Re: Enable truncation of exception output

[Ludovic Courtès]

Hello!

Andy Wingo <address@hidden> skribis:

> On Fri 03 Feb 2017 14:40, Daniel Llorens <address@hidden> writes:
>
>> The patch to master (ice-9 boot-9) lets you override the (format) used
>> internally by the exception printers. Then I rewrite the format string
>> in user code, see below. It's a bit hacky, maybe someone has a better
>> solution.
>>
>> See also the other patch I've posted to the list to support arrays in
>> (truncated-print). The patches are independent, but they make each
>> other useful so to speak.
>
> I have a crazy idea :)  What about, we just let (ice-9 format) be
> "format" ?  Right now loading (ice-9 format) does a set! to format, as
> you know, overriding the core binding.  This is unnecessary and
> complicated.  I see that using (ice-9 format) only adds 50 KB to the
> 2828-KB baseline of private dirty memory.  Then we can use :@y
> directly in the format strings and we can avoid all the monkeypatching.
>
> There are only a couple instances of calls to scm_simple_format in
> libguile and they can be replaced, so we don't have C bootstrapping
> concerns.  Guile users calling scm_simple_format would do a pthread_once
> load to the "format" binding in the root module.  In boot-9, we start
> with a simple boot definition (for boot-time errors) then replace it
> with (module-ref (resolve-interface '(ice-9 format) 'format)) at the
> end.
>
> Maybe Ludovic has a thought here :)

I’d be in favor of something more conservative, notably because
‘simple-format’ remains faster than ‘format’:

  1. Remove ‘set!’ in (ice-9 format), which has always been a bad idea.
     -Wformat behaves as if this ‘set!’ wasn’t in place (that is, it
     warns you if you’re using “extended” functionality but haven’t
     explicitly imported (ice-9 format)), so I suspect little code will
     break.

     Then (ice-9 format) can #:replace (format) instead of #:export.

  2. For exception printers, use some autoload magic, just like we do
     for the debugger.

How does that sound?  I believe this should work no?

Ludo’.