From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: [PATCH] Add 'guix hash'.
Date: Wed, 10 Apr 2013 13:54:30 +0200
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In-Reply-To: <8738uy7gim.fsf@karetnikov.org> (Nikita Karetnikov's message of
	"Wed, 10 Apr 2013 15:48:49 +0400")
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To: Nikita Karetnikov <nikita@karetnikov.org>
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Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> Ah, TOCTTOU, right.
>
>> You could do:
>
>>   (let ((hash (catch 'system-error
>>                 (lambda ()
>>                   (call-with-input-file ...))
>>                 (lambda args
>>                   (leave (_ "error ..." (strerror (system-error-errno ar=
gs))))))))
>>     ...)
>
> Here is what I did (I'll remove "guix hash" when we have "warning"):
>
>       (match args
>         ((file)
>          (catch 'system-error
>            (lambda ()
>              (format #t "~a~%"
>                      (call-with-input-file file
>                        (compose fmt sha256 get-bytevector-all))))
>            (lambda args
>              (leave (_ "~a: ~a~%")
>                     "guix hash" (strerror (system-error-errno args))))))
>         (_
>          (leave (_ "~a: wrong number of arguments~%")
>                 "guix hash")))))

Looks good.

> I guess that "wrong number of arguments" can be handled by
> (lambda args ...).  Still, the above feels much safer.

Not sure what you mean, but the above snippet is OK.

Ludo=E2=80=99.