(cdr break-alignment-L-ext))))
X)))
num))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; The following are used by the \offset function
+
+(define (find-value-to-offset prop self alist)
+ "Return the first value of the property @var{prop} in the property
+alist @var{alist} -- after having found @var{self}. If @var{self} is
+not found, return the first value of @var{prop}."
+ (let ((segment (member (cons prop self) alist)))
+ (if (not segment)
+ (assoc-get prop alist)
+ (assoc-get prop (cdr segment)))))
+
+(define (offset-multiple-types arg offsets)
+ "Displace @var{arg} by @var{offsets} if @var{arg} is a number, a
+number pair, or a list of number pairs. If @var{offsets} is an empty
+list or if there is a type-mismatch, @var{arg} will be returned."
+ (cond
+ ((and (number? arg) (number? offsets))
+ (+ arg offsets))
+ ((and (number-pair? arg)
+ (or (number? offsets)
+ (number-pair? offsets)))
+ (coord-translate arg offsets))
+ ((and (number-pair-list? arg) (number-pair-list? offsets))
+ (map
+ (lambda (x y) (coord-translate x y))
+ arg offsets))
+ (else arg)))
+
+(define-public (offsetter property offsets)
+ "Apply @var{offsets} to the default values of @var{property} of @var{grob}.
+Offsets are restricted to immutable properties and values of type @code{number},
+@code{number-pair}, or @code{number-pair-list}."
+ (define (self grob)
+ (let* ((immutable (ly:grob-basic-properties grob))
+ ; We need to search the basic-properties alist for our property to
+ ; obtain values to offset. Our search is complicated by the fact that
+ ; calling the music function `offset' as an override conses a pair to
+ ; the head of the alist. This pair must be discounted. The closure it
+ ; contains is named `self' so it can be easily recognized. If `offset'
+ ; is called as a tweak, the basic-property alist is unaffected.
+ (target (find-value-to-offset property self immutable))
+ ; if target is a procedure, we need to apply it to our grob to calculate
+ ; values to offset.
+ (vals
+ (if (procedure? target)
+ (target grob)
+ target))
+ (can-type-be-offset?
+ (or (number? vals)
+ (number-pair? vals)
+ (number-pair-list? vals))))
+
+ (if can-type-be-offset?
+ ; '(+inf.0 . -inf.0) would offset to itself. This will be confusing to a
+ ; user unaware of the default value of the property, so issue a warning.
+ (if (equal? empty-interval vals)
+ (ly:warning "default '~a of ~a is ~a and can't be offset"
+ property grob vals)
+ (let* ((orig (ly:grob-original grob))
+ (siblings
+ (if (ly:spanner? grob)
+ (ly:spanner-broken-into orig)
+ '()))
+ (total-found (length siblings))
+ ; Since there is some flexibility in input syntax,
+ ; structure of `offsets' is normalized.
+ (offsets
+ (if (or (not (pair? offsets))
+ (number-pair? offsets)
+ (and (number-pair-list? offsets)
+ (number-pair-list? vals)))
+ (list offsets)
+ offsets)))
+
+ (define (helper sibs offs)
+ ; apply offsets to the siblings of broken spanners
+ (if (pair? offs)
+ (if (eq? (car sibs) grob)
+ (offset-multiple-types vals (car offs))
+ (helper (cdr sibs) (cdr offs)))
+ vals))
+
+ (if (>= total-found 2)
+ (helper siblings offsets)
+ (offset-multiple-types vals (car offsets)))))
+
+ (begin
+ (ly:warning "the property '~a of ~a cannot be offset" property grob)
+ vals))))
+ ; return the closure named `self'
+ self)