K is a proprietary array processing programming language developed by Arthur Whitney and commercialized by Kx Systems. The language serves as the foundation for kdb+, an in-memory, column-based database, and other related financial products. The language, originally developed in 1993, is a variant of APL and contains elements of Scheme. Advocates of the language emphasize its speed, facility in handling arrays, and expressive syntax. History Before developing K, Arthur Whitney had worked extensively with APL, first at I. P. Sharp Associates alongside Ken Iverson and Roger Hui, and later at Morgan Stanley developing financial applications. At Morgan Stanley, Whitney helped to develop A+, a variant of APL, to facilitate migrating APL applications from IBM mainframe computers to a network of Sun workstations. A+ had a smaller set of primitive functions and was designed for speed and to handle large sets of time series data. In 1993, Whitney left Morgan Stanley and developed the first version of the K language. At the same time he formed Kx Systems to commercialize the product and signed an exclusive contract with Union Bank of Switzerland (UBS). For the next four years he developed various financial and trading applications using K for UBS. The contract ended in 1997 when UBS merged with Swiss Bank. In 1998, Kx Systems released kdb+, a database built on K. kdb was an in-memory, column-oriented database and included ksql, a query language with an SQL-like syntax. Since then, several financial products have been developed with K and kdb+. kdb+/tick and kdb+/taq were developed in 2001. kdb+, a 64-bit version of kdb+ was released in 2003 and kdb+/tick and kdb+/taq were released in 2004. kdb+ included Q, a language that merged the functions of the underlying K language and ksql. Whitney released a derivative of K called Shakti in 2018. Overview K shares key features with APL. They are both interpreted, interactive languages noted for concise and expressive syntax. They have simple rules of precedence based on right to left evaluation. The languages contain a rich set of primitive functions designed for processing arrays. These primitive functions include mathematical operations that work on arrays as whole data objects, and array operations, such as sorting or reversing the order of an array. In addition, the language contains special operators that combine with primitive functions to perform types of iteration and recursion. As a result, complex and extended transformations of a dataset can