The J Programming LanguageΒΆ
| Authors: | Tracy Harms @kaleidic |
|---|---|
| Time: | 15:50 - 16:20 |
| Session: | https://thestrangeloop.com/sessions/the-j-programming-language |
| Link: | http://www.jsoftware.com/ |
| Slides: |
Tracy didn’t create J, but he’s here to talk about it. J is the product of Kenneth E. Iverson adn Roger Hui. J was first released in 1990.
What sort of problem does J fit well? Subtraction. Specifically image subtraction: removing a shadow from an image.
[Shows the source, fits on one slide.]
When reading a J program, it’s often best to start at the end: that’s the punch line. And then start back at the top to see how it gets there.
[Walks through image subtraction program.]
J favors an interactive approach, assuming the “operator” is at the console.
In J, data is called a noun, and a noun is a collection. Nouns are regular. Scalar data is the exception, rather than the rule. A verb (function) applies across
J has had over fifty years of refinement, starting on chalkboards in 1957 with Iverson at Harvard. In 1962, there was a book published on it: “A Programming Language”. A paper followed in 1964, desribing the System/360 architecture. The interpreter, APL, was released in 1966: before then verification and changes happened manually, with pencil and paper.
Even though APL was critically important, Iverson had a sense that it could have been better had he known more starting out. In the 1980’s he released its successor, J.
[Shows some J interaction.]
In J you can factor verbs that take common nouns out into a verb train. If you give that train a name, you’ve defined a new verb.
average =: +/ % #
allows you to do:
average MyList
And is equivalent to:
(+/MyList) % (#MyList)
(The sum of the list divided by the number of elements.)
Verb Trains are higher order functions, denoted by placing verbs adjacent to one another.
[Shows numeronym example.]