A+ (programming language)

A+ is a high-level, interactive, interpreted array programming language designed for numerically intensive applications, especially those found in financial applications.

A+
Paradigm	Array
Designed by	Arthur Whitney
Developer	Morgan Stanley
First appeared	1988; 37 years ago (1988)
Stable release	4.22-1 / March 27, 2008; 17 years ago (2008-03-27)
Typing discipline	Dynamic, strong
License	GNU General Public License
Filename extensions	.., .+, .a, .m[1]
Website	www.aplusdev.org
Major implementations
A+
Influenced by
APL
Influenced
K

History

In 1988, Arthur Whitney began work on the A programming language to replace APL.^[2] Other developers at Morgan Stanley extended it to A+, adding a graphical user interface (GUI) and other language features.

Arthur Whitney went on to create a proprietary array language named K. Like J, K omits the APL character set. It lacks some of the perceived complexities of A+, such as the existence of statements and two different modes of syntax.

Features

A+ provides an extended set of functions and operators, a graphical user interface with automatic synchronizing of widgets and variables, asynchronous executing of functions associated with variables and events, dynamic loading of user compiled subroutines, and other features. A+ runs on many Unix variants, including Linux. It is free and open source software released under a GNU General Public License. A newer GUI has not yet been ported to all supported platforms.

The A+ language implements the following changes to the APL language:

• an A+ function may have up to nine formal parameters
• A+ code statements are separated by semicolons, so a single statement may be divided into two or more physical lines
• The explicit result of a function or operator is the result of the last statement executed
• A+ implements an object called a dependency, which is a global variable (the dependent variable) and an associated definition that is like a function with no arguments. Values can be explicitly set and referenced in exactly the same ways as for a global variable, but they can also be set through the associated definition.

Interactive A+ development is primarily done in the Xemacs editor, through extensions to the editor. Because A+ code uses the original APL symbols, displaying A+ requires a font with those special characters; a font named kapl is provided on the web site for that purpose.