+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; measure counter
+
+(define (measure-counter-stencil grob)
+ "Print a number for a measure count. The number is centered using
+the extents of @code{BreakAlignment} grobs associated with the left and
+right bounds of a @code{MeasureCounter} spanner. Broken measures are
+numbered in parentheses."
+ (let* ((num (markup (number->string (ly:grob-property grob 'count-from))))
+ (orig (ly:grob-original grob))
+ (siblings (ly:spanner-broken-into orig)) ; have we been split?
+ (num
+ (if (or (null? siblings)
+ (eq? grob (car siblings)))
+ num
+ (make-parenthesize-markup num)))
+ (num (grob-interpret-markup grob num))
+ (num (ly:stencil-aligned-to num X (ly:grob-property grob 'self-alignment-X)))
+ (left-bound (ly:spanner-bound grob LEFT))
+ (right-bound (ly:spanner-bound grob RIGHT))
+ (elts-L (ly:grob-array->list (ly:grob-object left-bound 'elements)))
+ (elts-R (ly:grob-array->list (ly:grob-object right-bound 'elements)))
+ (break-alignment-L
+ (filter
+ (lambda (elt) (grob::has-interface elt 'break-alignment-interface))
+ elts-L))
+ (break-alignment-R
+ (filter
+ (lambda (elt) (grob::has-interface elt 'break-alignment-interface))
+ elts-R))
+ (refp (ly:grob-system grob))
+ (break-alignment-L-ext (ly:grob-extent (car break-alignment-L) refp X))
+ (break-alignment-R-ext (ly:grob-extent (car break-alignment-R) refp X))
+ (num
+ (ly:stencil-translate-axis
+ num
+ (+ (interval-length break-alignment-L-ext)
+ (* 0.5
+ (- (car break-alignment-R-ext)
+ (cdr break-alignment-L-ext))))
+ X)))
+ num))
+
+;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;;
+;; make-engraver helper macro
+
+(defmacro-public make-engraver forms
+ "Helper macro for creating Scheme engravers.
+
+The usual form for an engraver is an association list (or alist)
+mapping symbols to either anonymous functions or to another such
+alist.
+
+@code{make-engraver} accepts forms where the first element is either
+an argument list starting with the respective symbol, followed by the
+function body (comparable to the way @code{define} is used for
+defining functions), or a single symbol followed by subordinate forms
+in the same manner. You can also just make an alist pair
+literally (the @samp{car} is quoted automatically) as long as the
+unevaluated @samp{cdr} is not a pair. This is useful if you already
+have defined your engraver functions separately.
+
+Symbols mapping to a function would be @code{initialize},
+@code{start-translation-timestep}, @code{process-music},
+@code{process-acknowledged}, @code{stop-translation-timestep}, and
+@code{finalize}. Symbols mapping to another alist specified in the
+same manner are @code{listeners} with the subordinate symbols being
+event classes, and @code{acknowledgers} and @code{end-acknowledgers}
+with the subordinate symbols being interfaces."
+ (let loop ((forms forms))
+ (if (or (null? forms) (pair? forms))
+ `(list
+ ,@(map (lambda (form)
+ (if (pair? (car form))
+ `(cons ',(caar form) (lambda ,(cdar form) ,@(cdr form)))
+ `(cons ',(car form) ,(loop (cdr form)))))
+ forms))
+ forms)))