With Racket, at least, the language encourages you to build very small pieces and assemble them into larger systems. It's fairly straightforward to connect the

With Racket, at least, the language encourages you to build very small pieces and assemble them into larger systems. It's fairly straightforward to connect the pieces together to share code. It does also encourage you to create mini-languages, but our approach was usually a large amount of modular Racket-y code with many fairly thin layers of syntax transformation used in each mini-language case. In that sense the problem of mutually incompatible languages didn't really arise (in fact, separate mini-languages coincided with separate usage areas quite well). Performance was an issue, and we generally needed to use the precompilation feature of Racket to be successful. The issue we ran into is that Racket's precompilation system produces fairly fragile and coupled binary files -- and is generally difficult to separate cleanly from the execution environment.