spec

Part of the spec is a reference interpreter written in OCaml. Edit: link: https://github.com/WebAssembly/spec/tree/master/interpreter

WABT (https://github.com/WebAssembly/wabt/) and Binaryen (https://github.com/WebAssembly/binaryen) as well as the spec itself (https://github.com/WebAssembly/spec/tree/master/interpreter) all have interpreters for the WebAssembly language. What they don't have is the same import and export binding mechanisms that the JavaScript engines have. JS engines can bind wasm imports and exports with JS functions. The interpreters that exist today are great for testing implementations or compilers but don't have interesting capabilities to interact with an embedding environment. There have been a few experiments with non-JS embeddings (for example, implementations build on LLVM which could easily define bindings to native functions) but nothing really usable or productized yet.

As sunfish mentions below, this spec document is being conservative in describing things that are still being discussed. There are experimental implementations in Firefox, Chrome and Edge. See https://webassembly.github.io/demo/. There's more information about the current binary format here: https://github.com/WebAssembly/design/blob/master/BinaryEnco... There's a prototype spec interpreter here: https://github.com/WebAssembly/spec/tree/master/ml-proto There's a build waterfall testing multiple tools here: https://wasm-stat.us/console, including the experimental LLVM toolchain, the emscripten-wasm toolchain[0], binaryen[1], and sexpr-wasm[2]. WebAssembly is still under development, but I don't think it's fair to call it an early prototype. [disclaimer: I'm a WebAssembly contributor] [0]: https://github.com/kripken/emscripten/wiki/WebAssem

github.com/WebAssembly/sexpr-wasm-prototype github.com/WebAssembly/spec github.com/WebAssembly/design

This is not only about code size, but about efficiency and, more fundamentally, about what multiple values are. Are MRV just syntactic sugar around lists, a second-class mechanism ("tuples don't nest") for when you have zero-or-one return value, or a first-class feature which can benefit from the support of the runtime compiler? https://github.com/WebAssembly/spec/pull/215

The discussion on github also mentions Lua (https://github.com/WebAssembly/spec/pull/215#issuecomment-17...), though it is true that this is coming from a Common Lisp developer. From my point of view the feature is useful (efficient implementation without useless memory allocation) and the rebuttal looks slightly uninformed. There are discussions about coroutines (https://github.com/WebAssembly/design/blob/master/FutureFeat...) and more generally about low-level capabilities (https://extensiblewebmanifesto.org/). Among those, we can see in the design document (https://github.com/WebAssembly/design/blob/4dec2849ad6d79fae...) a "Multiple Return Values" section with a "TODO" placeholder text: it seems that WebAssembly people want to implement MRV.

The target prevails over the language. The implicit intent is to convert LLVM bitcode. "Please keep in mind that Wasm is not a user-facing language, it is a compilation target. To justify the extra complexity of this feature for its own sake, you would need to come up with convincing evidence that compilers would significantly benefit from it. I doubt that." https://github.com/WebAssembly/spec/pull/215#issuecomment-17...

You can follow webassembly standardization process here: https://github.com/WebAssembly/spec Look at prototype pull request in ChakraCore by one of our awesome engineer: https://github.com/Microsoft/ChakraCore/pull/63