Subject: [PATCH v2 5/5] records: Add MATCH-RECORD-LAMBDA.

From: "(" <[email-masked]>
Date: Fri, 28 Apr 2023 20:19:05 +0100

* guix/records.scm (match-record-lambda): New syntax.
* tests/records.scm ("match-record-lambda"): New test.
---
 .dir-locals.el    |  1 +
 guix/records.scm  | 15 ++++++++++++++-
 tests/records.scm | 12 ++++++++++++
 3 files changed, 27 insertions(+), 1 deletion(-)

diff --git a/.dir-locals.el b/.dir-locals.el
index 3ffd25ee94..d79b5c9d7e 100644
--- a/.dir-locals.el
+++ b/.dir-locals.el
@@ -71,6 +71,7 @@
    (eval . (put 'lambda* 'scheme-indent-function 1))
    (eval . (put 'substitute* 'scheme-indent-function 1))
    (eval . (put 'match-record 'scheme-indent-function 3))
+   (eval . (put 'match-record-lambda 'scheme-indent-function 2))
 
    ;; TODO: Contribute these to Emacs' scheme-mode.
    (eval . (put 'let-keywords 'scheme-indent-function 3))
diff --git a/guix/records.scm b/guix/records.scm
index 041eb2f297..504a023e87 100644
--- a/guix/records.scm
+++ b/guix/records.scm
@@ -31,7 +31,8 @@ (define-module (guix records)
             alist->record
             object->fields
             recutils->alist
-            match-record))
+            match-record
+            match-record-lambda))
 
 ;;; Commentary:
 ;;;
@@ -642,4 +643,16 @@ (define-syntax match-record
              (match-record-inner #,s record type (fields ...) body ...)
              (throw 'wrong-type-arg record))))))
 
+(define-syntax match-record-lambda
+  (lambda (s)
+    "Return a procedure accepting a single record of the given TYPE for which each
+FIELD will be bound to its FIELD name within the returned procedure.  A syntax error
+is raised if an unknown field is queried."
+    (syntax-case s ()
+      ((_ type (field ...) body ...)
+       #`(lambda (record)
+           (if (eq? (struct-vtable record) type)
+               (match-record-inner #,s record type (field ...) body ...)
+               (throw 'wrong-type-arg record)))))))
+
 ;;; records.scm ends here
diff --git a/tests/records.scm b/tests/records.scm
index 4f0aeb3903..8ee306bddc 100644
--- a/tests/records.scm
+++ b/tests/records.scm
@@ -590,4 +590,16 @@ (define-record-type* <with-thunked> with-thunked make-with-thunked
       (match-record rec <with-thunked> (normal thunked)
         (list normal thunked)))))
 
+(test-equal "match-record-lambda"
+  '("thing: foo" "thing: bar")
+  (begin
+    (define-record-type* <with-text> with-text make-with-text
+      with-text?
+      (text with-text-text))
+
+    (map (match-record-lambda <with-text> (text)
+           (string-append "thing: " text))
+         (list (with-text (text "foo"))
+               (with-text (text "bar"))))))
+
 (test-end)
-- 
2.39.2