jsonrpcserver uses the [OSlash](https://github.com/dbrattli/OSlash) package. From the [OSlash readme](https://github.com/dbrattli/OSlash/blob/c271c7633daf9d72393b419cfc9229e427e6a42a/README.md): > OSlash is intended to be a tutorial. For practical functional programming in Python in production environments you should use Expression instead.