I'm definitely not an expert on this, but how the article describes it is you basically implement an AST with "execute" methods on its nodes. So that's just an

I'm definitely not an expert on this, but how the article describes it is you basically implement an AST with "execute" methods on its nodes. So that's just an interpreter that happens to use the Truffle framework to implement that AST. You can then implement continuations or TCO however you see fit. As I understand it, Graal is able to 'magically' turn that into a JIT. Again, I'm not an expert (I just read the article), but that seems very similar to how PyPy does it. The actual optimizations are different; PyPy uses tracing, while Graal uses Hotspot I think. Now, as you point out, you lose Java interop that way. However, you can imagine using Truffle + Graal to also build a similar interpreter for Java. For interop, your interpreter 'simply' has to merge in the AST for the Java interpreter (with its own 'execute' methods). As I understand it the RubyTruffle project uses a similar trick to do C interop.