Topics

Defenition of a generic function and how to create it with OpenMusic

Functions used

plus and omloop

Description

Since OpenMusic is an open environment, we fluently willencounter a wide variety of data types, such as lists, symbols, atoms etc... and many different objects (CHORD, VOICE, POLY, etc...). If we must apply on most of these a general function such as addition, one must define this function for each type of object. In CommonLisp, this function will be called a generic function. This function will have different methods. In this tutorial we will see how to create such a function and its methods.

Creating the generic function 'myplus'

• In order to create a generic function, one must first open a patch . It is then that 'New Generic Function' will be available in the 'File' menu.

• Choose 'New Generic Function'

• It is the n where a dialogue box will appear enabeling you to choose the name and icon of your function. You may also document your function in the 'Documentation' area.

• In order to change your icon, double click on the yellow icon. Then this window will appear:

The icons on the right side are standard OM icons. The ones on the left are the user's icons that the user may want to add. For this mater you will have to use a resorce editor such as ResEdit and add these icons in the 'WSPL.rsrc' file that you'll find in the current workspace folder (NOTE: please be carefull while using these editors. Always work with a copy !).

 

 

• After editing the dialogue and hitting the 'Ok' button, the function's editing window will appear.

• We will now edit our function as we have done in the other tutorials using extra inputs and outputs according to our function definition.

The main difference between functions that we have done uptill now (e.g tutorial 9 ) and a generic function is the type of our arguments. In a generic function we are editing methods who will apply to specific data types. In the editing window, whenever we add an extra input (in our example we will need two inputs) its type will be a universal one applying to any data type. (This type is the lisp 't' standing for true) .

Here we will start and define a method for integers. In order to apply this type, we must open the 'packages' folder on the workspace and drag from the 'kernel->lisp' subfolders the integer class onto our two extra inputs.

Now we will patch these two inputs to the lisp '+' function (this function takes as arguments only two integers).

 

• Our function is now available in the menu 'Functions' in the submenu 'user'

• This function will operate the sum of two integers and is equivalent to the lisp '+' function and to the following lisp expression:

(+ 5 3)

• Now let us add to this generic function a new method which will allow it to use the sum operation for an integer as a first argument and a list for the second one.

Once you drag the new function onto a patch, you must double click on it in order to add a new method and open its methods window

In this window will appear all available methods for this function. Here we still have one method and we can clearly notice the data types concerning its inputs.

To add a new method one must select in the 'File' menu 'New Method'

A new editing window will appear with extra buttons on its upper part (we will comment about these later in this tutorial). This will mean that we are editing a new method for our function.

 

We will again drag two new classes (integer and list) from the packages folder as we have already done for our first method.

If you double click on the omloop icon, you will notice that the integer will be added to each element of the list using listloop for the second argument (cf tutorial 14).

 

 

• We will also add two new methods for:
  • lists as first argument and integers as second argument (same operation as above, except tha t we will use enumeration for the first input).
  • lists for both arguments. There we will use enumeration for both as shown below

• Now our myplus method can deal with both data types (list and integers). We can examine its four methods in the method window if we double click on its icon

• Now that our generic function and its method are defined the user may find them in the workspace's folder in the folder 'user'

NOTE: If you want to use them in other workspaces, you must copy them in the 'user' folder of these ones.

• Since this method is equivalent to the om+ method we will edit extra methods dealing with music classes in tutorial 43