An Implementation of J

istillcantcode

I am new to array languages, but have really enjoyed the experience of using them so far. I have consistently had much better experiences following the tutorials and doing sample problems in most of the array languages I have tried compared to other languages.

I love being able to see an example and type it my editor in without having to switch back and forth a bunch of times because I forgot some syntax by the time I switched windows. Your data is a ball of dough and you can knead it into whatever shape you want with the primitives.

Even if I don't know what the symbols are, its still easier to remember because its less stuff you have to type in. Its a little bit of work up front to learn some of the verbs (why not use Anki and some mnemonics), but you really do have so much more room to think about the problem in your head. The compression is like a cool breeze on a hot summer day.

elisbce

The more I see these languages that have neither power nor readability, the more I appreciate C.

userbinator

For those used to traditional language syntax, anything in the APL family is like Chinese to someone who only knows Latin-family natural languages. It's always amusing to see all the reaction comments when APL/J/K is posted here.

kaoD

I kinda liked J but my gripe with it is that I have to learn it almost from scratch every time I try to use it.

The tacit syntax is too idiosyncratic (I always forget the different types of verb trains) and I'm not entirely convinced it actually helped me as a "tool of thought" (but it might just be me not sticking with it long enough to be able to decode The Matrix).

I wish multidimensional arrays were a first-class citizen in my main languages though.

larodi

last updated: 2000-06-23

ofalkaed

I think this is the official J implementation as it stood in 1990 when this paper was originally published, it kept being developed but not this document which describes it. Perhaps someone else knows these details?

oddthink

The current version is at https://github.com/jsoftware/jsource

bdangubic

2.5 decades of rock solidness :)

keyle

There is a reason most modern programming languages have not followed suit on this syntax... It's pretty thick.

jandrese

> J is a dialect of APL

That is an alarming statement, especially as the first line on the site.

> Words are expressed in the standard ASCII alphabet. Primitive words are spelled with one or two letters; two letter words end with a period or a colon. The entire spelling scheme is shown in the system summary. The verb ;: facilitates exploration of the rhematic rules. Thus:

       ;: 'sum =:+/_6.95*i.3 4'
    ┌───┬──┬─┬─┬─────┬─┬──┬───┐
    │sum│=:│+│/│_6.95│*│i.│3 4│
    └───┴──┴─┴─┴─────┴─┴──┴───┘

> The source code for word formation is in the files w*.c. The process is controlled by the function wordil (word index and length) and the table state. Rows of state correspond to 10 states; columns to 9 character classes. Each table entry is a (new state, function) pair. Starting at state S, a sentence is scanned from left to right one character at a time; the table entry corresponding to the current state and character class is applied.

I'm already lost, and this is the first example.

mlochbaum

It was the subject of quite some debate, see "Panel: Is J a Dialect of APL?" at http://www.jsoftware.com/papers/Vector_8_2_BarmanCamacho.pdf . Ken and Roger backed off this stance after witnessing the controversy.

"Ken Iverson - The dictionary of J contains an introductory comment that J is a dialect of APL, so in a sense the whole debate is Ken's fault! He is flattered to think that he has actually created a new language."

null

[deleted]

ofalkaed

That example is what got me to start learning J which I have always found to be unreadable, much prefer my array languages to have their non-ascii symbols. A few nights playing with J and learning was enough to not be completely lost and able to make some progress, but it is still a challenge. When it says it "describes and implementation of J" it is not kidding, it describes the implementation and goes no further. Both the article and the code stick to this sort of terse and very concise language.

jonahx

"The reader is assumed to be familiar with J and C."

And anyone reading this at the time would have been familiar with APL as well.

It's not intended to be beginner friendly. Like J, and like the original J dictionary, the values here are brevity, compactness, and essence. There is plenty of other more beginner friendly material on J out there.

great_wubwub

Me too, but

> This document describes an implementation of J in C. The reader is assumed to be familiar with J and C.

jandrese

I have to admit I got to https://www.jsoftware.com/ioj/iojATW.htm and seriously considered if the site is just pulling my leg. I think they're being sincere but I can't be 100% sure.

jonahx

Not a joke, and a famous piece of J lore!

There have a been at least a couple attempts I've seen posted here of blog posts breaking down the code in a beginner friendly way. One I dug up is: https://blog.wilsonb.com/posts/2025-06-06-readable-code-is-u...

HN

An Implementation of J

An Implementation of J