Compiling Scheme using Java

Question

I was writing a Scheme interpreter (trying to be fully R5RS compatible) and it just struck me that compiling into VM opcodes would make it faster. (Correct me if I am wrong.) I can interpret the Scheme source code in the memory, but I am stuck at understanding code generation.

My question is: What patterns will be required to generate opcodes from a parse tree, for, say, the JVM or any other VM (or even a real machine)? And what, if any, will be the complications, advantages, or disadvantage of doing so?

Answer 1

For Scheme there will be two major complications related to JVM.

First, JVM does not support explicit tail calls annotations, therefore you won't be able to guarantee a proper tail recursion as required by R5RS (3.5) without resorting to an expensive mini-interpreter trick.

The second issue is with continuations support. JVM does not provide anything useful for implementing continuations, so again you're bound to use a mini-interpreter. Ie, each CPS trivial function should return a next closure, which will be then called by an infinite mini-interpreter loop.

But still there are many interesting optimisation possibilities. I'd recommend to take a look at Bigloo (there is a relatively fast JVM backend) and Kawa. For the general compilation techniques take a look at Scheme in 90 minutes .

And still, interpretation is a viable alternative to compilation (at least on JVM, due to its severe limitations and general inefficiency). See how SISC is implemented, it is quite an interesting and innovative approach.