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Tutorial 43: Creating a Generic Function II

A musical approach

Topics

Using musical classes as data types for methods

Key Modules Used

x-append, sort., remove-dup, Note, Chord

The Concept:

As we saw in the previous tutorial, a function may contain any number of methods determining its behavior. Each method corresponds to a set of data types at the function’s inputs, and is automatically called when these data types are present. Any class can be used as a data type, it turns out. In this tutorial we will add functionality to our myplus function, defined in the previous tutorial, allowing it to ‘add’ Chords and Notes by adding additional methods.

Adding New Methods

We will define the addition operation for the NOTE class as adding two notes to produce a diad. Two notes will form an interval. In order to do this we will again use classes from the Packages folder in the Workspace. This time, however, we will open the Music:Score package:

Open up myplus and select File->New Method. The usual method editor window comes up. This time, drag the Note class icon twice from the Packages folder. Notice these inputs have many outputs:

Each of these outputs refers to a slot of the class. They give us access not only to the _self_ output of the Note, but to its constituent slots _midic_ , _vel_ , _dur_ , and _chan_.

If we open the Note class in the Packages folder, we see these slots:

Notice that the _self_ slot is not shown- this is because it is always present most classes. (The Note icon could be taken to represent the _self_ slot, in fact. You also see extra slots that don’t appear in the graphic representation of the class when the class is used in the patch: _tie_ and _symb-info_. These slots are used when the Note becomes part of a larger object; we won’t need to manipulate them directly.

So, in order to combine the pitches of the two notes, we will create a list with x-append. We could simply pass this list to the output, but it would make more sense for myplus to return a musical object in this case, so we give the values to the _midic_ input of a Chord object, and pass the entire object to the output (via the _self_ output).

We may use our newly edited function:

Using two Notes, we connect them to myplus and get back a Chord:

Now let’s create a method for two Chord objects. This method will combine them into a single object, without any repretition of pitches, and will sort all notes from lowest to highest.

First, we create the new method and drag the Chord classes from the Packages folder to the inputs. We connect the _lmidic_ output of both to the x-append function, which combines the midics into a single list. Then we connect that to sort. (note the period at the end of the name) which will arrange them, by default, in ascending order. Next, they are passed to remove-dup, which, by default, removes duplicate elements from the list. Now we’re ready to put our filtered, sorted list of midics into the _lmidic_ input of a Chord object, and on to the output.

We can now use the new method: A Chord

and second Chord:

…are connected to myplus and the output passed to a third Chord object:

The resulting chord, viewed in order mode:

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