hot-eval

JIT-compiled expression evaluation for hot paths

What?

Essentially, it's a JIT-compiled toy language designed for single expressions.

Most expression evaluators convert a string to an AST, and then evaluate the AST directly. Instead, this crate:

1. Converts a string to an AST by using LALRPOP
2. Does semantic analysis on the AST to support types and custom variables/functions, creating an analysed AST (AAST)
3. Converts the AAST to machine code by using Inkwell

Why?

For most use-cases, you shouldn't use this crate. Use a crate like evalexpr, fasteval, meval, etc... However, if you need to evaluate the same expression repeatedly in a hot path, the expressions are trusted, and you value performance over anything else (including ergonomics and safety), then this crate might be suitable for your use-case.

For example, a good use-case would be to implement arbitrary predicates for huge input spaces.

A bad use-case would be to use this for a calculator, since you only need to evaluate the expression once (and the compilation cost is probably going to outweight the standard AST evaluation cost) and performance isn't critical.

Usage

For now, this crate isn't published, so you need to add it as a Git dependency. This crate will be published when it becomes more ergonomic and safe.

Make sure to have LLVM 21 installed, as it's a requirement for Inkwell. There are no plans to switch the backend compilation to Cranelift.

There is no documentation yet, and it will be written when the first version is published. If you want to use this project anyway, see main.rs for example code.

Acknowledgements

Some of the terminology in this crate was inpired by other projects:

• The concept of a Table to define the global context was inspired by Lua
• The concept of a Slab to define a fast interface was inspired by fasteval