From: Ricardo Wurmus <rekado@elephly.net>
To: "Ludovic Courtès" <ludo@gnu.org>
Cc: 34948@debbugs.gnu.org
Subject: [bug#34948] [PATCH 1/3] records: Allow thunked fields to refer to 'this-record'.
Date: Fri, 22 Mar 2019 22:53:07 +0100 [thread overview]
Message-ID: <87y35660fw.fsf@elephly.net> (raw)
In-Reply-To: <20190322172719.11199-1-ludo@gnu.org>
Ludovic Courtès <ludo@gnu.org> writes:
> * guix/records.scm (this-record): New syntax parameter.
> (make-syntactic-constructor)[wrap-field-value]: When F is thunked,
> return a one-argument lambda instead of a thunk, and parameterize
> THIS-RECORD.
So the value of the thunked field is no longer strictly a thunk?
I’m having difficulties understanding how this works. Why does the
“thunked field” now require an argument (“x”)?
We use the syntax parameter “this-record” to introduce a new binding
with this name in the context of the “value” of the field. The
parameter value is … hard to make out. How does the syntax-case macro
in the following syntax-parameterize expression evaluate to the record
itself? Would #,x not be sufficient to refer to the argument of the
field accessor?
> (define (wrap-field-value f value)
> (cond ((thunked-field? f)
> - #`(lambda () #,value))
> + #`(lambda (x)
> + (syntax-parameterize ((this-record
> + (lambda (s)
> + (syntax-case s ()
> + (id
> + (identifier? #'id)
> + #'x)))))
--
Ricardo
next prev parent reply other threads:[~2019-03-22 22:03 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 ` Ricardo Wurmus [this message]
2019-03-23 15:18 ` [bug#34948] [PATCH 1/3] records: Allow thunked fields to refer to 'this-record' Ludovic Courtès
2019-03-23 16:05 ` Ludovic Courtès
2019-03-30 10:37 ` Ludovic Courtès
2019-03-30 14:20 ` Ludovic Courtès
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