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OpenMusic Documentation




Absoluate Pathname

An absolute pathname, also referred to as an absolute path or a full path, is the location of a filesystem object – file, directory or link– relative to the root directory.


Abstraction is a procedure that permits to abstract a program, that is, a process, a patch, into a box that can then be used into another program. In other words, an abstraction box represents a patch in another patch and acts as a function.


A program or patch can be more or less complex, and comprise one or several components "layers", like a tree structure. Such structures consist of patches embedded into other patches. Processes embedded in higher-level programs are called abstractions.

Abstraction aims at using a program as a function within another program.

  • From a formal view, an abstraction results from the conversion of one or several elements of a program into variables .
  • Consequently, in practical terms, an abstraction must have at least one outlet to communicate with the external environment .

An argument represents a parameter upon which a function operates. For instance, the (om+ x y) function has two arguments : x and y.


An elementary item, number, symbol, string. An atom can be part of a list.

Break Point Function

A "break-point" function is a function defined by a finite number of points (x,y).



Elementary Lisp functions, allowing the access to one or more elements in a list.

Lisp fonctions are actually linked list. Lists are actually "conses" (or "pairs") made of a first element and a pointer to the rest (or "tail") of the list (another cons). These two parts of the list are accessed with the CAR and CDR functions, respectively.

Let the following list be : (A B C D).

CAR (A B C D) = A.

CDR (A B C D) = (B C D).

CDR (B) => NIL [this list has no CDR]

"CAR" and "CDR" are technical terms which originally refer to the way data is handled by the computer. CAR is the acronym of "Contents of the Address part of Register number". CDR is the acronym of "Contents of the Decrement part of Register number".

The rest of the functions below are built upon these two kernel accessors.

CADR (A B C D) = B. CADR means CAR of the CDR.

CDDR (A B C D) = (C D). CDDR means CDR of the CDR.

CADDR (A B C D) = C. CADDR means CAR of the CDDR.

NTHCDR (A B C D) = NTH CDR of the list – N must be specified as argument. NTHCDR 3 (A B C D) = (D).

And so on...


OM name of a chord sequence. By extension, a note sequence, since a single note can be considered a chord.


A category of objects sharing common properties – characteristics and behaviour. A class specifies the internal structure and behaviour of an object. In OM, it is represented in a patch by a factory box that can produce an instance of a class.

See also : Object, Instance

CLOS – Common Lisp Object System –

CLOS is an object-oriented programming protocol defined in the Common Lisp language specification. It is based on classes, instances of classes, generic functions and methods to be used in Lisp programs.

See also : Class, Function, Generic Function, Method, Instance.

Conditional Operators

Conditional operators execute an operation if one or more preconditions are fulfilled. If these conditions are not fulfilled, they can possibly execute another operation.

OM offers two conditional operators : omif and conditional , which operate according to the following paradigm : "IF A, THEN do B, ELSE do C".


In OM, a container is an object that contains a number of sub objects, including other containers as well. For instance, a chord-seq that contains chords, a chord that contains notes, a maquette that contains temporal objects, etc.

Contextual menu

A pop up menu that allows to choose actions to be performed upon an object.

Ctrl click or right click in an OM window or on one of its item.


Reducing the number of arguments of a lambda function by assigning values to some of them.



Corresponds to the "directory'' concept in many host file systems: the name of a group of related files (typically those belonging to a single user or project).


In Lisp, evaluating an expression amounts to interpreting and reducing its contents in order to return a result.

In OM, visual programs represent Lisp expressions and evaluating a box triggers the calculus that will determine the value of these expressions.

Any kind of box can be evaluated and return something. To evaluate a box, ⤷ Click and press v or Cmd click on an outlet.

Factory Box

A box used for creating an instance, or exemplar, of a given class within a visual program.

First Class Object

A first-class object is an entity which can be passed as a parameter to a function, returned from a function, or assigned into the variable of a program.


A  portion of code within a larger program, which performs a specific task. Operates upon 0 or more parameters and returns a value.

Functional Abstraction

A functional abstraction is a program whose some elements can become variables, via connections to the outside environment. Hence, this program must have inputs or outputs that can be connected to external variable elements. The resulting functional abstraction can then be embedded into other programs to be used as a functional component.


Generic Function

In object oriented programming, a generic function is a collection of methods – elementary specialized functions – with the same name and argument structure, but with arguments typed differently.

See also : Method

Global variable

An instance of OM object that has been saved in order to be used in other programs. Global variables are visible from the Library window and stored as .omi files in the Globals folder of the workspace.


An internal subdivision, that is, a list of proportions within a measure. A group can enclose a sub group. Basic examples are tuplets, groups of eighth, sixteenth notes. Groups of quarter, semibreves, whole notes or any other values are also admitted in rhythm trees.

For instance :

(? ((4//4 ( (2 ( 1 1)) (1 ( 1 (1 (1 1 1)))) (1 (1 1 1 1 1)) )))).

This one measure tree has one group – two quarter notes – , one group with a sub group – one eighth note and a sixteenth notes triplet, and a last group – a quintuplet.



An actual object created at runtime, out of a given class. In OM, more specifically, an object created when evaluating a factory box. An instance can be saved as a global variable.

SHIFT click on an outlet – especially the first outlet representing the self, the whole object – of a factory box to materialize an instance.


An instance is an exemplar of a class of objects. Instantiation is the process of creating an instance of a class using a factory box.

Internal Evaluation

Evaluation of a box by OM, triggered by a user evaluation, or by the internal evaluation of an upstream box connected to it.


The repetition of a process within a computer program.

See also : Recursion.


Iteration is the repetition of a process in order to apply it to a series of items.



A library is a set of tools, or framework, used by an application – like OM – to execute specific tasks.

Lisp Listener

A Lisp communication interface displaying results of computations, warnings or error messages, and where Lisp expressions – programs – can be evaluated.

Lisp Package

In Lisp, a package is a means to gather symbols, such as functions, variables or class names, within a same specific name space. You are always working in a "current" package, which can be changed with the command (in-package "my-package").

In orde to use items defined in other packages (unless these item's names are "exported" to the current package), it is generally necessary to type the package name (or "nickname"), separated by " : :", before the usual name ( Ex. : om : :om+ ).

The default package in OM is "OPENMUSIC" or "OM". The default package in Common Lisp is "CL-USER".


A finite ordered sequence of elements delineated by two parenthesis, where each element itself is an atom or a list.

See also : Atom.



A hybrid of visual program and sequencer, a programming unit provided with a time dimension, where musical material is organized in a time oriented structure.


A matrix is a rectangular array of m*n numbers, with m rows and n columns, such as :

1 2 3

4 5 6


An elementary function or part of a generic function defining rules for its behaviour depending on a type of argument. Defining a generic function amounts to defining at least one method.

For instance, the OM+ function is made of four methods : 1. number + list / 2. list + number / 3. number + number / 4. list + list


A midicent is a unit representing one cent of the usual MIDI pitch unit, that is, a half-tone. For instance, a C4 corresponds to 60 in MIDI, and to 6000 midicents, C4# to 61, i.e. 6100 midicents, and so on.


In computing, the modulo operation finds the remainder of division of one number by another. If two numbers, a and b , when divided by the same n divisor, have the same remainder, they are "equal modulo n ".

-> If remainder ( a  / n ) = remainder ( b / n ), a = b , modulo n .



Converts a note name or list of note names into corresponding midi cents values. The reference is the standard notation, where the medium C (6000 midicents) = C3.


The name of a group of files that can be thought of as the "same'' file


A thing provided with properties – characteristics and behaviour. An object is defined by a class and shares the same characteristics with other objects belonging to the same class.

An exemplar of a class.

For instance, the class of Note defines all possible notes by listing the characteristics and behaviors they can have. The object A4 is a particular note : it is an instance of the Class note, with particular versions of its characteristics. A note has a pitch. An A4 is a 440 Hz note.

See also : Class, Instance, Object Oriented Programming.


Temporal position of an object.

In a chord, each note can have a specific offset.

OM Function

A function that has been specifically designed for OpenMusic, and that doesn't belong to Lisp.

Omor, Omand

Omor and omand are boolean logical operators that stand for the "and" and "or" coordinating conjunctions.

  • A proposition that contains an "and" is true if all its elements are true.
  • A proposition that contains an "or" is true if at least one of its elements is true.

For instance, the following propositions are respectively true and false :

  • A : "Men are living creatures". B : "Cats are living creatures". "A and B" is true, and "A or B" is true.
  • A : "Men are human beings." B : "Cats are human beings". "A or B" is true, but "A and B" is not true.


  • the omand box returns "true" if all its inputs return "true". Otherwise, it returns "nil".
  • the omor box returns "true" if one of its inputs return "true". Otherwise, it returns "nil".



Contains functions or classes components belonging to a common category of programming items. Packages are provided at the installation of OM, but the can also be loaded dynamically or added by the user.


A package represents a category of programming tools that encloses related functions and classes. It can be organized in sub packages.

Parent Directory

A parent directory is the directory in which a given directory is located. In an absolute path, the parent directoy is the predecessor of the current directory.


A programming unit where objects and functions – boxes – are interconnected to build a musical algorithm, that is, a sequence of instructions. A patch can also be embedded as a box within another patch.

Persistent object/document, Persistence

A persistent object corresponds to a "real" file that is kept somewhere in the hard drive of the computer. Examples of persistent objects in OM are patches, maquettes, or global variables. The corresponding documents are kept in the Workspace folder. Conversely, a "non-persistent" object lays within a program but cannot be manipulated as an independent file.


The concept of predicate refers to a property, or to a relation between the terms of a proposition.

A predicates is a boolean operators : it is a function which tests for a condition involving its arguments. If the condition is fulfilled, the operator returns "true" or "false" – "yes" or "no".

In Lisp, "nil" means "false", and "t" means "true". As a convention, any non nil value is also interpreted as "true".

There are several types of predicates. Among these, algebraic predicates compare numbers, equality predicates test if two objects are identical, type predicates that test if an object belongs to a specific type, and so on.

In OM, predicates are often used as conditions for the execution of a program.


A predicate verifies the property of a thing or a relation between two things. It has two possible answers : "true", and "false", that is, "t", or "nil" in Lisp.



In computer science, recursion is the application of a function within its own definition. This method allows to solve complex problems.

In order no to "call itself" infinitely, a recursive function must include a termination condition . A termination condition is a necessary condition so that the function doesn't call itself.

Relative Pathname

A relative pathname tells the location of a filesystem object relative to the directory in which the user is currently working.

Rhythm Tree

A rhythm tree expresses a rhythmic structure as a list.

This list is made of :

  • a duration, or number of measures,

  • a list of measures.

Each measure is made of

  • a time signature

  • a list or proportions, or rhythmic values.

For instance : (1 (((4 4) (1 1 2))) is a rhythm of one measure, signature 4/4, with two quarter and one half note (proportions = 1/4 1/4 2/4 = 1/4 1/4 1/2).

The term of "tree" refers to a recusrive structure: each item in the proportions list can in turn be expressed as a duration with a list of subdivisions.

For instance the second beat in our measure could be subdivided as follows : ((4 4) (1 (1 (2 3)) 2)).



In object oriented programming, a slot represents and attribute of a class. For instance, the class "note" in OM has 4 slots : pitch, duration, velocity, and MIDI channel.


A characters chain between two inverted commas.


A subclass is derived from a preexisting class, by inheritance. In object-oriented programming, objects are defined by classes. New objects can be created from existing objects. As objects are defined by classes, classes can inherit other classes. Sub-classes inherit attributes and behavior of the pre-existing classes, or super-classes. Code is compartmentalized and reused by creating collections of attributes and behaviors called objects which can be based on previously created objects.

Subdivisions of the Whole Note

Memento :

= 1, = 2, = 4, = 8, = 16, = 32, = 64


Temporal object

In a maquette, any object provided with an explicit or computable duration, such as an audio file, a chord object or a patch.

See also : Maquette.


A TemporalBox refers to an object in a maquette : an instance, a patch, or another maquette.

User Evaluation

A user evaluation triggers one or more internal evaluation of the box and of possible upstream boxes connected to it.


OpenMusic's working environment. Each session starts with choosing a workspace, the equivalent of a desktop where programs are created and organized, and where items can be stored.

A propos...(c) Ircam - Centre PompidouRéalisé avec Scenari