L`.
6. Jump to the position after the |END| of the :ref:`structured control instruction <syntax-instr-control>` associated with the label :math:`L`.

.. math::
~\\[-1ex]
\begin{array}{lcl@{\qquad}l}
\LABEL_n\{\instr^\ast\}~\val^n~\END &\stepto& \val^n
\LABEL_n\{\instr^\ast\}~\val^m~\END &\stepto& \val^m
\end{array}

.. note::
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