EmJay is a very simple JIT interpreter that can execute a very simple programming language. It is a toy project, created only for learning purposes and has absolutely zero practical applications.
The language has the following limitations and features:
- it only has one data type -
i64; - it supports only the basic algebraic operations;
- it has no control flow statements (i.e. no
ifor loops); - it allows variable declaration, nested scopes, and function calls;
- it supports aarch64 as a backend (i.e. Apple silicon). There's also an x64_linux backend, but it's not complete and basically not maintained.
It's a glorified calculator, basically.
- it parses the input string and generates an AST;
- it processes the AST and generates and IR in SSA;
- it then performs some basic optimization on the IR;
- it then generates machine code from the IR;
- and finally it executes it and performs the computation.
It uses the pest parser library for the parsing, but the rest was all implemented by hand - I did not rely on things like llvm or cranelift. As a result, it generates pretty mediocre machine code, but it was a very useful learning exercise.
This is an example of some valid syntax:
fn main() {
let v = 1000;
return v + f(3, 2, 1);
}
fn f(x, y, z) {
return x * 100 + y * 10 + (g(z) + z) * 2;
}
fn g(z) {
return z + 1;
}
For more details, check out my blog post on https://andreabergia.com/blog/2025/02/emjay-a-simple-jit-that-does-math/