APL is an acronym for "A Programming Language." APL is used over a wide range of applications, varying from testing of prototypes, to administrative activities, to diverse scientific tasks. Kenneth Iverson designed the general-purpose language in the 1960s. Iverson's original intent in developing APL was not to create a programming language, but rather to create a mathematical means of describing how computers are assembled and operate. As the APL initiative grew, Iverson was joined by Adin Falkoff, Larry Breed and Philip Abrahams, who took on the task of using their mathematical notation as a programming language. Whereas many computer languages began as tools for specifying machine instructions in a system-dependent manner that attempts to mesh the language with the technology, APL's mathematical derivation was unfettered by computer hardware.
The group's efforts culminated in the release of the APL computer programming language in 1966. Thus, APL is an old computer language, similar in vintage as ALGOL (1958), Basic (1965), COBOL (1960), FORTRAN (1953) and PL/I (1965). Nonetheless, many ideas in APL are still considered unique, and other features have been incorporated into other programming languages.
APL is one of the two early dynamic languages, along with SNOBOL. These languages were at first considered more as curiosities than valuable. With time, however, the value of their dynamic characters was recognized. In dynamic languages, actions are programmed to occur as they are needed, rather than before they are needed. This involves the dynamic allocation of memory.
Some of the individuals who were involved in the creation of APL subsequently created STS (Scientific Time-Sharing Corporation, now called Manugistics, Inc.) in the 1970s. STSC created a business applications version of APL (APL PLUS) that remains a strong system. The latest version of APL is APL+Win 3.6
APL was at first utilized mainly on large, mainframe computers. Microcomputers did not possess the storage capacity or speed to handle the language. Advancement in microcomputer technology, however, now allows APL to run comfortably on nearly all computers.
APL is an interactive programming language, meaning that the system displays a prompt and then waits for the user to give the prompt what is termed an APL expression. It was best known for its use of non-ASCII symbols, including Greek letters, although some aspects of ASCII have been incorporated into later versions of APL. Operations such as sorting, searching and selection are built into the language. These built-in features make APL shorter, and easier to write, repair, and modify than other programming languages. Once an expression has been given, the APL system computes, or evaluates, the expression and prints its value. The cycle continues until the user terminates the session. As an example, the following could be an APL session:
<tab4 + 5
9
<tab2 + 4+ 6
12
<tab )OFF
As is illustrated above, APL is intuitive in the sense that the mathematical symbols for addition, subtraction and multiplication convey their traditional mathematical function. In APL, expressions are always read in a right-associative manner. As examples, 2 x 3 + 4 is read and mathematically interpreted as 2 x (3 + 4), and 1-2-3-4 is read as 1-(2-(3-4)). There are a number of other symbols in APL, which are unique to the language, to assign functions including raising a number to a power, natural logarithm and absolute value.
One aspect of APL that has ensured its popularity is that it is a development language that permits very fast program development. Such speed is vital in a commercial environment, where time spent developing a program is time that is not generating revenue. Also, scientists benefit from a language that permits the rapid modification of the analysis software to changing research interests. Another beneficial aspect of APL is that one well-versed programmer is sufficient to maintain the program and handle complex computing problems; a team of programmers is not necessary.
Another language developed by Ken Iverson called J is similar to APL. J is actually a derivation of APL, one that uses the ASCII character set. Like APL, J is an array language, that is, the objects (integers or characters, anything that has a defined data type) grouped together are of the same data type, and the entire array is stored in memory. An array language such as APL or J is suited towards tasks involving calculations with more than one number at any one time, or more than one name in a list.
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