It wouldn't be a user-supplied binary. The user would provide C++ (say) source code. The service would compile the source code once to wasm say. A subset of the

It wouldn't be a user-supplied binary. The user would provide C++ (say) source code. The service would compile the source code once to wasm say. A subset of the standard library would be available. The service would spin up resources to run the wasm binary on demand from end-users. I am not proposing to try and make such a thing myself, but I'm hoping someone has done it. It would be widely useful. Programming languages are a dime a dozen but sharing simple programs written with them is problematic when there is such a disconnect between the I/O model of most programming languages plus their standard libraries and the realities of web architecture and plumbing. But adapting one to another is something people do. Web REPLs are a thing, I just want a web REPL taken to the next level. Surely it should be possible to do "Hello World" on the web.