Re: [Scheme-reports] valid implementation of call-with-input-file?

[Andy Wingo <wingo@x>]

Hi,

On Tue 21 Aug 2012 04:36, Alex Shinn <alexshinn@x> writes:

>> I want them both, but given a choice I would rather have a useful
>> call-with-input-file (etc) than raise-continuable, in the small r7rs.
>
> As Alaric points out, with call/cc people can still
> write their own raise-continuable.

I believe I responded to this adequately in my reply to Alaric.  I think
this is fine and great & stuff.  Non-local exits that do not use the
exception mechanism would still keep the file open, and that's super.

> More generally, an exception does not mean control
> won't return to the body.  For example, if amb is used
> anywhere inside the dynamic extent of a c-w-i-f, then
> the next amb-fail will return there, even if called inside
> or after an external exception handler.

Exceptions are a conventional form of nonlocal exit.  You can of course
use other non-conventional means like amb or general call/cc.  But the
expectation should be that if you throw an exception, associated cleanup
handlers get run, from the dynamic extent of the throw on out to the
catch.

> `exception-protect' is useful but is only an 80% solution.
> It is therefore not appropriate for call-with-input/output-file.
> We can provide `exception-protect' and possibly other
> approaches in WG2, explore more options in the future,
> and let users choose which is most appropriate for their
> individual uses of c-w-i-f.

This is ridiculous.  The same argument would support not closing the
file after a normal exit from the c-w-i-f procedure.

Andy
-- 
http://wingolog.org/

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