[jacobolus]

Is there (or are there any plans to add) a WebAssembly -> asm.js compiler, so that I can write some code by hand in WebAssembly and still get it to run fast in old browsers? Or are there features of WebAssembly that would be impossible to add in asm.js?

The reason I ask is that asm.js is really painful and cumbersome to write by hand and wasm seems substantially nicer, but I only have small bits of numerical hot loops which I want to use wasm/asm.js for, and I have no desire to bring a bunch of code written in C into my little project.

[erickt]

Yes there is. That's the wasm2asm project Alon mentioned in the post.

[jacobolus]

Whoops, I read right past that line. :-) Thanks, I’ll take a look.

For anyone interested, the code is in wasm2asm.h: https://github.com/WebAssembly/binaryen/blob/master/src/wasm...

[azakai]

I agree asm.js isn't fun to write by hand, but wasm is also primarily a compiler target. You might not necessarily find it easier to write (its text format isn't defined or even sketched out yet, so it's impossible to guess).

If you just want to compile a few small functions with hot loops, it might be easiest to write them in C, and use a new option in emscripten that makes it easy to get just the output from those functions (no libc, no runtime support, etc.), see

https://gist.github.com/kripken/910bfe8524bdaeb7df9a

and

https://gist.github.com/wycats/4845049dcf0f6571387a

[jacobolus]

Both of the proposed syntaxes I’ve seen for wasm text format (an s-expression syntax and a C-like syntax) seem pretty nice. The sexp format in particular seems like it would be a great target for simple bits of purpose-specific code generation (for code that doesn’t need a “compiler” per se).