[bug#56898] [PATCH 04/13] read-print: Introduce <blank> parent class of <comment>.

["Ludovic Courtès" <ludo@gnu.org>]

* guix/read-print.scm (<blank>, blank?): New record type.
(<comment>): Redefine using the record interface.
(read-with-comments, pretty-print-with-comments): Change some uses of
'comment?' to 'blank?'.
* guix/scripts/style.scm (simplify-inputs)[simplify-expressions]: Use
'blank?' instead of 'comment?'.
---
 guix/read-print.scm    | 37 ++++++++++++++++++++++++++-----------
 guix/scripts/style.scm |  2 +-
 2 files changed, 27 insertions(+), 12 deletions(-)

diff --git a/guix/read-print.scm b/guix/read-print.scm
index 5281878504..732d0dc1f8 100644
--- a/guix/read-print.scm
+++ b/guix/read-print.scm
@@ -22,13 +22,14 @@ (define-module (guix read-print)
   #:use-module (ice-9 rdelim)
   #:use-module (ice-9 vlist)
   #:use-module (srfi srfi-1)
-  #:use-module (srfi srfi-9)
   #:use-module (srfi srfi-34)
   #:use-module (srfi srfi-35)
   #:export (pretty-print-with-comments
             read-with-comments
             object->string*
 
+            blank?
+
             comment
             comment?
             comment->string
@@ -47,12 +48,26 @@ (define-module (guix read-print)
 ;;; Comment-preserving reader.
 ;;;
 
-;; A comment.
-(define-record-type <comment>
-  (string->comment str margin?)
-  comment?
-  (str     comment->string)
-  (margin? comment-margin?))
+(define <blank>
+  ;; The parent class for "blanks".
+  (make-record-type '<blank> '()
+                    (lambda (obj port)
+                      (format port "#<blank ~a>"
+                              (number->string (object-address obj) 16)))
+                    #:extensible? #t))
+
+(define blank? (record-predicate <blank>))
+
+(define <comment>
+  ;; Comments.
+  (make-record-type '<comment> '(str margin?)
+                    #:parent <blank>
+                    #:extensible? #f))
+
+(define comment?        (record-predicate <comment>))
+(define string->comment (record-type-constructor <comment>))
+(define comment->string (record-accessor <comment> 'str))
+(define comment-margin? (record-accessor <comment> 'margin?))
 
 (define* (comment str #:optional margin?)
   "Return a new comment made from STR.  When MARGIN? is true, return a margin
@@ -66,7 +81,7 @@ (define* (comment str #:optional margin?)
   (string->comment str margin?))
 
 (define (read-with-comments port)
-  "Like 'read', but include <comment> objects when they're encountered."
+  "Like 'read', but include <blank> objects when they're encountered."
   ;; Note: Instead of implementing this functionality in 'read' proper, which
   ;; is the best approach long-term, this code is a layer on top of 'read',
   ;; such that we don't have to rely on a specific Guile version.
@@ -99,7 +114,7 @@ (define (reverse/dot lst)
               (let/ec return
                 (let liip ((lst '()))
                   (liip (cons (loop (match lst
-                                      (((? comment?) . _) #t)
+                                      (((? blank?) . _) #t)
                                       (_ #f))
                                     (lambda ()
                                       (return (reverse/dot lst))))
@@ -327,7 +342,7 @@ (define newline?
                       (and (keyword? item)
                            (not (eq? item #:allow-other-keys))))
                   (not first?) (not delimited?)
-                  (not (comment? item))))
+                  (not (blank? item))))
 
            (when newline?
              (newline port)
@@ -335,7 +350,7 @@ (define newline?
            (let ((column (if newline? indent column)))
              (print tail
                     (keyword? item)      ;keep #:key value next to one another
-                    (comment? item)
+                    (blank? item)
                     (loop indent column
                           (or newline? delimited?)
                           context
diff --git a/guix/scripts/style.scm b/guix/scripts/style.scm
index e2530e80c0..5c0ecc0896 100644
--- a/guix/scripts/style.scm
+++ b/guix/scripts/style.scm
@@ -108,7 +108,7 @@ (define (simplify-expressions exp inputs return)
                (exp exp)
                (inputs inputs))
       (match exp
-        (((? comment? head) . rest)
+        (((? blank? head) . rest)
          (loop (cons head result) rest inputs))
         ((head . rest)
          (match inputs
-- 
2.37.1