[racket-dev] Changing the default error display handler to use

I wonder whether we could collect the information on these
parameters and nail down their interaction constraints somehow.
(This could be a research project.) 




On Mar 13, 2014, at 9:34 PM, Matthew Flatt wrote:

> At Wed, 12 Mar 2014 18:05:03 -0700, Eric Dobson wrote:
>> A common issue I have is that the default error handler does not
>> display error message's exn:srcloc if it has it [...]
>> 
>> Is this reasonable to add to the default error handler, and if so do
>> people have suggestions on the format?
> 
> You mean the default error display handler, right?
> 
> I think this change may be worth a try, but there are many
> exception-generating, exception-handling, and exception-printing
> parameters to worry about, both in their interactions and how they're
> currently used.
> 
> For example, does DrRacket use the default error display handler? If
> so, it will start printing source locations that it's already showing a
> different way, and I think that's not what you intend. Or some other
> program harness might be worse off if the default display error handler
> starts showing source locations. Then again, the whole point is that
> you want to change the display of errors. Trying to change some things
> and not changes others --- and having enough extension points to
> accommodate certain combinations of changes and non-changes --- is why
> the existing set of parameters and handlers is complex. I will not be
> surprised if we end up with yet another parameter here.
> 
> If the change makes sense, probably the handler should not print the
> first returned source location for `exn:fail:read`, `exn:fail:syntax`,
> and `exn:fail:contract:variable` exceptions --- because that location
> is supposed to be built into the error-message text, unless the
> `error-print-source-location` parameter has a false value. Awkward, I
> know; see the previous paragraph.
> 
> The right format is likely to print an extra "<field>: <detail>",
> similar to the way that the default error display handler prints
> context lines (if the `error-context-display-depth` parameter is not
> 0). I imagine that the source-location lines should precede the context
> lines, but follow the exception's error message.
> 
> _________________________
>  Racket Developers list:
>  http://lists.racket-lang.org/dev