如何使用XText创建方言

Question

The project I'm working on has a custom file format, with a pre-defined structure. The structure is really simple and generic (and I cannot change it): it is composed by (nested) commands and typed properties.

Using this structure, several dialects have been created. The dialects are an "instantiation" of the generic grammar, and specify the name and the meaning of commands and the expected properties.

I created a model with EMF for one of these dialects, and I would like to reuse XText to easily create a professional text editor and be able to read and write my model into the correct format.

Now I have a choice. On one side, I can directly target the dialect, and mix in the same grammar the concepts from the custom file structure and those from the dialect. On the other side, I can create a grammar describing the file structure, and on top of this I can describe my dialect.

Which way I should follow? I think that the latter is the best one, but how can I create a grammar describing those two layers?

Answer 1

Xtext allows extending existing languages: in the head of the grammar you could specify a parent grammar, that gets inherited.

For an example, see the Domain model example from Xtext 2.0, that extends the XBase language:

grammar org.eclipse.xtext.example.domainmodel.Domainmodel with org.eclipse.xtext.xbase.Xbase

Every grammar element can be replaced by new syntax; new validation can be added, etc. See the following blog posts for further ideas: http://koehnlein.blogspot.com/2011/07/extending-xbase.html

You can use the same approach: create a base language, then extend them for your various dialects.