[web-devel] xml-types IsString instance for Name causes crashes

Aristid Breitkreuz aristidb at googlemail.com
Tue Jun 7 17:55:21 CEST 2011

I think Ghc does allow catching pure exceptions.
Am 07.06.2011 17:53 schrieb "Yitzchak Gale" <gale at sefer.org>:
> I wrote:
>>>> I noticed when looking at the IsString instance
>>>> for Name: it can introduce crashes into a program if someone
>>>> accidentally puts a '{' at the beginning of a Name string.
>> Or accidentally omits the '}' in Clark notation.
>> The way xml-types is now, it cannot be used in an
>> environment where code is not allowed to introduce
>> any additional risk of crashes. That is quite common in
>> commercial development.
> John Millikin wrote:
>> The code won't ever *crash*, it will merely throw an exception,
>> which can be caught...
>> Second, GHC's IsString feature is not enabled by default...
>> Third, the IsString instance is largely for convenience...
> Sorry, I guess I really wasn't making myself clear.
> I never raised any doubts about it being *possible*, or even
> easy, to write safe code using the xml-types library as it
> is now.
> In a large-scale software development environment, one way
> that risk is evaluated is by counting the number of ways that it
> is *possible* for a library to cause a crash. And yes, in this
> context raising an asynchronous exception that knocks your
> program all the way out to some last-chance exception
> handler in the outer IO layer counts as a crash.
> Since the whole idea of xml-types is for it to be a
> unifying standard, I'd like to see it usable in that kind
> of environment, too.
> In addition, I have already pointed out that semantically
> it doesn't make sense for a fromString implementation
> to return _|_. And it is easy to make a small change
> to the current implementation to avoid that.
> So let me turn the question around. Is there a compelling
> reason why, in some use case, the fromString must
> return _|_, rather than returning some text that will allow
> the application to handle the situation itself?
> Thanks,
> Yitz
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