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From: "Ludovic Courtès" <ludo@gnu.org>
To: Ricardo Wurmus <rekado@elephly.net>
Cc: 34948@debbugs.gnu.org
Subject: [bug#34948] [PATCH 1/3] records: Allow thunked fields to refer to 'this-record'.
Date: Sat, 30 Mar 2019 11:37:48 +0100	[thread overview]
Message-ID: <877ecg641v.fsf@gnu.org> (raw)
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")

Hello!

I’ve 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 ‘this-package’ and it will refer to the closest
package in scope.  The good thing is that you can refer to
‘this-package’ from within, say, an <origin> field, and it will DTRT.

That also means you could have things such as:

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

… 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’s “implicit parameters”:

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

Ludo’.

  reply	other threads:[~2019-03-30 10:39 UTC|newest]

Thread overview: 12+ messages / expand[flat|nested]  mbox.gz  Atom feed  top
2019-03-22 17:21 [bug#34948] [PATCH 0/3] Turn 'essential-services' into an <operating-system> field Ludovic Courtès
2019-03-22 17:27 ` [bug#34948] [PATCH 1/3] records: Allow thunked fields to refer to 'this-record' Ludovic Courtès
2019-03-22 17:27   ` [bug#34948] [PATCH 2/3] accounts: Add default value for the 'home-directory' field of <user-account> Ludovic Courtès
2019-03-22 17:27   ` [bug#34948] [PATCH 3/3] system: Add 'essential-services' field to <operating-system> Ludovic Courtès
2019-03-25 20:42     ` Arun Isaac
2019-03-25 23:02       ` bug#34948: " Ludovic Courtès
2019-03-26  6:58         ` [bug#34948] " Arun Isaac
2019-03-22 21:53   ` [bug#34948] [PATCH 1/3] records: Allow thunked fields to refer to 'this-record' Ricardo Wurmus
2019-03-23 15:18     ` Ludovic Courtès
2019-03-23 16:05     ` Ludovic Courtès
2019-03-30 10:37       ` Ludovic Courtès [this message]
2019-03-30 14:20       ` Ludovic Courtès

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