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https://github.com/aldanor/reactive-rs

Streams and broadcasts: functional reactive programming in Rust.
https://github.com/aldanor/reactive-rs

frp reactive rust stream

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Streams and broadcasts: functional reactive programming in Rust.

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README 

        
reactive-rs

===========



[![Build](https://api.travis-ci.org/aldanor/reactive-rs.svg)](https://travis-ci.org/aldanor/reactive-rs)

[![Crate](http://meritbadge.herokuapp.com/reactive-rs)](https://crates.io/crates/reactive-rs)

[![Docs](https://docs.rs/reactive-rs/badge.svg)](https://docs.rs/reactive-rs)



This crate provides the building blocks for functional reactive programming (FRP)

in Rust. It is inspired by

[carboxyl](https://crates.io/crates/carboxyl),

[frappe](https://crates.io/crates/frappe)

and [bidule](https://crates.io/crates/bidule) crates, and

various [ReactiveX](http://reactivex.io/) implementations.



### Documentation



[docs.rs/reactive-rs](https://docs.rs/reactive-rs)



### Purpose



The main use case of this library is to simplify creating efficient

computational DAGs (or computational trees, to be precise) that operate

on streams of values. It does not aim to replicate the entire galaxy of

ReactiveX operators, nor does it attempt to delve into

futures/concurrency territory.



What is a computational tree? First, there's the root at the top, that's

where the input values get fed into continuously. Then, we perform

computations on these values – each of which may yield zero,

one or more values that are sent further down. Some downstream

nodes may share their parents – for instance, `g(f(x))` and `h(f(x))`, where `x` is

the input and `f` is the intermediate transformation; in this case, we want

to make sure we don't have to recompute `f(x)` twice. Moreover, this

being Rust, we'd like to ensure we're not copying and cloning any values

needlessly, and we generally prefer things to be zero-cost/inlineable

when possible. Finally, there are leaves – these are observers, functions

that receive transform values and do something with them, likely recording

them somewhere or mutating the environment in some other way.



### Context



Streams, broadcasts and observers in this crate operate on pairs of

values: the *context* and the *element*. Context can be viewed as

optional metadata attached to the original value. Closures required in

methods like `.map()` only take one argument (the element) and are

expected to return a single value; this way, the element can be changed

without touching the context. This can be extremely convenient if you

need to access the original input value (or any "upstream" value) way

down the computation chain – this way you don't have to propagate

it explicitly.



Most stream/broadcast methods have an alternative "full" version that

operates on both context/element, with `_ctx` suffix.



### Usage example



Consider the following problem: we have an incoming stream of

buy/sell price pairs, and for each incoming event we would like to

compute how the current mid-price (the average between the two)

compares relatively to the minimum buy price and the maximum sell

price over the last three observations. Moreover, we would like to

skip the first few events in order to allow the buffer to fill up.



Here's one way we could do it (not the most ultimately efficient

way of solving this particular problem, but it serves quite well

to demonstrate the basic functionality of the crate):



```rust

use std::cell::Cell;

use std::f64;

use reactive_rs::*;



let min_rel = Cell::new(0.);

let max_rel = Cell::new(0.);



// create a broadcast of (buy, sell) pairs

let quotes = SimpleBroadcast::new();



// clone the broadcast so we can feed values to it later

let last = quotes.clone()

    // save the mid-price for later use

    .with_ctx_map(|_, &(buy, sell)| (buy + sell) / 2.)

    // cache the last three observations

    .last_n(3)

    // wait until the queue fills up

    .filter(|quotes| quotes.len() > 2)

    // share the output (slices of values)

    .broadcast();



// subscribe to the stream of slices

let min = last.clone()

    // compute min buy price

    .map(|p| p.iter().map(|q| q.0).fold(1./0., f64::min));

// subscribe to the stream of slices

let max = last.clone()

    // compute max sell price

    .map(|p| p.iter().map(|q| q.1).fold(-1./0., f64::max));



// finally, attach observers

min.subscribe_ctx(|p, min| min_rel.set(min / p));

max.subscribe_ctx(|p, max| max_rel.set(max / p));



quotes.send((100., 102.));

quotes.send((101., 103.));

assert_eq!((min_rel.get(), max_rel.get()), (0., 0.));

quotes.send((99., 101.));

assert_eq!((min_rel.get(), max_rel.get()), (0.99, 1.03));

quotes.send((97., 103.));

assert_eq!((min_rel.get(), max_rel.get()), (0.97, 1.03));

```



### License



The MIT License (MIT)



Copyright (c) 2018 Ivan Smirnov



Permission is hereby granted, free of charge, to any person obtaining a copy

of this software and associated documentation files (the "Software"), to deal

in the Software without restriction, including without limitation the rights

to use, copy, modify, merge, publish, distribute, sublicense, and/or sell

copies of the Software, and to permit persons to whom the Software is

furnished to do so, subject to the following conditions:



The above copyright notice and this permission notice shall be included in all

copies or substantial portions of the Software.



THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR

IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,

FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE

AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER

LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,

OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN THE

SOFTWARE.