salsa

A generic framework for on-demand, incrementalized computation.

Obligatory warning

Very much a WORK IN PROGRESS at this point.

Credits

This system is heavily inspired by adapton, glimmer, and rustc's query system. So credit goes to Eduard-Mihai Burtescu, Matthew Hammer, Yehuda Katz, and Michael Woerister.

Key idea

The key idea of salsa is that you define your program as a set of queries. Every query is used like function K -> V that maps from some key of type K to a value of type V. Queries come in two basic varieties:

• Inputs: the base inputs to your system. You can change these whenever you like.
• Functions: pure functions (no side effects) that transform your inputs into other values. The results of queries are memoized to avoid recomputing them a lot. When you make changes to the inputs, we'll figure out (fairly intelligently) when we can re-use these memoized values and when we have to recompute them.

Want to learn more?

To learn more about Salsa, try one of the following:

• read the heavily commented examples;
• check out the Salsa book;
  • 中文版
• watch one of our videos.

Getting in touch

The bulk of the discussion happens in the issues and pull requests, but we have a zulip chat as well.

Contributing

To create a release and publish to crates.io, follow the steps:

1. Update the version field in Cargo.toml.
2. Create a Git tag. The tag name must follow the format like "v*..".
3. Push. GitHub Actions will publish the crate to crates.io automatically.

lib.rs:

This crate defines various macro_rules macros used as part of Salsa's internal plumbing. These macros are re-exported under salsa::plumbing``. The procedural macros emit calls to these macro_rules` macros after doing error checking.

Using macro_rules macro definitions is generally more ergonomic and also permits true hygiene for local variables (sadly not items).

Currently the only way to have a macro that is re-exported from a submodule is to use multiple crates, hence the existence of this crate.