+(define (recent-enough? bar-number alteration-def laziness)
+ (or (number? alteration-def)
+ (equal? laziness #t)
+ (<= bar-number (+ (cadr alteration-def) laziness))))
+
+(define (accidental-invalid? alteration-def)
+ "Checks an alteration entry for being invalid.
+
+Non-key alterations are invalidated when tying into the next bar or
+when there is a clef change, since neither repetition nor cancellation
+can be omitted when the same note occurs again.
+
+Returns @code{#f} or the reason for the invalidation, a symbol."
+ (let* ((def (if (pair? alteration-def)
+ (car alteration-def)
+ alteration-def)))
+ (and (symbol? def) def)))
+
+(define (extract-alteration alteration-def)
+ (cond ((number? alteration-def)
+ alteration-def)
+ ((pair? alteration-def)
+ (car alteration-def))
+ (else 0)))
+
+(define (check-pitch-against-signature context pitch barnum laziness octaveness)
+ "Checks the need for an accidental and a @q{restore} accidental against
+@code{localKeySignature}. The @var{laziness} is the number of measures
+for which reminder accidentals are used (i.e., if @var{laziness} is zero,
+only cancel accidentals in the same measure; if @var{laziness} is three,
+we cancel accidentals up to three measures after they first appear.
+@var{octaveness} is either @code{'same-octave} or @code{'any-octave} and
+specifies whether accidentals should be canceled in different octaves."
+ (let* ((ignore-octave (cond ((equal? octaveness 'any-octave) #t)
+ ((equal? octaveness 'same-octave) #f)
+ (else
+ (ly:warning (_ "Unknown octaveness type: ~S ") octaveness)
+ (ly:warning (_ "Defaulting to 'any-octave."))
+ #t)))
+ (key-sig (ly:context-property context 'keySignature))
+ (local-key-sig (ly:context-property context 'localKeySignature))
+ (notename (ly:pitch-notename pitch))
+ (octave (ly:pitch-octave pitch))
+ (pitch-handle (cons octave notename))
+ (need-restore #f)
+ (need-accidental #f)
+ (previous-alteration #f)
+ (from-other-octaves #f)
+ (from-same-octave (assoc-get pitch-handle local-key-sig))
+ (from-key-sig (or (assoc-get notename local-key-sig)
+
+ ;; If no key signature match is found from localKeySignature, we may have a custom
+ ;; type with octave-specific entries of the form ((octave . pitch) alteration)
+ ;; instead of (pitch . alteration). Since this type cannot coexist with entries in
+ ;; localKeySignature, try extracting from keySignature instead.
+ (assoc-get pitch-handle key-sig))))
+
+ ;; loop through localKeySignature to search for a notename match from other octaves
+ (let loop ((l local-key-sig))
+ (if (pair? l)
+ (let ((entry (car l)))
+ (if (and (pair? (car entry))
+ (= (cdar entry) notename))
+ (set! from-other-octaves (cdr entry))
+ (loop (cdr l))))))
+
+ ;; find previous alteration-def for comparison with pitch
+ (cond
+ ;; from same octave?
+ ((and (not ignore-octave)
+ from-same-octave
+ (recent-enough? barnum from-same-octave laziness))
+ (set! previous-alteration from-same-octave))
+
+ ;; from any octave?
+ ((and ignore-octave
+ from-other-octaves
+ (recent-enough? barnum from-other-octaves laziness))
+ (set! previous-alteration from-other-octaves))
+
+ ;; not recent enough, extract from key signature/local key signature
+ (from-key-sig
+ (set! previous-alteration from-key-sig)))
+
+ (if (accidental-invalid? previous-alteration)
+ (set! need-accidental #t)
+
+ (let* ((prev-alt (extract-alteration previous-alteration))
+ (this-alt (ly:pitch-alteration pitch)))
+
+ (if (not (= this-alt prev-alt))
+ (begin
+ (set! need-accidental #t)
+ (if (and (not (= this-alt 0))
+ (and (< (abs this-alt) (abs prev-alt))
+ (> (* prev-alt this-alt) 0)))
+ (set! need-restore #t))))))
+
+ (cons need-restore need-accidental)))
+
+(define-public ((make-accidental-rule octaveness laziness) context pitch barnum measurepos)
+ "Create an accidental rule that makes its decision based on the octave of
+the note and a laziness value.
+
+@var{octaveness} is either @code{'same-octave} or @code{'any-octave} and
+defines whether the rule should respond to accidental changes in other
+octaves than the current. @code{'same-octave} is the normal way to typeset
+accidentals -- an accidental is made if the alteration is different from the
+last active pitch in the same octave. @code{'any-octave} looks at the last
+active pitch in any octave.
+
+@var{laziness} states over how many bars an accidental should be remembered.
+@code{0}@tie{}is the default -- accidental lasts over 0@tie{}bar lines, that
+is, to the end of current measure. A positive integer means that the
+accidental lasts over that many bar lines. @w{@code{-1}} is `forget
+immediately', that is, only look at key signature. @code{#t} is `forever'."
+
+ (check-pitch-against-signature context pitch barnum laziness octaveness))
+
+(define (key-entry-notename entry)
+ "Return the pitch of an entry in localKeySignature. The entry is either of the form
+ '(notename . alter) or '((octave . notename) . (alter barnum . measurepos))."
+ (if (number? (car entry))
+ (car entry)
+ (cdar entry)))
+
+(define (key-entry-octave entry)
+ "Return the octave of an entry in localKeySignature (or #f if the entry does not have
+ an octave)."
+ (and (pair? (car entry)) (caar entry)))
+
+(define (key-entry-bar-number entry)
+ "Return the bar number of an entry in localKeySignature (or #f if the entry does not
+ have a bar number)."
+ (and (pair? (car entry)) (caddr entry)))
+
+(define (key-entry-measure-position entry)
+ "Return the measure position of an entry in localKeySignature (or #f if the entry does
+ not have a measure position)."
+ (and (pair? (car entry)) (cdddr entry)))
+
+(define (key-entry-alteration entry)
+ "Return the alteration of an entry in localKeySignature.
+
+For convenience, returns @code{0} if entry is @code{#f}."
+ (if entry
+ (if (number? (car entry))
+ (cdr entry)
+ (cadr entry))
+ 0))
+
+(define-public (find-pitch-entry keysig pitch accept-global accept-local)
+ "Return the first entry in @var{keysig} that matches @var{pitch}.
+@var{accept-global} states whether key signature entries should be included.
+@var{accept-local} states whether local accidentals should be included.
+If no matching entry is found, @var{#f} is returned."
+ (and (pair? keysig)
+ (let* ((entry (car keysig))
+ (entryoct (key-entry-octave entry))
+ (entrynn (key-entry-notename entry))
+ (oct (ly:pitch-octave pitch))
+ (nn (ly:pitch-notename pitch)))
+ (if (and (equal? nn entrynn)
+ (or (and accept-global (not entryoct))
+ (and accept-local (equal? oct entryoct))))
+ entry
+ (find-pitch-entry (cdr keysig) pitch accept-global accept-local)))))
+
+(define-public (neo-modern-accidental-rule context pitch barnum measurepos)
+ "An accidental rule that typesets an accidental if it differs from the
+key signature @emph{and} does not directly follow a note on the same
+staff line. This rule should not be used alone because it does neither
+look at bar lines nor different accidentals at the same note name."
+ (let* ((keysig (ly:context-property context 'localKeySignature))
+ (entry (find-pitch-entry keysig pitch #t #t)))
+ (if (not entry)
+ (cons #f #f)
+ (let* ((global-entry (find-pitch-entry keysig pitch #t #f))
+ (key-acc (key-entry-alteration global-entry))
+ (acc (ly:pitch-alteration pitch))
+ (entrymp (key-entry-measure-position entry))
+ (entrybn (key-entry-bar-number entry)))
+ (cons #f (not (or (equal? acc key-acc)
+ (and (equal? entrybn barnum) (equal? entrymp measurepos)))))))))
+
+(define-public (teaching-accidental-rule context pitch barnum measurepos)
+ "An accidental rule that typesets a cautionary accidental if it is
+included in the key signature @emph{and} does not directly follow a note
+on the same staff line."
+ (let* ((keysig (ly:context-property context 'localKeySignature))
+ (entry (find-pitch-entry keysig pitch #t #t)))
+ (if (not entry)
+ (cons #f #f)
+ (let* ((global-entry (find-pitch-entry keysig pitch #f #f))
+ (key-acc (key-entry-alteration global-entry))
+ (acc (ly:pitch-alteration pitch))
+ (entrymp (key-entry-measure-position entry))
+ (entrybn (key-entry-bar-number entry)))
+ (cons #f (not (or (equal? acc key-acc)
+ (and (equal? entrybn barnum) (equal? entrymp measurepos)))))))))
+