GNU bug report logs - #54652
[PATCH 1/2] guix: Only check the object type once in the MATCH-RECORD expansion.

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Message #5 received at submit <at> debbugs.gnu.org (full text, mbox):

From: Attila Lendvai <attila <at> lendvai.name>
To: guix-patches <at> gnu.org
Cc: Attila Lendvai <attila <at> lendvai.name>
Subject: [PATCH 1/2] guix: Only check the object type once in the MATCH-RECORD
 expansion.
Date: Thu, 31 Mar 2022 14:46:57 +0200

* guix/records.scm (match-record/fields): New macro.
(match-record): Only check the object type once in the expansion.
---
 guix/records.scm | 18 +++++++++++++-----
 1 file changed, 13 insertions(+), 5 deletions(-)

diff --git a/guix/records.scm b/guix/records.scm
index ed94c83dac..e311086d73 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -535,17 +535,25 @@ (define (recutils->alist port)
               (else
                (error "unmatched line" line))))))))
 
+(define-syntax match-record/fields
+  (syntax-rules ()
+    ((_ record type (field fields ...) body ...)
+     (let ((field ((record-accessor type 'field) record)))
+       ;; TODO compute indices and report wrong-field-name errors at
+       ;;      expansion time
+       ;; TODO support thunked and delayed fields
+       (match-record/fields record type (fields ...) body ...)))
+    ((_ record type () body ...)
+     (begin body ...))))
+
 (define-syntax match-record
   (syntax-rules ()
     "Bind each FIELD of a RECORD of the given TYPE to it's FIELD name.
 The current implementation does not support thunked and delayed fields."
     ((_ record type (field fields ...) body ...)
      (if (eq? (struct-vtable record) type)
-         ;; TODO compute indices and report wrong-field-name errors at
-         ;;      expansion time
-         ;; TODO support thunked and delayed fields
-         (let ((field ((record-accessor type 'field) record)))
-           (match-record record type (fields ...) body ...))
+         ;; So that we only test the type once.
+         (match-record/fields record type (field fields ...) body ...)
          (throw 'wrong-type-arg record)))
     ((_ record type () body ...)
      (begin body ...))))
-- 
2.34.0

Message #8 received at 54652 <at> debbugs.gnu.org (full text, mbox):

From: Attila Lendvai <attila <at> lendvai.name>
To: 54652 <at> debbugs.gnu.org
Cc: Attila Lendvai <attila <at> lendvai.name>
Subject: [PATCH 2/2] guix: MATCH-RECORD supports (FIELD-NAME VARIABLE-NAME)
 forms.
Date: Thu, 31 Mar 2022 14:52:31 +0200

E.g. (match-record obj <type> (field1 (field2 var-name)) ...)

* guix/records.scm (match-record/fields): Implement it.
---

a real world example i was facing: a field name is the same
as an object constructor, and thus shadows it in a
match-record form, unless a different variable name is chosen.

 guix/records.scm | 7 +++++--
 1 file changed, 5 insertions(+), 2 deletions(-)

diff --git a/guix/records.scm b/guix/records.scm
index e311086d73..492ab2aed6 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -537,12 +537,15 @@ (define (recutils->alist port)
 
 (define-syntax match-record/fields
   (syntax-rules ()
-    ((_ record type (field fields ...) body ...)
-     (let ((field ((record-accessor type 'field) record)))
+    ((_ record type ((field-name variable-name) fields ...) body ...)
+     (let ((variable-name ((record-accessor type 'field-name) record)))
        ;; TODO compute indices and report wrong-field-name errors at
        ;;      expansion time
        ;; TODO support thunked and delayed fields
        (match-record/fields record type (fields ...) body ...)))
+    ((_ record type (field fields ...) body ...)
+     ;; Channel it back into the canonical form above.
+     (match-record/fields record type ((field field) fields ...) body ...))
     ((_ record type () body ...)
      (begin body ...))))
 
-- 
2.34.0

Message #11 received at 54652 <at> debbugs.gnu.org (full text, mbox):

From: Attila Lendvai <attila <at> lendvai.name>
To: "54652 <at> debbugs.gnu.org" <54652 <at> debbugs.gnu.org>
Subject: (No Subject)
Date: Thu, 30 Jun 2022 13:56:13 +0000

one questionable thing: if fields is the empty list, then it skips entirely the runtime assert that checks the record type.

Message #16 received at 54652-close <at> debbugs.gnu.org (full text, mbox):

From: Attila Lendvai <attila <at> lendvai.name>
To: "54652-close <at> debbugs.gnu.org" <54652-close <at> debbugs.gnu.org>
Subject: (No Subject)
Date: Sun, 20 Nov 2022 14:18:11 +0000

closing, it was superseded by #59390

https://issues.guix.gnu.org/59390

-- 
• attila lendvai
• PGP: 963F 5D5F 45C7 DFCD 0A39
--
“Personal dishonesty is not needed to produce a dishonest business plan or research proposal. Wishful thinking suffices.”
	— John McCarthy (1927–2011), father of Lisp

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