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Re: EOF as datum
From: |
Pierre Lairez |
Subject: |
Re: EOF as datum |
Date: |
Sat, 2 Jul 2016 11:22:33 +0200 |
User-agent: |
Mozilla/5.0 (X11; Linux x86_64; rv:38.0) Gecko/20100101 Thunderbird/38.8.0 |
No, forget what I just wrote, this is obvious.
Pierre
On 02/07/2016 04:39, Mark H Weaver wrote:
> Hi,
>
> Pierre Lairez <address@hidden> writes:
>
>> I understand why we cannot use (eof-object) in a “case” statement. For
>> example, this will not run as it is meant:
>> (case (get-char port)
>> (((eof-object)) ...)
>> (else ...))
>>
>> Is is possible to define something like #eof that will be datum and make
>> the following work as expected?
>> (case (get-char port)
>> ((#eof) ...)
>> (else ...))
> We cannot make a 'read'able datum that is an eof object, because of the
> API of 'read'. When 'read' returns an eof object, that means that the
> end of file has been reached, and that's how existing callers of 'read'
> will interpret such a result.
>
> I would suggest using (ice-9 match) instead, e.g.:
>
> (match (get-char port)
> ((? eof-object?) 'eof)
> ((or #\a #\b) 'a-or-b)
> (#\c 'c)
> (char 'other-character))
>
> See section 7.7 (Pattern Matching) in the Guile manual.
> Does that work for you?
>
> Regards,
> Mark
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