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Subject: [bug#34948] [PATCH 1/3] records: Allow thunked fields to refer to
	'this-record'.
Resent-Message-ID: <handler.34948.B34948.155394228213636@debbugs.gnu.org>
From: Ludovic =?UTF-8?Q?Court=C3=A8s?= <ludo@gnu.org>
References: <20190322172120.10974-1-ludo@gnu.org>
	<20190322172719.11199-1-ludo@gnu.org> <87y35660fw.fsf@elephly.net>
	<87a7hlzidl.fsf@gnu.org>
Date: Sat, 30 Mar 2019 11:37:48 +0100
In-Reply-To: <87a7hlzidl.fsf@gnu.org> ("Ludovic
	\=\?utf-8\?Q\?Court\=C3\=A8s\=22'\?\=
	\=\?utf-8\?Q\?s\?\= message of "Sat, 23 Mar 2019 17:05:10 +0100")
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To: Ricardo Wurmus <rekado@elephly.net>
Cc: 34948@debbugs.gnu.org

Hello!

I=E2=80=99ve extended this a bit with these commits:

  d8bead6c5d system: Define 'this-operating-system'.
  adb6462c4c packages: Define 'this-package' and 'this-origin'.
  d2be7e3c4b records: Support custom 'this' identifiers.

Now you can refer to =E2=80=98this-package=E2=80=99 and it will refer to th=
e closest
package in scope.  The good thing is that you can refer to
=E2=80=98this-package=E2=80=99 from within, say, an <origin> field, and it =
will DTRT.

That also means you could have things such as:

  (define-record-type* <origin>
    ;; =E2=80=A6
    (file-name origin-file-name (thunked)
               (default (string-append (package-name this-package)
                                       "-source"))))

=E2=80=A6 which is pretty fun when you think about it, since it allows you =
to
implicitly refer to the lexically surrounding package.

That reminds me of Scala=E2=80=99s =E2=80=9Cimplicit parameters=E2=80=9D:

  https://docs.scala-lang.org/tour/implicit-parameters.html

Ludo=E2=80=99.