SafekipediaAPL (programming language)
Adapted from Wikipedia · Adventurer experience
APL is a special kind of programming language made in the 1960s by Kenneth E. Iverson. It works mostly with something called multidimensional arrays, which are like neat tables of numbers and data.
What makes APL different is that it uses many special symbols instead of normal letters for its functions and operations. This lets people write very short and strong programs.
Because of its smart ways of handling data, APL has helped many areas, like spreadsheets, functional programming, and tools for doing math on computers. It has also inspired the making of several other programming languages.
History
Mathematical notation
A way to write math for working with groups of numbers, called arrays, was created by Kenneth E. Iverson while he was at Harvard University. He kept working on it in 1960 while he was at IBM, together with Adin Falkoff. He wrote a book about it in 1962 called A Programming Language. This special way of writing math was used inside IBM for small reports about computers.
Iverson also used his special math writing in a draft chapter for a book he was writing with Fred Brooks, called Automatic Data Processing. That book came out in 1963. In 1979, Iverson got a big award called the Turing Award for his work on this math writing system.
Development into a computer programming language
In 1962, some people tried to use this math writing to describe a whole computer system. In 1963, a person named Herbert Hellerman put part of this writing into an IBM 1620 computer. Students used it in a special class about calculating functions. This early version was called Personalized Array Translator, or PAT.
Later, Iverson and others at IBM used the writing to describe how the IBM System/360 computers worked. After that, they wanted to make it work on a real computer. A person named John Lawrence asked them to help use this writing to teach people how to use computers.
Some people joined the team and they made a version of the writing work on an IBM 7090 computer. They finished this in late 1965 and called it IVSYS. They used special English words instead of the normal symbols because the computer could not show the special symbols.
Hardware
Before computers had screens, a special typewriter was made that had all the special symbols needed for this writing. This helped programmers type and see the symbols correctly. Later, a screen made by Tektronix could show these symbols too.
Commercial availability
The first time someone could use this writing interactively on a computer was in 1966. IBM started sharing a free version of this writing for the IBM 1130 computer in 1968. It could run with very little memory.
This writing became popular on big computers from the late 1960s to the early 1980s because it could support many users even on simpler machines. IBM made improvements to make it run faster on some of their big computers.
In the 1970s and 1980s, this writing was used on many different kinds of computers from many companies. Companies like IP Sharp Associates and Scientific Time Sharing Corporation offered services where people could use this writing on shared computers. By the mid-1980s, as cheaper personal computers became available, most people stopped using these shared services.
Microcomputers
When small computers became popular in the mid-1970s, a language called BASIC was more common. But some small computers still used this special writing. For example, the MCM/70 from 1974 and the VideoBrain Family Computer from 1977 came with their own versions of this writing. The Commodore SuperPET from 1981 also had a version made by the University of Waterloo.
APL2
In the early 1980s, IBM made a new version of this writing called APL2. This version allowed arrays to contain other arrays, which made programming easier. APL2 became the standard for new versions of this writing on different computers. Today, many companies say they are compatible with APL2 to show their products work well.
Modern implementations
New versions of this writing made by companies like APLX and Dyalog add features like object-oriented programming and support for modern technologies. There are also free versions like GNU APL for Linux and NARS2000 for Windows.
Derivative languages
This special writing influenced many other programming languages, such as A and A+, FP, Ivy, J, K, MATLAB, Nial, S, Snap_!_, Speakeasy, and the Wolfram Language.
Language characteristics
Main articles: APL (codepage) and syntax and symbols
APL is known for its special set of characters. In the past, it was hard to show these characters on old screens or printers, but today this is easier.
Unlike many other programming languages, APL uses chains of functions and operators that work on arrays of data. It can do complex tasks in just one line of code, making it very powerful for certain problems. The language has its own special symbols, which can seem unusual at first but become familiar with use.
n ← 4 5 6 7
| Assigns vector of values, {4 5 6 7}, to variable n, an array create operation. An equivalent yet more concise APL expression would be n ← 3 + ⍳4. Multiple values are stored in array n, the operation performed without formal loops or control flow language. |
n
4 5 6 7
| Display the contents of n, currently an array or vector. |
n+4
8 9 10 11
| 4 is now added to all elements of vector n, creating a 4-element vector {8 9 10 11}. As above, APL's interpreter displays the result because the expression's value was not assigned to a variable (with a ←). |
+/n
22
| APL displays the sum of components of the vector n, i.e., 22 (= 4 + 5 + 6 + 7) using a very compact notation: read +/ as "plus, over..." and a slight change would be "multiply, over..." |
m ← +/3+⍳4
m
22
| These operations can be combined into one statement, remembering that APL evaluates expressions right to left: first ⍳4 creates an array, [1,2,3,4], then 3 is added to each component, which are summed together and the result stored in variable m, finally displayed. In normal mathematical notation, it is equivalent to: m = ∑ i = 1 4 ( i + 3 ) {\displaystyle \displaystyle m=\sum \limits _{i=1}^{4}(i+3)} . Recall that mathematical expressions are not read or evaluated from right-to-left. |
| Term | Description |
|---|---|
| function | operation or mapping that takes zero, one (right) or two (left & right) arguments which may be scalars, arrays, or more complicated structures, and may return a similarly complex result. A function may be: Primitive: built-in and represented by a single glyph; Defined: as a named and ordered collection of program statements; Derived: as a combination of an operator with its arguments. |
| array | data valued object of zero or more orthogonal dimensions in row-major order in which each item is a primitive scalar datum or another array. |
| niladic | not taking or requiring any arguments, nullary |
| monadic | requiring only one argument; on the right for a function, on the left for an operator, unary |
| dyadic | requiring both a left and a right argument, binary |
| ambivalent or monadic | capable of use in a monadic or dyadic context, permitting its left argument to be elided |
| operator | operation or mapping that takes one (left) or two (left & right) function or array valued arguments (operands) and derives a function. An operator may be: Primitive: built-in and represented by a single glyph; Defined: as a named and ordered collection of program statements. |
Naming
APL is named after Iverson's book called A Programming Language. The book talks about Iverson's ideas, not the language itself. The name was first used when making APL\360.
Adin Falkoff came up with the name in 1966 while working on APL\360 at IBM. He wrote "A Programming Language" on a board and wrote "APL" below it. That’s how APL got its name. Later, some people began calling it "Array Programming Language" or "Array Processing Language," which turned APL into a backronym.
Logo
People who used APL often met for conferences from 1969 to 2010. At these meetings, they sometimes gave out items like stickers or cards with APL designs or pictures of apples (because "apple" sounds like "APL"). They also used special symbols from the APL keyboard.
Because APL didn’t have one main logo that everyone used, a group called the British APL Association started a project in 2021 to create one. After many people voted and gave feedback, they finally chose a logo in May 2022.
Use
APL is used for many jobs, like handling money and insurance. It is also used to make smart machines and control robots. Some people think APL is good for calculations because of its special symbols. This makes it popular with experts who study data.
APL is good at changing pictures and making animations. A company called Digital Effects used APL to help make TV ads and the 1982 movie Tron. Today, APL is still used for important jobs, like managing investments, health information, and studying DNA.
Notable implementations
APL\360
The first version of APL to use its special symbols was APL\360, running on the IBM System/360. It was finished in 1966 but was only used inside IBM at first. In 1973, its creators won an award for making APL\360 simple and fast.
In 1975, the IBM 5100 microcomputer included APL\360 as one of its built-in languages, with a special keyboard and screen for its symbols.
APL\1130
In 1968, APL\1130 became the first APL system that anyone could use. It was made by IBM for the IBM 1130 and became very popular.
APL*Plus and Sharp APL
Main articles: I. P. Sharp Associates and Scientific Time Sharing Corporation
APL*Plus and Sharp APL are versions of APL\360 with extra features for business use. They were made by two companies using some of the original APL\360 team members.
APL2
APL2 was a new version of APL made by IBM from 1971 to 1984. It added support for more complex data arrangements.
APLGOL
In 1972, APLGOL was an experimental version of APL that added new ways to organize commands.
Dyalog APL
Dyalog APL was first released in 1983 by a British company and works on many computers today. It is based on APL2 and adds more programming styles.
NARS2000
NARS2000 is a free APL version made by Bob Smith. It runs on Microsoft Windows and other systems.
APLX
APLX is a version of APL that works on many platforms. It was made by a British company in 2002 but is now free.
York APL
York APL was made at York University around 1968. It worked on IBM 360 computers and had a small difference in how it handled single values.
GNU APL
GNU APL is a free version of APL that works on many operating systems. It was written by Jürgen Sauermann.
Interpretation and compilation of APL
APL is usually an interpreted language, meaning it runs directly without being changed into machine code first. It has some features, like weak variable typing, that make it hard to turn into fast-running code through compilation. But because APL works with arrays, it can do some tasks very quickly by using parallelism, parallel computing, massively parallel methods, and very-large-scale integration (VLSI).
APL is not always just interpreted. There are ways to make it faster, like idiom recognition, where common patterns are treated as single steps. Another method is creating optimised bytecode, which simplifies some steps the computer needs to do. Some versions of APL, like Dyalog APL, use this method. Researchers have also tried to compile APL into machine code since the 1970s. Tools like the STSC APL Compiler mix bytecode optimization with compilation, turning some parts of APL into fast machine code when possible.
Standards
APL became an official standard by groups like the American National Standards Institute (ANSI), the International Organization for Standardization (ISO), and the International Electrotechnical Commission (IEC). There are two main standards: one for basic APL from 1989, and another for an expanded version from 2001.
Related articles
This article is a child-friendly adaptation of the Wikipedia article on APL (programming language), available under CC BY-SA 4.0.
Images from Wikimedia Commons. Tap any image to view credits and license.