[slime-devel] giving reasons for RPC aborts

[Helmut Eller]

* Taylor R Campbell [2007-06-29 19:13+0200] writes:

>    Date: Fri, 29 Jun 2007 13:54:31 +0200
>    From: Helmut Eller <heller at common-lisp.net>
>
>    I dislike this idea.  Why can't the function just return an error
>    indicator together with the error message if it can't complete
>    normally?  I think we shouldn't add an exception system for RPCs.
>    Tagged return values are easy to understand and good enough for the
>    job.
>
> Is it really better to extend N different callees of `slime-eval' and
> friends to accept a tagged result to distinguish OK responses from
> errors, when the RPC mechanism already has one?  All of the callers
> where it is possible for a user error to arise would have to be
> modified to expect a possible error response -- say, remote callers of
> SWANK:SET-PACKAGE when the package doesn't exist,
> SWANK:SWANK-TOGGLE-TRACE or a number of other similar operations when
> the function in question is not defined, SWANK:GET-REPL-RESULT when
> the result is unavailable, and so on.

The plan is to remove the mechanism.  Changing the caller together
with the callee is a small price to pay.

>    Also, dropping into the debugger seems to be the proper action to
>    take.  If SLIME doesn't handle the returned value it's obviously a
>    bug.  (And the bug will be fixed sooner if the debugger pops up.)
>
> Sorry, I'm a little unclear:  Do you mean that it is the proper action
> to take to drop into the debugger for the above examples, where there
> is a single uniquely best course of action (namely, for the user to do
> something else after being presented with an error message); or that
> all of the RPC interfaces where user errors are possible should be
> changed to support them, and that any callers that don't deal with the
> errors gracefully should drop into the debugger?

The callees where it makes sense should be changed, together with the
callers.  Dropping into the debugger is also OK.  Silently ignoring
bugs or errors is never OK.

Helmut.