Re: Parsing Expression Grammar

Laurence Finston <>
2 Sep 2005 14:19:31 -0400

          From comp.compilers

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Parsing Expression Grammar (2005-08-31)
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From: Laurence Finston <>
Newsgroups: comp.compilers
Date: 2 Sep 2005 14:19:31 -0400
Organization: GWDG, Goettingen
References: 05-08-115
Keywords: parse, administrivia
Posted-Date: 02 Sep 2005 14:19:31 EDT

On Wed, 31 Aug 2005 wrote:

> I know the Rats! package generates parsers based on
> PEG, but since Rats! is GPL`d I can`t use it for commercial use.

No, the GNU General Public License does allow commercial use, under
specified conditions. If you modify software licensed under the GNU
GPL, you may not be able to use it in the way you want, but you can
certainly charge money for it.

This is an excerpt from the FAQ for the GPL at

      If I use a piece of software that has been obtained under
      the GNU GPL, am I allowed to modify the original code into a
      new program, then distribute and sell that new program

      You are allowed to sell copies of the
      modified program commercially, but only under the terms of
      the GNU GPL. Thus, for instance, you must make the source
      code available to the users of the program as described in
      the GPL, and they must be allowed to redistribute and modify
      it as described in the GPL.

      These requirements are the condition for including the
      GPL-covered code you received in a program of your own.

This refers to modifying GPL'd software. Merely using it in
combination with your own software is an entirely different matter,
and in most cases should not cause problems.

Problems can arise when a GPL'd program produces output files, and
these output files contain a license. GNU packages do not usually do
this. Clearly, it is possible to use GCC to compile commercial
software, GNU Emacs to write files used for commercial purposes,
etc. It is certainly not my intention that all drawings made with GNU
3DLDF should be free in the sense of the GNU GPL. My own are not,
unless I decide to make them so.

> It would help to actually see the set of needed production rules for
> the Java language as a base for designing a new language.

I don't see any reason why you can't study Free Software. That's what
it's there for (among other things). However, if you use any of the
code, then you must respect the terms of the license, or you will be
violating the rights of the copyright holder.

Of course, studying software and then writing one's own implementation
is a tricky issue. Both the _Numerical Recipes_ books and _The NURBs
Book_ contain non-free code which can be studied but not used, unless
one obtains a license from the copyright holders. I've been very
hesitant to read such code. How is it possible not to be influenced
by it, when you go to write your own? What if you see a great
programming idiom that never would have occurred to you?

Laurence Finston

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