Category:J: Difference between revisions

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== The J language ==

A frequent reaction when one first encounters a J program is often something along the lines of "that's cheating". The thought here is that the problem could not possibly be that simple, so -- instead -- the issue must be that J was specifically designed to tackle that problem.

A frequent reaction when one first encounters a J program is often something along the lines of "that's cheating". The thought here is that the problem could not possibly be that simple, so — instead — the issue must be that J was specifically designed to tackle that problem.

The flip side of this issue is that J is a dialect of APL -- a language whose development started in the 1950s and which was implemented in the early 1960s. And, originally, APL was designed as a language to describe computer architecture. The implementation as a programming language was motivated by its original successes in documenting computer hardware and instructions, and the relative simplicity of its concepts.

The flip side of this issue is that J is a dialect of APL — a language whose development started in the 1950s and which was implemented in the early 1960s. And, originally, APL was designed as a language to describe computer architecture. The implementation as a programming language was motivated by its original successes in documenting computer hardware and instructions, and the relative simplicity of its concepts.

== Introduction ==

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Object-module and imperative techniques are supported, but not required.

The J programming language was designed and developed by [~~http~~:~~//en.wikipedia.org/wiki/Kenneth_E._Iverson~~ Ken Iverson] and Roger Hui. It is a closely related successor to [[APL]], also by Iverson which itself was a successor to the notation Ken Iverson used to teach his classes about computers in the 1950s.

The J programming language was designed and developed by [[wp:Ken Iverson]] and Roger Hui. It is a closely related successor to [[APL]], also by Iverson which itself was a successor to the notation Ken Iverson used to teach his classes about computers in the 1950s.

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For example, the phrase <code>(+/ % #)</code> finds the average of a list of numbers.

~~<lang J>~~ (+/ % #) 1 2 3

(+/ % #) 1 2 3

2</lang>

2

</syntaxhighlight>

To understand how this works, you might try working with simpler sentences and their variations.

~~<lang J>~~ +/ 1 2 3

+/ 1 2 3

6

+/4 5 6

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5

(+/ % #) 4 5 6

5

5</lang>

</syntaxhighlight>

By themselves, these experiments mean nothing, but if you know that +/ was finding the sum of a list and # was finding the length of a list and that % was dividing the two quantities (and looks almost like one of the old school division symbols) then these experiments might help confirm that you have understood things properly.

== Some ~~Perspective~~ ==

== Some perspective ==

If you wish to use J you will also have to learn a few grammatical rules (J's parser has [http://www.jsoftware.com/help/dictionary/dicte.htm 9 reduction rules] and "shift" and "accept" - the above examples use four of those rules). J verbs have two definitions - a single argument "monadic" definition and a two argument "dyadic" definition.

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Discussion of the goals of the J community on RC and general guidelines for presenting J solutions takes place at [[J/HouseStyle|House Style]].

== Jedi on RosettaCode ==