Impromptu is a

Mac OS X macOS (; previously OS X and originally Mac OS X) is a Unix operating system developed and marketed by Apple Inc. since 2001. It is the primary operating system for Apple's Mac computers. Within the market of desktop and lapt ...

programming environment for live coding. Impromptu is built around the

Scheme A scheme is a systematic plan for the implementation of a certain idea. Scheme or schemer may refer to: Arts and entertainment * ''The Scheme'' (TV series), a BBC Scotland documentary series * The Scheme (band), an English pop band * ''The Schem ...

language, which is a member of the

Lisp A lisp is a speech impairment in which a person misarticulates sibilants (, , , , , , , ). These misarticulations often result in unclear speech. Types * A frontal lisp occurs when the tongue is placed anterior to the target. Interdental lispi ...

family of languages. The source code of its core has been opened as the Extempore project.

Description

The environment allows to make changes to a program at runtime, so variables and functions may be redefined and the changes take effect immediately. A programmer can also create and schedule code for future execution, as well as data events such as notes and graphics objects. Once an event is scheduled, execution continues. Looping is performed by using an idiom called "temporal recursion" which works by having a function asynchronously schedule a future call to itself as its final action. The library allows communicating with

Audio Units Audio Units (AU) are a system-level plug-in architecture provided by Core Audio in Apple's macOS and iOS operating systems. Audio Units are a set of application programming interface (API) services provided by the operating system to generat ...

for audio synthesis, and with graphics layers such as

QuickTime QuickTime is an extensible multimedia framework developed by Apple Inc., capable of handling various formats of digital video, picture, sound, panoramic images, and interactivity. Created in 1991, the latest Mac version, QuickTime X, is a ...

Quartz Quartz is a hard, crystalline mineral composed of silica ( silicon dioxide). The atoms are linked in a continuous framework of SiO4 silicon-oxygen tetrahedra, with each oxygen being shared between two tetrahedra, giving an overall chemical ...

Core Image Core Image is a pixel-accurate, near-realtime, non-destructive image processing technology in Mac OS X. Implemented as part of the QuartzCore framework of Mac OS X 10.4 and later, Core Image provides a plugin-based architecture for applying filt ...

OpenGL OpenGL (Open Graphics Library) is a cross-language, cross-platform application programming interface (API) for rendering 2D and 3D vector graphics. The API is typically used to interact with a graphics processing unit (GPU), to achieve ha ...

for video composition. Code written in

Objective-C Objective-C is a general-purpose, object-oriented programming language that adds Smalltalk-style messaging to the C programming language. Originally developed by Brad Cox and Tom Love in the early 1980s, it was selected by NeXT for its N ...

can be called from the editor, and also Objective-C frameworks can perform calls to the Scheme interpreter. Impromptu's Scheme interpreter was initially built from the TinyScheme 1.35 baseline, but it has been substantially modified since to better suit the live coding context. A real-time garbage collector, and

integration were added. Also, a new statically typed language called the ''Extempore Language'' has been integrated to the system. This language is syntactically Scheme-like, but semantically closer to C, and is designed for real-time sound synthesis and other computationally heavy tasks. It provides

type inference Type inference refers to the automatic detection of the type of an expression in a formal language. These include programming languages and mathematical type systems, but also natural languages in some branches of computer science and linguistics. ...

and is compiled to

machine language In computer programming, machine code is any low-level programming language, consisting of machine language instructions, which are used to control a computer's central processing unit (CPU). Each instruction causes the CPU to perform a ver ...

LLVM LLVM is a set of compiler and toolchain technologies that can be used to develop a front end for any programming language and a back end for any instruction set architecture. LLVM is designed around a language-independent intermediate repre ...

Sample performance

''A Study in Keith'' is a live coding performance in Impromptu by Andrew Sorensen. The first two minutes (1:56) are silent, while the performer writes the program that will produce the introduction of the piece. From then on, he modifies the code on the fly to evolve the composition.

Extempore

The core of Impromptu has been released as Extempore under a BSD style licence. It runs under both

Linux Linux ( or ) is a family of open-source Unix-like operating systems based on the Linux kernel, an operating system kernel first released on September 17, 1991, by Linus Torvalds. Linux is typically packaged as a Linux distribution, which i ...

and Mac OS X. It includes the Scheme interpreter, the Extempore Language compiler and the scheduler. The bindings to

Apple An apple is an edible fruit produced by an apple tree (''Malus domestica''). Apple trees are cultivated worldwide and are the most widely grown species in the genus '' Malus''. The tree originated in Central Asia, where its wild ances ...

libraries are absent, but the environment can interface with dynamic libraries.

References

Academic papers

* Sorensen, A (2010)
A Distributed Memory For Networked Livecoding Performance
International Computer Music Conference 2010, New York * Sorensen, A & Brown, A (2008)
A Computational Model For The Generation Of Orchestral Music In The Germanic Symphonic Tradition: A progress report
paper presented to the Australasian Computer Music Conference 2008, Sydney * Sorensen, A & Brown, A (2007)
aa-cell in Practice: An Approach to Musical Live Coding
paper presented to the International Computer Music Conference 2007, Copenhagen * Sorensen, A. (2005)
Impromptu: An interactive programming environment for composition and performance
a paper presented to the Australasian Computer Music Conference 2005, Brisbane: ACMA, pp. 149–153. (Note: Impromptu version discussed is obsolete) * Sorensen, A.

* Thor Magnusson,
Confessions of a Live Coder
, Proceedings of International Computer Music Conference, 2011.

Other sources

* Peter Kirn,
Thought and Performance, Live Coding Music, Explained to Anyone - Really
, Create Digital Music, 2011 * Mitchell Whitelaw,

, 2007

External links

* {{Official website Audio programming languages Live coding Articles containing video clips