Effect cases in switch

[Jan Lahoda]

On 13. 12. 23 13:49, forax at univ-mlv.fr wrote:

[snip]
>
>             Exception cases have the obvious dominance order with
>             other exception cases (the
>             same one used to validate order of `catch` clauses in
>             `try-catch`), and do not
>             participate in dominance ordering with non-exceptional
>             cases.  It is a
>             compile-time error if an exception case specifies an
>             exception type that cannot
>             be thrown by the selector expression, or a type that does
>             not extend
>             `Throwable`.  For clarity, exception cases should probably
>             come after all other
>             non-exceptional cases.
>
>             When evaluating a `switch` statement or expression, the
>             selector expression is
>             evaluated.  If evaluation of the selector expression
>             throws an exception, and
>             one of the exception cases in the `switch` matches the
>             exception, then control
>             is transferred to the first exception case matching the
>             exception.  If no
>             exception case matches the exception, then the switch
>             completes abruptly with
>             that same exception. 
>
>
>         I don't want to be the guy implementing this :)
>
>
>     Good news, Jan has volunteered to be that guy :)
>
>
> Are you sure you do not want a VM guy too ?


FWIW, we already run in the "try-catch with values on stack" problem in 
the case of a try-catch inside a switch expression. The current solution 
is to stash the stack to locals (which I suspect is similar to what you 
did in your case). It is not very pretty, but I think we can start with 
this and see if it poses problems in practice.


(I am a bit more concerned about the switch-with-case-throws used as a 
conditional e.g. in an if - that may be tricky, as the code needs to 
have some particular shape. I think we have some ideas on how to 
implement that in the compiler, but didn't try them yet.)


Jan

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