How do you glue languages together such that one can use multiple languages in a single source file? Our most recent concrete example has been to compose PHP and Python. We have a language composition editor which allows one to replace PHP functions with Python functions (with nice features like cross-language name scoping) within a single file. We then save these out and use PyPy-esque techniques to glue together multiple language VMs: we run them through a composed HP (Hippy) + Python (PyPy) RPython meta-tracing VM. Even with mixed source files, our performance is better than the stock PHP interpreter.