Context: I'm experimenting with lowering D to a JITed language such as Lua or JavaScript for faster compilation to machine code, potential as a CTFE engine, and other reasons.

I want to cut in after opDispatch, after alias resolution, after alias this, after UFCS is reduced to a normal function call, and probably after template resolution.

Where (file) and how (methods, example code) do I get D's AST so I can traverse and lower it into another language's AST?

I imagine using a recursive stringification method to generate the code from the target language's AST as represented in the compiler, and replacing D's AST nodes with the target language's AST nodes, where the target language's nodes are subclasses of D nodes, pretending to be D language nodes.

On 2020-10-02 21:50, James Lu wrote:
> Context: I'm experimenting with lowering D to a JITed language such as Lua or JavaScript for faster compilation to machine code, potential as a CTFE engine, and other reasons.

IIRC, Adam D. Ruppe has worked on this. Outputting JavaScript code from D code.

> I want to cut in after opDispatch, after alias resolution, after alias this, after UFCS is reduced to a normal function call, and probably after template resolution.
> 
> Where (file) and how (methods, example code) do I get D's AST so I can traverse and lower it into another language's AST?

You probably want to starting doing things here [1]. This is after semantic analysis but before inlining.

> I imagine using a recursive stringification method to generate the code from the target language's AST as represented in the compiler, and replacing D's AST nodes with the target language's AST nodes, where the target language's nodes are subclasses of D nodes, pretending to be D language nodes.

Inheriting from D's AST nodes might be difficult. You want to use the existing visitors and either output the target language directly or build up your own AST. You probably want to inherit from this visitor [2].

Alternatively you can use DMD as a library and create a completely separate project which uses DMD as a dependency, here's an example [3].

[1] https://github.com/dlang/dmd/blob/5fda4ea088f70afb99818482e8482771758136a2/src/dmd/mars.d#L598

[2] https://github.com/dlang/dmd/blob/5fda4ea088f70afb99818482e8482771758136a2/src/dmd/visitor.d#L113

[3] https://github.com/jacob-carlborg/dlp

-- 
/Jacob Carlborg

On Saturday, 3 October 2020 at 07:33:41 UTC, Jacob Carlborg wrote:
> IIRC, Adam D. Ruppe has worked on this. Outputting JavaScript code from D code.

Yea, I played with it in 2011, but the compiler has changed since then, so I don't know how it is done anymore.

One of the post-semantic visitor classes surely though. None of those existed back then, but they actually should make it easier than it used to be. This is after compiler lowerings and error checks.