Say I choose to implement an interpreter or compiler for an existing programming language whose (only) reference implementation is distributed under the GPL. If in doing so I do not derive any code from this reference implementation and figure out the languages grammar/rules etc. from its official reference manual alone, does my interpreter/compiler still classify as a derivative work under the GPL? I.e. can a language "itself" fall under the GPL independent of any concrete implementation?

  • 2
    It seems to me that Crucial Question One is: did you read the code of the existing implementation at all? Or did you derive all your knowledge of the language from reading the published specifications?
    – MadHatter
    Jun 14, 2020 at 9:29
  • @MadHatter: This is so far a hypothetical scenario, but so far I have not read the implementation, only the specification and code written in that language that is not part of this implementation.
    – Peter
    Jun 14, 2020 at 9:31
  • In that case, the question simplfies to "can an API such a language description be copyrighted", which fortunately we are addressing here. Could you read that question and the answers carefully and then let us know if that addresses everything you wanted to know about the have-not-read-the-code case?
    – MadHatter
    Jun 14, 2020 at 9:37
  • I was wondering whether languages and APIs were equivalent in that sense. If that is the case then I think that link clears up my questions.
    – Peter
    Jun 14, 2020 at 9:42
  • Whether a language specification has the same copyrightability as an API is a very interesting, but much more specific, question. If I were you I'd delete this question, or accept the existing answer if it pleases you, and ask that question instead. If you want to link to this question, and the one I linked above, to show you've done your research, that will help flesh out your new question and avoid people re-treading existing ground. I'm keen to see what answers your new question gets, because I don't have a good feel for the answer myself.
    – MadHatter
    Jun 14, 2020 at 9:58

1 Answer 1


I'll answer these in reverse order because the second one is easier:

can a language "itself" fall under the GPL independent of any concrete implementation?

No. The GPL derives its legal power from copyright law, and copyright covers only the expression of an idea. The reference specification of a language can certainly be under the GPL (although the GPL is really designed for code, not documentation), but a language itself cannot be.

does my interpreter/compiler still classify as a derivative work under the GPL?

From your description, probably not, but what you're asking here is actually much more a legal question ("what does the law in jurisdiction X consider as a derivative work?") rather than an GPL question - the GPL does not (and cannot) define what a derivative work is.

  • The question of the copyrightability of ideas, and APIs in particular, is a bit more fluid and jurisdictionally-dependent than you suggest. I recommend reading this question and the answers thereto before being quite so sure about the statement.
    – MadHatter
    Jun 14, 2020 at 9:35

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