[m-dev.] try syntax

[Peter Ross]

On Thu, Jan 22, 2009 at 5:10 PM, Peter Wang <novalazy at gmail.com> wrote:
> Hi,
>
> Catching exceptions is too cumbersome.  I think we should have built in
> syntax, e.g. (adjust accordingly if the parser is too dumb)
>
I agree, I guess the reason we don't have it as I'm pretty sure the
compiler doesn't use a lot of exception handling code, unlike the
servers that we write.

>    try [io(!IO)] (
>        f(X, Y, Z, !IO)
>    ) then (
>        on_success(X, Y, Z)     % outputs in scope
>    ) else (
>        on_failure
>    ) catch [_ : exc1] (        % zero or more catch blocks
>        on_catch_exc1
>    ) catch [E] (
>        rethrow(exception(E))
>    ) finally (                 % optional
>        cleanup
>    )
>
> io(!IO) selects try_io.
> store(!S) selects try_store.
> all(Solutions) selects try_all.
> Otherwise use try.
>
> We'd implement it by doing a tranformation to call the underlying
> predicates in the exception module.  The following assumes no `finally'
> block.
>
>    try_io(
>        (pred({X0, Y0, Z0}::out, !.IO::di, !:IO::uo) is det :-
>            f(X0, Y0, Z0, !IO)
>        ), TryResult, !IO),
>    (
>        TryResult = succeeded({X, Y, Z}),
>        on_success(X, Y, Z)
>    ;
>        TryResult = failed,
>        on_failure
>    ;
>        TryResult = exception(E0),
>        ( univ_to_type(E0, _ : exc1) ->
>            on_catch_exc1
>        ; univ_to_type(E0, E) ->
>            rethrow(exception(E))
>        )
>    )
>
What would be the behavour if you don't have a catch block that
succeeds?  In other words what goes in the last else in the above
transformation?
--------------------------------------------------------------------------
mercury-developers mailing list
Post messages to:       mercury-developers at csse.unimelb.edu.au
Administrative Queries: owner-mercury-developers at csse.unimelb.edu.au
Subscriptions:          mercury-developers-request at csse.unimelb.edu.au
--------------------------------------------------------------------------