"Like the C++ code that executes \revert, but without type
checking. "
- (define (revert-member alist entry new)
- "Return ALIST, with ENTRY removed. ALIST is not modified, instead
+ (define (entry-count alist entry-key)
+ "Count the number of entries in alist with a key of
+ENTRY-KEY."
+ (cond
+ ((null? alist) 0)
+ ((equal? (caar alist) entry-key)
+ (+ 1 (entry-count (cdr alist) entry-key)))
+ (else (entry-count (cdr alist) entry-key))))
+
+ (define (revert-member alist entry-key)
+ "Return ALIST, with the first entry having a key of
+ENTRY-KEY removed. ALIST is not modified, instead
a fresh copy of the list-head is made."
(cond
- ((null? alist) new)
- ((equal? (car alist) entry) (revert-member (cdr alist) entry new))
- (else (revert-member (cdr alist) entry (cons (car alist) new)))))
-
- (ly:context-set-property!
- context property
- (revert-member (ly:context-property context property) setting '())))
+ ((null? alist) '())
+ ((equal? (caar alist) entry-key) (cdr alist))
+ (else (cons (car alist)
+ (revert-member (cdr alist) entry-key)))))
+
+ ;; body of revert-property-setting
+ (let ((current-value (ly:context-property context property)))
+ (if (> (entry-count current-value setting) 1)
+ (ly:context-set-property!
+ context
+ property
+ (revert-member current-value setting)))))
(define-public (override-time-signature-setting time-signature setting . rest)
"Override the time signature settings for the context in @var{rest},