Functional Reactive Programming with Reflex and CodeWorld

Background

A Gloss-model CodeWorld program

Intro to Reflex and FRP

CodeWorld’s Reflex Integration

import CodeWorld.Reflex
import Reflex
main = reflexOf $ \input -> return $
constDyn codeWorldLogo
reflexOf
:: (forall t m. (Reflex t, MonadHold t m, MonadFix m)
=> ReactiveInput t -> m (Dynamic t Picture))
-> IO ()
keyPress        :: ReactiveInput t -> Event   t Text
keyRelease :: ReactiveInput t -> Event t Text
textEntry :: ReactiveInput t -> Event t Text
pointerPress :: ReactiveInput t -> Event t Point
pointerRelease :: ReactiveInput t -> Event t Point
pointerPosition :: ReactiveInput t -> Dynamic t Point
pointerDown :: ReactiveInput t -> Dynamic t Bool
currentTime :: ReactiveInput t -> Dynamic t Double
timePassing :: ReactiveInput t -> Event t Double
import CodeWorld.Reflex
import Reflex
main :: IO ()
main = reflexOf $ \input -> return $ do
let angle = vectorDirection <$> pointerPosition input
rotated <$> angle <*> pure needle
needle = solidRectangle 6 0.3
{-# LANGUAGE OverloadedStrings #-}import CodeWorld.Reflex
import Control.Monad.Fix
import Reflex
main :: IO ()
main = reflexOf $ \input -> do
len <- needleLen input
let angle = vectorDirection <$> pointerPosition input
return $ rotated <$> angle <*> (needle <$> len)
needleLen
::
(Reflex t, MonadHold t m, MonadFix m)
=> ReactiveInput t -> m (Dynamic t Double)
needleLen input = do
let lenChange = fmapMaybe change (keyPress input)
foldDyn (+) 6 lenChange
where change "Up" = Just ( 1)
change "Down" = Just (-1)
change _ = Nothing
needle len = solidRectangle len 0.3

Traditional CodeWorld or Reflex?

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Chris Smith

Chris Smith

Software engineer, volunteer K-12 math and computer science teacher, author of the CodeWorld platform, amateur ring theorist, and Haskell enthusiast.