carboxyl is a library for functional reactive programming in Rust.

About

carboxyl provides primitives for functional reactive programming. It is heavily influenced by the Sodium libraries.

Functional reactive programming (FRP) is a paradigm that effectively fixes the issues present in the traditional observer pattern approach to event handling. It uses a set of compositional primitives to model the dependency graph of a reactive system. If you want to learn more about FRP, check out the Sodium blog.

This library provides two basic types: Stream and Cell. A stream is a discrete sequence of events, a cell is a container for values that change (discretely) over time.

API

The FRP primitive functions are mostly implemented as methods of the basic types to ease method chaining, except for lift2 which does not really belong to any type in particular.

In addition, the Sink type allows one to create a stream of events by dumping values into it. It is the only way to create an event from scratch, i.e. without using any of the other primitives.

Limitations

This library is fairly experimental and currently has some limitations:

• There are no strong guarantees about the order of events if used asynchronously. While events from the same source are guaranteed to arrive in order, events from different asynchronous sources arrive in an undefined order. This may be improved by introducing the notion of transactions in the internals, but I have not looked into that yet.
• The implementation relies on reference counting and vtable dispatch a lot. While this is necessary for it to work to some degree, I think it may be slower than it could potentially be. For reference, it takes about half a microsecond to dispatch an event through a simple dependency graph (see the benchmark in the source). While this is not too bad on its own, I suspect that in real-life applications, the event dispatch will suffer a lot of cache misses. I hope to find a better way to work around or with the limitations imposed by Rust's type system in the future.

Furthermore, it has not been used in any application yet. For all these reasons, I would be naturally very glad about feedback.