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https://github.com/briancavalier/most-behave

Experimental continuous Behaviors for most.js
https://github.com/briancavalier/most-behave

functional-reactive-programming mostjs reactive-programming

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Experimental continuous Behaviors for most.js

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README 

        
# Behavior



**EXPERIMENTAL** Don't use this for anything real ... yet.



Continuous time-varying values for most.js.  Behaviors are the continuous complement to most.js discrete Event Streams, or, if you prefer, the "pull" complement to most.js "push" Event Streams.



## Try it



Feedback welcome via [gitter](https://gitter.im/cujojs/most), but seriously, don't use it for anything real yet.



```

npm i --save @briancavalier/most-behavior

```



## Behavior



A Behavior is a continuous value.  In contrast to an Event Stream which has discrete occurrences at particular instants in time, a Behavior's value is defined at all *real number* (not integer) values of time and may vary continuously (or not) over time.



Because they are defined for all real number values of time, a Behavior must be *sampled* to obtain its value at specific instants in time.  To sample a Behavior, pass it an Event Stream whose occurrences define all the points in time at which the behavior's value should be sampled.



Here's a simple example.  Note that because `clock` is "pull", it does no work at the instants between clicks, where it is *not* being sampled.



```js

import { time } from '@briancavalier/most-behavior'

import { click } from '@most/dom-event'



// A Behavior that always represents milliseconds since the application started

const clock = time



// Sample the clock each time the user clicks

const timeAtEachClick = sample(clock, click(document))

```



For now, [see the examples dir](examples) for more realistic code, how to run a `@most/core` app that integrates behaviors, etc.



## API



### Creating Behaviors



#### time :: Behavior number



A behavior that represents the current time in milliseconds since the application started.



#### always :: a → Behavior a



Create a Behavior whose value is always `a`.



#### step :: a → Stream a → Behavior a



Create a Behavior that starts with an initial value and updates to each new value in the Event Stream.



### Transforming Behaviors



#### map :: (a → b) → Behavior a → Behavior b



Apply a function to a Behavior at all points in time.



#### apply :: Behavior (a → b) → Behavior a → Behavior b



Apply a (time-varying) function to a Behavior at all points in time.



#### liftA2 :: (a → b → c) → Behavior a → Behavior b → Behavior c



Apply a function to 2 Behaviors at all points in time.



### Sampling Behaviors



#### sample :: Behavior a → Stream b → Stream a



Sample a Behavior's value at every occurrence of an Event Stream.



#### snapshot :: Behavior a → Stream b → Stream [a, b]



Sample a Behavior at every occurrence of an event, and compute a new event from the (event, sample) pair.



## Potential APIs



Potentially useful APIs we could add:



### when :: Behavior bool → Stream a → Stream a



Allow events only when a Behavior's value is `true`.



### accum :: a → Stream (a → a) → Behavior a



Create a Behavior with an initial value and an Event Stream carrying update functions.



### scanB :: (a → b → a) → a → Stream b → Behavior a



Like scan, but produces a Behavior.  Needs a helpful name ...



### scanB :: (a → b → Behavior a) → Behavior a → Stream b → Behavior b



Generalized scan for Behaviors.  When event occurs, sample Behavior, and apply a function that creates a new Behavior.  Somewhat like `switch`.  Needs a helpful name ...



### count :: Stream a → Behavior number



Create a Behavior representing the number of event occurrences.



### switch :: Behavior a → Stream (Behavior a) → Behavior a



Create a Behavior that acts like an initial Behavior and switches to act like each new Behavior that occurs in the Event Stream.