From mboxrd@z Thu Jan  1 00:00:00 1970
From: ludo@gnu.org (Ludovic =?utf-8?Q?Court=C3=A8s?=)
Subject: Re: New =?utf-8?Q?=E2=80=98--list-generations=E2=80=99?= and
	=?utf-8?Q?=E2=80=98--delete-generations=E2=80=99?= options
Date: Thu, 12 Sep 2013 14:26:16 +0200
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In-Reply-To: <87wqmmxutb.fsf@karetnikov.org> (Nikita Karetnikov's message of
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To: Nikita Karetnikov <nikita@karetnikov.org>
Cc: guix-devel@gnu.org

Nikita Karetnikov <nikita@karetnikov.org> skribis:

>> Probably this can reduce to a big =E2=80=98cond=E2=80=99, which would be=
 even more
>> readable:
>
>>   (cond ((maybe-integer)
>>          =3D>
>>          list)
>>         ((string-match "^([0-9]+)\\.\\.([0-9]+)$" str)
>>          =3D>
>>          (lambda (match)
>>            ...))
>>         ...)
>
> Are you sure?  I haven=E2=80=99t found a way to make =E2=80=98cond=E2=80=
=99 as readable as =E2=80=98or=E2=80=99.

Yes, it makes it easier to enumerate all the cases, and to reason about it.

For instance, in =E2=80=98string->generations=E2=80=99, getting rid of =E2=
=80=98maybe-*-range=E2=80=99
and instead inlining the =E2=80=98string-match=E2=80=99 calls in =E2=80=98c=
ond=E2=80=99 would greatly
clarify things IMO:

  (cond ((maybe-integer) ...)
        ((maybe-comma-separated-integers) ...)
        ((string-match p1 x) =3D> ...)
        ((string-match p2 x) =3D> ...)
        ((string-match p3 x) =3D> ...)
        (else #f))

> I=E2=80=99m attaching a sketchy version.  If you don=E2=80=99t see any pr=
oblems, I=E2=80=99ll
> try to integrate this code into =E2=80=98package.scm=E2=80=99.

I=E2=80=99d prefer clearer case analysis as shown above.

Thanks,
Ludo=E2=80=99.