Saturday, August 6, 2011

Project Schliemann/ GLF/ Generic Language Framework with Netbeans

I've been trying for some time to get editing support in Netbeans for my custom language. There are many different APIs for doing this, depending on the version of Netbeans and the level of integration you want. Unfortunately, for my purposes there was only one API which was not ridiculously over-complex, called Project Schliemann (or alternately ".nbs files", or the "Generic Languages Framework"). The basic idea is that you write a single file with the grammar and rules about your language, and a generic parser reads that file and then can do some basic syntax checking, etc. on your code. Unfortunately, with recent versions of Netbeans, it has been removed. In addition, with version 6.0, I encountered a bug which prevented me from using it. This bug is fixed in 6.1, which is the version I ended up using.

After many tutorials and searching online, as well as several attempts for me to write or copy an NBS file, I still had made no progress. As a last ditch effort, I decided to try to find a complete working GLF Netbeans Project, to see if perhaps the entire API was broken. I discovered a Prolog Language support module, written by Rosa Gutierrez, on this page: unfortunately, the link to the source was dead! So I emailed her, and she was able to send me a copy of the source, which you can now download here.

Once I had a working module, I was able to incrementally modify it to do what I wanted. However, there is one catch which I didn't notice anywhere else: Even if your grammar would accept the contents of a file, if there is something in your file which is not defined as one of the tokens, then it will give you an error, even if that exact token is listed in your grammar as acceptable. That's a little confusing, but the basic idea is that even if your grammar defines

Statement = "Hello" | "Goodbye";

if "hello" and "goodbye" do not somehow fall under the category of one of the tokens you defined, you will get an error.

Also, another quirk of the grammar is that the "root" of the grammar must be labeled "S". So for example, a simple grammar might be entirely defined like

S = "hello world" | "goodbye world";

I'll post any more quirks or tips I encounter here.

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