HotDrink implemented in Rust.
HotDrink lets you declaratively describe relations between values and how to enforce them, and can then automatically do so when the value of a variable changes.
This library is still very experimental, and the API may change.
Before getting started, here is a quick introduction to the terminology and how it works.
A component is a collection of variables and constraints between them that should be enforced.
A constraint represents a relation between variables we want to maintain.
It contains a collection of constraint satisfaction methods that describe the different ways to do so.
In the example, we want the relation a + b = c to hold at all times.
One way to enforce it is to re-compute a + b and set c to that value.
A constraint satisfaction method describes one way to enforce a constraint. It reads the values of some variables, and write to others.
```rust use hotdrink_rs::{component, ret, ConstraintSystem, event::Event};
// Define a set of variables and relations between them let mut component = component! { // Define the component component Component { // Define variables and their default values let a: i32 = 0, b: i32 = 0, c: i32 = 0; // Define a relation that must hold between variables. constraint Sum { // Provide three ways to enforce the constraint. // Only one of them will be selected, and which one // depends on which variable was edited last. abc(a: &i32, b: &i32) -> [c] = ret![a + *b]; acb(a: &i32, c: &i32) -> [b] = ret![c - a]; bca(b: &i32, c: &i32) -> [a] = ret![c - *b]; } } };
// Describe what should happen when a changes
component.subscribe("a", |event| match event {
Event::Pending => println!("A new value for a is being computed"),
Event::Ready(newvalue) => println!("New value for a: {}", newvalue),
Event::Error(errors) => println!("Computation for a failed: {:?}", errors),
}
);
// Change the value of a
component.set_variable("a", 3);
// Add the component to a constraint system. // One constraint system can contain many components. let mut cs = ConstraintSystem::new(); cs.add_component(component);
// Enforce all the constraints by selecting a method for each one, // and then executing the methods in topological order. cs.update(); ```
The project uses multiple nightly features, and must be built using nightly Rust.
I recommend using rustup, which can be downloaded here.
If an appropriate version of Rust is installed, it should be as simple as running the following:
bash
cargo build --release
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