GNU bug report logs - #21829
guix import hackage failures

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Message #50 received at 21829 <at> debbugs.gnu.org (full text, mbox):

From: ludo <at> gnu.org (Ludovic Courtès)
To: Federico Beffa <beffa <at> ieee.org>
Cc: 21829 <at> debbugs.gnu.org, Paul van der Walt <paul <at> denknerd.org>
Subject: Re: guix import hackage failures
Date: Thu, 26 Nov 2015 09:46:00 +0100

Federico Beffa <beffa <at> ieee.org> skribis:

> On Wed, Nov 25, 2015 at 10:45 PM, Ludovic Courtès <ludo <at> gnu.org> wrote:
>> Federico Beffa <beffa <at> ieee.org> skribis:
>
> [...]
>
>>>>> +      ;; indentation based block recognition.
>>>>> +      (begin (unread-char #\newline port) (read-char port) 0)
>>>>
>>>> Isn’t this equivalent to: 0 ?
>>>
>>> No. This is because at the start of a new line we check if and how
>>> many indentation blocks have ended. If the last line doesn't terminate
>>> this check is no done.
>>
>> More generally, it looks like:
>>
>>   (begin (do-effect!) (undo-effect!) val)
>>
>> which I thought reduces to:
>>
>>   val
>
> Since we are doing IO, there are side effects. The key difference is
> the result of '(port-column port)' and that triggers what I mentioned.

Oooh, I see, thanks for explaining!  Then what about a comment like:

  Read a newline from PORT to reset its ‘port-column’, as expected by
  the indentation-based block recognition code.

I think it would be helpful for those like me who are hard of hearing.
;-)

Ludo’.

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