Guides/General FAQ/J License

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What should I know about J licenses?

Please note this Wiki page is user-written; for J Software's official policy on source, see .

  • Is J open source?
  • Where is the source code for J?
  • Is J under the GPL?
  • What license is J's source under?

The J interpreter is not open source. J Software, which owns and develops the J language, is a commercial venture. Part of J Software's revenue stream is selling its source code. Often, this is to companies with a large codebase or other stake in J, and owning the source provides them the confidence that they may continue their J-based business, should J Software (or their relationship with J Software) disappear.

That said: while the J interpreter is not open source, the Dictionary of J is readable by anyone. The Dictionary is the abstract, Platonically ideal, J. Any interpreter which implements its specification is as valid a "J" as the one provided by J Software (hence the title of the paper "__An__ Implementation of J"). What remains is for an open source initiative to turn the English of the Dictionary into compilable code.

While no such intiative yet exists, Oleg Kobchenko and Andrew Nikitin have started an effort at Further, prior to 1995, J's source was available. As of this writing in 2006, you can still find the source code to early versions of J in old FTP archives. While the language has changed significantly since then, the source might still be useful as seed code, or at least instructive in style.