I'm thinking about an example of a popular piece of software to illustrate the difference between Free Software and Open Source Software.

ANTLRv4 is an Open Source project and provides an online documentation sufficient to get started with the project, but mastering it requires to read the ANTLR 4 Definitive Reference. The Free Software Definition on gnu.org states that software manuals should be free.

Am I wrong if I claim that ANTLR cannot be considered as Free Software?


1 Answer 1


IMHO the existence of a book which provides detailed guidance and instruction on the use of a tool, but which costs money, does not negate the FLOSS nature of the product itself.

Though admittedly a weak analogy, gcc meets all the criteria for Free Software. But to really master C++ or C you will inevitably need to read some books on the subject, and many of those are not available for free.

I can see nothing, other than economics and the lack of comparable knowledge, to prevent someone else writing an excellent book on ANTLR which both competes with the Definitive Reference and is made available for free. This would not make the ANTLR software any more 'free'.

This approach, of providing the software for free and selling a definitive user guide, is just another approach to monetizing Open Source development. You are not forced to purchase the book in order to use the software.

You could invest $27 of your time in studying the subject matter and ANTLR source code to build the same level of expertise you can gain by purchasing the book ... but I doubt you'd get very far in a cost/benefits sense.

That said, the author does not appear to have provided any substantive FREE documentation beyond links to the book. However the e-book is non-DRM and simply googling the book's title and 'PDF' rapidly finds many places where it is available to download. I don't know the legality of those sites, and I suspect none are authorized.

  • 2
    Thanks for the insight, I think I was too nitpicky from the start. ANTLR does have a somewhat satisfying online documentation and one can easily find a very interesting talk on youtube. I believe that Prof. Parr making a living off his work is not ethically compromising. Commented Sep 23, 2015 at 8:50
  • @Awildelephant The website doesn't seem to be accessible to the general public? It requires a login and password. Actually I don' think ANTLR's documentation is satisfying at all... It all just points to sections of the book, for example in github.com/antlr/antlr4/blob/master/doc/grammars.md, which makes it extremely hard to do anything practical without the book.
    – xji
    Commented Apr 17, 2016 at 14:51
  • @XiangJi It was accessible when I wrote this comment. You can still find a lot of grammar examples here, and I personally enjoyed watching this presentation by Prof. Parr, although I don't remember if there is any concrete example in it. Otherwise you can trust StackOverflow if you have any question ;) Commented Apr 19, 2016 at 8:50

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