12.2.2 Internal music representation

When a music expression is parsed, it is converted into a set of Scheme music objects. The defining property of a music object is that it takes up time. Time is a rational number that measures the length of a piece of music in whole notes.

A music object has three kinds of types:

• music name: Each music expression has a name. For example, a note leads to a NoteEvent, and \simultaneous leads to a SimultaneousMusic. A list of all expressions available is in the Program reference manual, under Music expressions.
• ‘type’ or interface: Each music name has several ‘types’ or interfaces, for example, a note is an event, but it is also a note-event, a rhythmic-event, and a melodic-event. All classes of music are listed in the Program reference, under Music classes.
• C++ object: Each music object is represented by an object of the C++ class Music.

The actual information of a music expression is stored in properties. For example, a NoteEvent has pitch and duration properties that store the pitch and duration of that note. A list of all properties available is in the internals manual, under Music properties.

A compound music expression is a music object that contains other music objects in its properties. A list of objects can be stored in the elements property of a music object, or a single ‘child’

music object in the element object. For example, SequentialMusic has its children in elements, and GraceMusic has its single argument in element. The body of a repeat is stored in the element property of RepeatedMusic, and the alternatives in elements.