salsa

A generic framework for on-demand, incrementalized computation.

Obligatory warning

Very much a WORK IN PROGRESS at this point. Ready for experimental use but expect frequent breaking changes.

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.

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.