9.3 A Virtual Machine for Guile

Enough about data—how does Guile run code?

Code is a grammatical production of a language. Sometimes these languages are implemented using interpreters: programs that run along-side the program being interpreted, dynamically translating the high-level code to low-level code. Sometimes these languages are implemented using compilers: programs that translate high-level programs to equivalent low-level code, and pass on that low-level code to some other language implementation. Each of these languages can be thought to be virtual machines: they offer programs an abstract machine on which to run.

Guile implements a number of interpreters and compilers on different language levels. For example, there is an interpreter for the Scheme language that is itself implemented as a Scheme program compiled to a bytecode for a low-level virtual machine shipped with Guile. That virtual machine is implemented by both an interpreter—a C program that interprets the bytecodes—and a compiler—a C program that dynamically translates bytecode programs to native machine code³⁶.

This section describes the language implemented by Guile’s bytecode virtual machine, as well as some examples of translations of Scheme programs to Guile’s VM.