The following instructions show how to go about starting a new back-end for a new language "XYZ" using the Java back-end as a basis.
All the files in the antlr-3.0/runtime/Java/src/org/antlr/runtime directory are needed to create
a full back-end. You must also copy another group of templates such as antlr-3.0/src/org/antlr/codegen/templates/Java/*.stg. And create antlr-3.0/src/org/antlr/codegen/XYZTarget.java if you need to override anything in Target.java.
But it is in fact pretty easy to get started:
- In src/org/antlr/codegen/templates/
- create a directory XYZ
- copy Java/Java.stg to XYZ/XYZ.stg
- I recommend building the ANTLR tool 'in place'. Do not create a jar or compile/copy to a build directory. When you run it with 'java -cp path-to-src-dir ...' it will use the original *.stg file, which you'll edit a lot - so rebuilding the tool would be quite a PITA.
- Create a directory antlr-3.0/runtime/XYZ. Here you can put anything you need (no need to clone Java 1:1).
- Start with a simple lexer like:
lexer grammar T;
options { language = XYZ; }
ZERO: '0';
N.B: The name after the word "grammar" needs to be the same as the filename in which you save it, i.e. T.g.
- Look at the generated code and try to figure out which templates in XYZ.stg you have to port to get valid XYZ code. What I did, is to comment out the Java code in all templates replacing it with something like FIXME([number]). Then you fix the templates until no FIXME remains in the
output.
- You'll need a basic implementation of a character stream and base recognizer/lexer to get the example running. Just implement the methods that are actually needed to get the example running w/o errors.
- You'll either get the feeling "Wow, that was easy!" and move on (that happened to me) or "Eeek, what a pain!" and let someone else to the work.