The language looks interesting, but I am a bit concerned about the license situation, as in my understanding they have misinterpreted the GPL with regard to shared libraries. Quoting:
Various libraries used by the Julia environment include their own licenses such as the GPL, LGPL, and BSD (therefore the environment, which consists of the language, user interfaces, and libraries, is under the GPL). Core functionality is included in a shared library, so users can easily and legally combine Julia with their own C/Fortran code or proprietary third-party libraries.
If the program dynamically links plug-ins, and they make function calls to each other and share data structures, we believe they form a single program, which must be treated as an extension of both the main program and the plug-ins. In order to use the GPL-covered plug-ins, the main program must be released under the GPL or a GPL-compatible free software license, and that the terms of the GPL must be followed when the main program is distributed for use with these plug-ins.
I believe what they're saying is that there are two things:
1. The Julia core, which consists of the language runtime and core functionality, is MIT licensed, and builds into an MIT-licensed shared library.
2. The Julia "environment", which includes a user interface, third-party libraries, etc., some of which are GPL, and which is therefore GPL as a whole.
I believe they're saying that you can link #1 with proprietary code, not meaning to imply that you can link #2 with proprietary code (because as you point out that wouldn't work). How useful that is probably depends on how many of the libraries the average application needs are in bucket #1.
That is exactly right. At the moment I think the only GPL library Julia uses is readline — but obviously that's pretty important for the repl, so we chose to do it this way.
The last REPL I wrote used linenoise ( https://github.com/antirez/linenoise ) instead of readline, and it worked great for us. You may need more of readline's features than we did, but it's worth a look.
The FSF interpretation is undermined by the existence of non-GPL Linux programs (that link, call and use data structures from the (GPL-licensed) Linux API).
Various libraries used by the Julia environment include their own licenses such as the GPL, LGPL, and BSD (therefore the environment, which consists of the language, user interfaces, and libraries, is under the GPL). Core functionality is included in a shared library, so users can easily and legally combine Julia with their own C/Fortran code or proprietary third-party libraries.
The FSF disagrees (http://www.gnu.org/licenses/gpl-faq.html#NFUseGPLPlugins):
If the program dynamically links plug-ins, and they make function calls to each other and share data structures, we believe they form a single program, which must be treated as an extension of both the main program and the plug-ins. In order to use the GPL-covered plug-ins, the main program must be released under the GPL or a GPL-compatible free software license, and that the terms of the GPL must be followed when the main program is distributed for use with these plug-ins.