What is the definition of an open source programming language? [closed]

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Languages like Ruby and Python are usually referred-to as open source, but what makes them so?

Is it an open-source compiler?, or interpreter or execution virtual machine?

If we're talking about the compiler, then would C++ be open source?

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At the core, as others have observed, there really is no such thing as an "open source language". Only code can be open source in the strictest sense. So there can be open source compilers, runtimes, libraries, etc.

With many languages, however, the implementation (compiler/runtime) is almost inseparable from the language itself. This is the case with Ruby, Python, etc., where the language is effectively defined by its primary/original implementation. While there are other implementations of these languages, the primary implementation and the language are virtually interchangable. In such cases where the primary implementation is also open source, it makes some sense to refer to it as an open source languages, especially since such languages tend to have a community that is also almost entirely built around and friendly to open source software.

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I don't think languages are generally considered to be open source, but rather the software implementing the language (whether it's a compiler or a virtual machine or whatever). It follows that a given language can have both open-source and non-open-source implementations. For example, there are many closed-source C++ compilers, as well as open source ones.

Perhaps one could make a distinction between a language that is controlled by a single entity (eg. C#) versus a language that is grown through community contributions (eg. Python or even Java).

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I usually hear "open source language" applied to languages which are modified according to the wishes of the community. For example, Python has the PEP process, which allows anybody interested to alter the syntax / semantics of the language itself.

C and C++ are community-driven as well, though due to their age and ubiquity any changes require an incredible standardization effort. C++0x has been under design for years, and C has seen only 3 major versions (K&R, C89, C99).

Languages which are controlled by a single entity with very little community input, such as Java or C#, are usually considered "closed" regardless of the available implementations. There are GPL'd implementations of both the Java and .NET VMs available, but the language's evolution isn't community-driven. For an example of the grief this can cause, see efforts to add closures to Java.

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I must admit I've never heard of a language being referred to as open source but I guess one way of viewing it is that the two examples you have given, Ruby and Python, are (AFAIK and I'm not an expert at all in either) both non-compiled languages whereas C and C++ are compiled.

So for client-side Ruby and Python applications you have to make the code available to the user since it gets interpreted at run-time whereas for compiled languages this is optional since only the compiled executable is required.

Of course on the other hand many Ruby and Python applications will be server-side, as part of the implementation of a website for example, and so the code is interpreted on the server and therefore never visible by the end user.

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People often use the term "language" synonymously with the entire programming environment encompassing IDE, actual language, runtime environment/architecture and code libraries/frameworks. So when you say "open" I immediately think of Sun Microsystems releasing the code for the Java framework and VM as open source.

Then you have the likes of C#/.Net where the language, the core framework classes and the CLR spec are submitted to ECMA as a standard. Third parties such as Mono can implement those open, standardized components without having to license the technology and it could therefore be described as being open to an extent even though Microsoft's implementation is closed source (or only partially open anyway) and a commercial product. In Mono's case they implement some of the periphery framework classes that aren't standardised/open which is potentially a legal grey area.

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Can we consider Open source language mainly in terms of GNU licences? Or should that be only the entity [comunity, company, etc.] driven criteria?