Compile to WebAssembly using WebAssembly?

[xriss]

I'm looking for a language that can do the following...

Compile to wasm using WebAssembly, so eg inside javascript.

We setup a compiler wasm module, hand it a source string, compile it and get wasm bytecode out.

Then we take that bytecode and use it to setup a library module and do, well, much the same again, pass some data in process it and pull some data out. So normal sort of wasm library use but from source code compiled on the fly.

My hope is for all the compiler gubbins to be run inside a WebAssembly module in a slightly performant way without being huge and pretending it has an entire linux sub system inside...

The compiler looks like it is very self contained, so is this a use case that was considered?

It seems like it should be possible but involves some messing about with the compiler to get it setup more as a wasm library module. IE replace the CLI and IO of the highest level code with some exported library functions.

I'm really just asking here to check that this sounds reasonable and I haven't misunderstood anything?

[titzer]

Yes, this is possible and @diakopter has done it before.

Virgil has a wasm-wave target that compiles the minimal system interface to a simplified set of Wasm calls in (https://github.com/titzer/virgil/blob/master/rt/wasm-wave/wave.v3). If all of those calls are provided by JS, then anything that uses System.v3 will be able to run.

By default the compiler exposes a main function that takes command-line arguments, but with a little work it could expose other functions that e.g. take source as a string.

[diakopter]

Yep. Made an event-handling loop in the browser (I called it "bwave" and wrote the System and RI or whatever that corresponded) that actually was co-reentrant with the wasm memory. Definitely a toy experiment, but it ended up being a sort of REPL (made a terminal UI on a canvas and a pixel-blitting painter, so virgil code was painting the html5 canvas). Probably ended up re-discovering much of what the very-early emscripten runtime had, now that I think about it. A fun toy experiment.