K (programming language)
Encyclopedia
K is a proprietary array processing 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 its expressive syntax.
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 the migration of APL applications from IBM
mainframes
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 a SQL
-like syntax. Since then, a number of 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 brought out in 2003 and kdb+/tick and kdb+/taq were brought out the following year. kdb+ included Q
, a language that merged the functionality of the underlying K language and ksql.
Like APL, the primitive functions and operators are represented by single or double characters; however, unlike APL, K restricts itself to the ASCII character set (a feature it shares with J
, another variant of APL). To allow for this, the set of primitive functions for K is smaller and heavily overloaded, with each of the ASCII symbols representing two or more distinct functions or operations. In a given expression, the actual function referenced is determined by the context. As a result K expressions can be opaque and difficult to parse. For example, in the following contrived expression the exclamation point “!” refers to three distinct functions:
Reading from right to left the first ! is modulo division that is performed on 7 and 4 resulting in 3. The next ! is enumeration and lists the integers less than 3, resulting in the list 0 1 2. The final ! is rotation where the list on the right is rotated two times to the left producing the final result of 2 0 1.
The second core distinction of K is that functions are first-class objects, a concept borrowed from Scheme. First-class function
s can be used in the same contexts where a data value can be used. Functions can be specified as anonymous expressions and used directly with other expressions. Function expressions are specified in K using curly brackets. For example, in the following expression a quadratic expression is defined as a function and applied to the values 0 1 2 and 3:
In K, named functions are simply function expressions stored to a variable in the same way any data value is stored to a variable.
Functions can be passed as an argument to another function or returned as a result from a function.
The following expression sorts a list of strings by their lengths:
The expression is evaluated from right to left as follows:
A function to determine if a number is prime can be written as:
The function is evaluated from right to left:
If x is not prime then one of the values returned by the modulo operation will be 0 and consequently the minimal value of the list. If x is prime then the minimal value will be 1, because x mod 2 is 1 for any prime greater than 2.
The function below can be used to list all of the prime numbers between 1 and R with:
The expression is evaluated from right to left
library included in K is based on that of A+, but it takes advantage of many features unique to K. K's GUI is declarative and data-driven, as opposed to most GUIs which are imperative. A window and the things in a window are contained in a normal data structure, usually a dictionary on the K Tree, and displayed with the $ operator. Information about a widget
is kept in the variable's attributes. Every data type in K can function as a widget - just not necessarily very well.
But in K, the GUI library is so terse and easy to use that even for prototyping, developers often use a GUI interface rather than a command line. A minimal, not very pretty GUI Hello world in K is
`show$"Hello world"
The latest version of the K programming language, known as "K4", no longer has a built-in GUI library.
. The database supports SQL
, (SQL-92
) and ksql, a query language with a syntax similar to SQL and designed for column based queries and array analysis.
kdb is available for Solaris, Linux
, and Windows
(32-bit or 64-bit).
Database
A database is an organized collection of data for one or more purposes, usually in digital form. The data are typically organized to model relevant aspects of reality , in a way that supports processes requiring this information...
, 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 its expressive syntax.
History
Before developing K, Arthur Whitney had worked extensively with APL, first at I. P. Sharp AssociatesI. P. Sharp Associates
I. P. Sharp Associates, IPSA for short, was a major Canadian computer time sharing, consulting and services firm of the 1970s and 80s. IPSA is particularly well known for its work on the APL programming language, an early packet switching computer network known as IPSANET, and a powerful...
alongside Ken Iverson
Kenneth E. Iverson
Kenneth Eugene Iverson was a Canadian computer scientist noted for the development of the APL programming language in 1962. He was honored with the Turing Award in 1979 for his contributions to mathematical notation and programming language theory...
and Roger Hui
Roger Hui
Roger Hui is a computer scientist and co-developer of the J Programming Language.He was born in Hong Kong and he immigrated to Canada with his entire family in 1966.-Education and career:In 1973, Hui entered the University of Alberta...
, and later at Morgan Stanley
Morgan Stanley
Morgan Stanley is a global financial services firm headquartered in New York City serving a diversified group of corporations, governments, financial institutions, and individuals. Morgan Stanley also operates in 36 countries around the world, with over 600 offices and a workforce of over 60,000....
developing financial applications. At Morgan Stanley, Whitney helped to develop A+
A+ (programming language)
A+ is an array programming language descendent from the programming language A, which in turn was created to replace APL in 1988. Arthur Whitney developed the "A" portion of A+, while other developers at Morgan Stanley extended it, adding a graphical user interface and other language features...
, a variant of APL, to facilitate the migration of APL applications from IBM
IBM
International Business Machines Corporation or IBM is an American multinational technology and consulting corporation headquartered in Armonk, New York, United States. IBM manufactures and sells computer hardware and software, and it offers infrastructure, hosting and consulting services in areas...
mainframes
Mainframe computer
Mainframes are powerful computers used primarily by corporate and governmental organizations for critical applications, bulk data processing such as census, industry and consumer statistics, enterprise resource planning, and financial transaction processing.The term originally referred to the...
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
Union Bank of Switzerland
Union Bank of Switzerland was a large integrated financial services company located in Switzerland. The bank, which at the time was the second largest bank in Switzerland, merged with Swiss Bank Corporation in 1998, to become UBS to form what was then the largest bank in Europe and the second...
(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
Swiss Bank Corporation
Swiss Bank Corporation was a large integrated financial services company located in Switzerland...
. In 1998, Kx Systems released kdb, a database built on K. kdb was an in-memory, column-oriented
Column-oriented DBMS
A column-oriented DBMS is a database management system that stores its content by column rather than by row. This has advantages for data warehouses and library catalogues where aggregates are computed over large numbers of similar data items....
database and included ksql, a query language with a SQL
SQL
SQL is a programming language designed for managing data in relational database management systems ....
-like syntax. Since then, a number of 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 brought out in 2003 and kdb+/tick and kdb+/taq were brought out the following year. kdb+ included Q
Q (programming language from Kx Systems)
Q is a proprietary array processing language developed by Arthur Whitney and commercialized by Kx Systems. The language serves as the query language for kdb+, a disk based and in-memory, column-based database. kdb+ is based upon K, a terse variant of APL...
, a language that merged the functionality of the underlying K language and ksql.
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 be expressed as a chain of sub-expressions, with each link performing a segment of the calculation and passing the results to the next link in the chain.Like APL, the primitive functions and operators are represented by single or double characters; however, unlike APL, K restricts itself to the ASCII character set (a feature it shares with J
J (programming language)
The J programming language, developed in the early 1990s by Kenneth E. Iverson and Roger Hui, is a synthesis of APL and the FP and FL function-level languages created by John Backus....
, another variant of APL). To allow for this, the set of primitive functions for K is smaller and heavily overloaded, with each of the ASCII symbols representing two or more distinct functions or operations. In a given expression, the actual function referenced is determined by the context. As a result K expressions can be opaque and difficult to parse. For example, in the following contrived expression the exclamation point “!” refers to three distinct functions:
2!!7!4
Reading from right to left the first ! is modulo division that is performed on 7 and 4 resulting in 3. The next ! is enumeration and lists the integers less than 3, resulting in the list 0 1 2. The final ! is rotation where the list on the right is rotated two times to the left producing the final result of 2 0 1.
The second core distinction of K is that functions are first-class objects, a concept borrowed from Scheme. First-class function
First-class function
In computer science, a programming language is said to have first-class functions if it treats functions as first-class objects. Specifically, this means that the language supports passing functions as arguments to other functions, returning them as the values from other functions, and assigning...
s can be used in the same contexts where a data value can be used. Functions can be specified as anonymous expressions and used directly with other expressions. Function expressions are specified in K using curly brackets. For example, in the following expression a quadratic expression is defined as a function and applied to the values 0 1 2 and 3:
{(3*x^2)+(2*x)+1}'!4In K, named functions are simply function expressions stored to a variable in the same way any data value is stored to a variable.
x:25
f:{(x^2)-1}
Functions can be passed as an argument to another function or returned as a result from a function.
Examples
K is an interpreted language where every statement is evaluated and its results immediately displayed. Literal expressions such as strings evaluate to themselves. Consequently, the Hello world-program is trivial:
"Hello world!"
The following expression sorts a list of strings by their lengths:
x@>#:'x
The expression is evaluated from right to left as follows:
- #:'x returns the length of each word in the list x.
- > returns the indices that would sort a list of values in descending order.
- @ use the integer values on the right to index into the original list of strings.
A function to determine if a number is prime can be written as:
{&/x!/:2_!x}
The function is evaluated from right to left:
- !x enumerate the positive integers less than x.
- 2_ drops the first two elements of the enumeration (0 and 1).
- x!/: performs modulo division between the original integer and each value in the truncated list.
- &/ find the minimum value of the list of modulo result.
If x is not prime then one of the values returned by the modulo operation will be 0 and consequently the minimal value of the list. If x is prime then the minimal value will be 1, because x mod 2 is 1 for any prime greater than 2.
The function below can be used to list all of the prime numbers between 1 and R with:
(!R)@&{&/x!/:2_!x}'!R
The expression is evaluated from right to left
- !R enumerate the integers less than R.
- ' apply each value of the enumeration to the prime number function on the left. This will return a list of 0's and 1's.
- & return the indices of the list where the value is 1.
- @ use the integer values listed on the right to index into the list on the left.
- (!R) A list of integers less than R.
Performance characteristics
The performance of modern CPUs is improving at a much faster rate than their memory subsystems. The small size of the interpreter and compact syntax of the language makes it possible for K applications to fit entirely within the level 1 cache of the processor. Vector processing makes efficient use of the cache row fetching mechanism and posted writes without introducing bubbles into the pipeline by creating a dependency between consecutive instructions.GUI
The GUIGraphical user interface
In computing, a graphical user interface is a type of user interface that allows users to interact with electronic devices with images rather than text commands. GUIs can be used in computers, hand-held devices such as MP3 players, portable media players or gaming devices, household appliances and...
library included in K is based on that of A+, but it takes advantage of many features unique to K. K's GUI is declarative and data-driven, as opposed to most GUIs which are imperative. A window and the things in a window are contained in a normal data structure, usually a dictionary on the K Tree, and displayed with the $ operator. Information about a widget
Widget (computing)
In computer programming, a widget is an element of a graphical user interface that displays an information arrangement changeable by the user, such as a window or a text box. The defining characteristic of a widget is to provide a single interaction point for the direct manipulation of a given...
is kept in the variable's attributes. Every data type in K can function as a widget - just not necessarily very well.
But in K, the GUI library is so terse and easy to use that even for prototyping, developers often use a GUI interface rather than a command line. A minimal, not very pretty GUI Hello world in K is
`show$"Hello world"
The latest version of the K programming language, known as "K4", no longer has a built-in GUI library.
K financial products
K is the foundation for a family of financial products. Kdb is an in-memory, column-based database with much of the same functionality of a relational database management systemRelational database management system
A relational database management system is a database management system that is based on the relational model as introduced by E. F. Codd. Most popular databases currently in use are based on the relational database model....
. The database supports SQL
SQL
SQL is a programming language designed for managing data in relational database management systems ....
, (SQL-92
SQL-92
SQL-92 was the third revision of the SQL database query language. Unlike SQL-89, it was a major revision of the standard. For all but a few minor incompatibilities, the SQL-89 standard is forwards-compatible with SQL-92....
) and ksql, a query language with a syntax similar to SQL and designed for column based queries and array analysis.
kdb is available for Solaris, Linux
Linux
Linux is a Unix-like computer operating system assembled under the model of free and open source software development and distribution. The defining component of any Linux system is the Linux kernel, an operating system kernel first released October 5, 1991 by Linus Torvalds...
, and Windows
Microsoft Windows
Microsoft Windows is a series of operating systems produced by Microsoft.Microsoft introduced an operating environment named Windows on November 20, 1985 as an add-on to MS-DOS in response to the growing interest in graphical user interfaces . Microsoft Windows came to dominate the world's personal...
(32-bit or 64-bit).
See also
- APL, the first array language
- JJ (programming language)The J programming language, developed in the early 1990s by Kenneth E. Iverson and Roger Hui, is a synthesis of APL and the FP and FL function-level languages created by John Backus....
, another APL-inspired language - QQ (programming language from Kx Systems)Q is a proprietary array processing language developed by Arthur Whitney and commercialized by Kx Systems. The language serves as the query language for kdb+, a disk based and in-memory, column-based database. kdb+ is based upon K, a terse variant of APL...
, the language of kdb+ and a new merged version of K and ksql.
External links
- Kx Systems
- Official page for KDB+
- Overview of K
- A Shallow Introduction to the K programming language Article from Kuro5hinKuro5hinKuro5hin is a collaborative discussion website. Articles are created and submitted by Kuro5hin's users and submitted to queue for evaluation. Site members can vote for or against publishing an article and, once the article has reached a certain number of votes, it is then published to the site...
- Dennis Shasha - K as a Prototyping Language
- Michael Schidlowsky - Screencast comparing solutions of a specific problem in K vs. JavaJava (programming language)Java is a programming language originally developed by James Gosling at Sun Microsystems and released in 1995 as a core component of Sun Microsystems' Java platform. The language derives much of its syntax from C and C++ but has a simpler object model and fewer low-level facilities...
- code.kx.com username:anonymous, password:anonymous
- First Derivatives
- Skelton Consulting GmbH
- Symagon GmbH