Haxe backend in Haxe?

Question

I know that Haxe compiler is written in OCaml programming language, which is a quite good choice for compiler developer. However recently I found Luaxe project, that seems to be a full-featured Lua backend for Haxe and was developed as pure Haxe library. I looked at the code of the project and it is using some kind of macro magic to generate Lua source code at compile time. So I would like to ask is it possible to implement a full-featured backend in pure Haxe without digging into OCaml and rebuilding the compiler? If so is there any limitations? Is there any good article on how to implement a backend in pure Haxe?

Answer 1

It looks like the Luaxe project is using the setCustomJSGenerator API.

Basically, this runs as a macro, using --macro "setCustomJSGenerator(luaxe.LuaGenerator.use)" or something similar.

I've never built a custom backend myself, but you can use it either to do custom Javascript, or, to generate source code for a different language, which is done in each of these:

• Example JS Generator in the Haxe Standard Library: https://github.com/HaxeFoundation/haxe/blob/development/std/haxe/macro/ExampleJSGenerator.hx
• The Lua Generator from Luaxe: https://github.com/PeyTy/LuaXe/blob/master/luaxe/LuaGenerator.hx
• A Python code generator: https://github.com/frabbit/hx2python/blob/development/src/python/gen/PythonGenerator.hx
• A Dart code generator: https://bitbucket.org/AndrewVernon/hx2dart/src/203d61b299c88ca3a2b043335d92b71546ce1239/src/haxe/macro/DartGenerator.hx?at=development

You can look at each of these to get an idea of how the APIs work, they all have a fairly similar structure by the looks of things.

In terms of limitations, you would have to ask someone who has used this. I know the Python generator ended up being moved into the standard Haxe compiler, so is presumably in OCaml now - perhaps they found it too limiting? I'm not sure.

If you would like to know more about specific limitations of this approach, I would either ask on the Haxe mailing list, or contact the developers of the targets above and ask for them to share their wisdom.