comparison classes.lisp @ 1:cbb5b478307e

Initial import of classes.lisp and default-methods.lisp from David.

darcs-hash:20061016144427-aa3d6-93919f5153445ade41eb753434da6f3c838c155a.gz

+;; basic musical object classes
+
+(defclass composition ()
+  ())
+
+(defclass event ()
+  ())
+
+(defclass pitched-event (event)
+  ())
+
+;; pitch-related classes
+
+(defclass pitch ()
+  ())
+
+(defclass chromatic-pitch (pitch)
+  ())
+
+(defclass diatonic-pitch (pitch)
+  ())
+
+(defclass frequency (pitch)
+  ())
+
+(defclass interval ()
+  ())
+
+;; time-related classes
+
+(defclass moment ()
+  ())
+
+(defclass duration ()
+  ())
+
+;; Some conditions we might want to be able to signal
+
+(define-condition undefined-action (condition)
+  ;; This condition would apply to an attempt to perform a meaningless
+  ;; operation on an object. This may, initially, include things that
+  ;; are a pain to implement but should really be used when it's
+  ;; genuinely unclear what an operation means in the given
+  ;; context. In such cases, a condition handler might be the best
+  ;; approach anyway.
+  ((operation :initarg :operation
+	      :reader undefined-action-operation)
+   (datatype :initarg :datatype
+	     :reader undefined-action-datatype))
+  (:report (lambda (condition stream)
+	     (format stream "The consequence of performing ~A on and object of type ~A is undefined"
+		     (undefined-action-operation condition)
+		     (undefined-action-datatype condition)))
+
+(define-condition insufficient-information (condition)
+  ;; It should be possible to construct genuinely minimal musical
+  ;; structures. When the information in these is insufficient to
+  ;; answer a query, this condition should be raised.
+  ((operation :initarg :operation
+	      :reader insufficient-information-operation)
+   (datatype :initarg :datatype
+	     :reader insufficient-information-datatype))
+  (:report (lambda (condition stream)
+	     (format stream "The ~A object does not contain enough information to perform ~A"
+		     (insufficient-information-datatype condition)
+		     (insufficient-information-operation condition)))
+
+