purescript-signal

Signal is a lightweight FRP-like library heavily inspired by the Elm Signal implementation. Where possible and sensible, it tries to maintain API equivalence with Elm.

See the Elm documentation for details on usage and principles.

PureScript Usage Patterns

PureScript depends on effects (specifically, the Eff monad) to manage side effects, where Elm's runtime generally manages them for you. purescript-signal provides the Signal.runSignal function for running effectful signals.

module Main where

import Control.Monad.Eff.Console
import Control.Monad.Eff
import Prelude
import Signal

hello :: Signal String
hello = constant "Hello Joe!"

helloEffect :: forall eff. Signal (Eff (console :: CONSOLE | eff) Unit)
helloEffect = hello ~> log

main = runSignal helloEffect

This simple example takes a constant signal which contains the string "Hello Joe!" and maps it over the Control.Monad.Eff.Console.log function, which has the type forall eff. String -> Eff (console :: CONSOLE | eff) Unit, thus taking the String content of the signal and turning it into an effect which logs the provided string to the user's console.

This gives us a Signal (Eff (console :: CONSOLE | eff) Unit). We use runSignal to take the signal of effects and run each effect in turn—in our case, just the one effect which prints "Hello Joe!" to the console.

API Documentation

• Module documentation on Pursuit

Usage Examples

• The canonical Elm Mario: https://github.com/michaelficarra/purescript-demo-mario
• Ponies: https://github.com/bodil/purescript-is-magic