Functional Reactive Programming by Gerold Meisinger

Functional reactive programming inSeminar Methods and Applications of Functional Programming Johannes Kepler University, Linz SS2012 by Gerold Meisinger

Background FH Hagenberg  Digital Media FRP diploma thesis Gamedev startup ”Modern Alchemists”

Types of programs Transformative Interactive Reactive

What is FRP? New paradigm Time-varying values Behavior a :: Time → a Hybrid modeling  Continous-time  Discrete events React to input

Paradigms (by Van Roy)

Similarities Paradigms Languages Dataflow  Esterel  Common Lisp/Cells  Lustre Temporal logic  Lucid Control theory  Signal ...  Synchrone  Simulink  Modelica  ...

Dataflow programming

FRP implementations Classic FRP  e.g. Fran, FrTime Push-pull FRP  e.g. Reactive Arrowized FRP  e.g. Yampa, Elera

Yampa examples Robotics GUIs Games Music synthesis Computer vision Networking ...

Classic game programminginterface IUpdateable void update( float elapsedTime )class GameObject : IUpdateable Vector3 position Vector3 velocity void update( float elapsedTime ) position += elapsedTime * velocity

Yampa semanticsSignal a :: Time → a Only used internallySF a b :: Signal a → Signal b SF … signal functiondata Event t = NoEvent | Event t

Yampa design goals Continous-time & discrete events Denotative semantics Dynamic structures Higher-orderness Avoid time and space leaks ⇒ Arrow typeclass Synchronous (vs concurrent)

Transformative f :: a → b

Interactive

Reactive

Temporal

Loop >

Loop > Processing (black-box)

Loop > Processing

Loop > Processing >

Loop > Processing > SF (BB)

Loop > Processing > SF

Loop > Processing > SF Mover

Loop > Processing > Mover

Loop > Processing >

Loop > Processing

Loop > Processing Player

Example game: Fran

Haskell typeclasses (by Yorgey)

Arrow classclass Arrow a where arr :: (b → c) → a b c (<<<) :: a b c → a c d → a b d first :: a b c → a (b, d) (c, d)+ lots of arrow lawsderive combinators: second, (***), (&&&)

Arrow combinators

Derived Arrow combinatorssecond :: (Arrow a) ⇒ a b c → a (d, b) (d, c)second f = arr swap >>> first f >>> arr swap where swap (a, b) = (b, a)(***) :: (Arrow a) ⇒ a b c → a b c → a (b, b) (c, c)f ⋆⋆⋆ g = first f >>> second g(&&&) :: (Arrow a) ⇒ a b c → a b c → a b (c, c)f &&& g = arr (λx → (x, x)) >>> (f *** g)

ArrowCircuitclass Arrow a ⇒ ArrowCircuit a where loop :: a (b, d) (c, d) → a b c init :: b → a b b+ even more laws

Arrow syntax myArrow x y = proc (a, b) → do c1 ← arrow1 −< a c2 ← arrow3 <<< arrow2 −< b c ← arrow4 −< (c1, c2) rec d ← arrow5 −< (c, b, d) returnA (c, d)

Signal function primitives

Events

Yampa switchswitch :: SF in (out, Event t) → (t → SF in out) → SF in out

Yampa parallel switchpSwitch :: Functor col => (forall sf. (in → col sf → col (ext, sf))) → col (SF ext out) → SF (in, col out) (Event mng) → (col (SF ext out) → mng → SF in (col out)) → SF in (col out)

Yampa switches immediate delayedonce switch dSwitchrecurring rSwitch drSwitchparallel broadcasted pSwitchB dpSwitchB rpSwitchB drpSwitchBparallel routed pSwitch dpSwitch rpSwitch drpSwitchcontinuation kSwitch dkSwitch

Processingreactimate :: IO (DTime, a) –- input → (b → IO ()) –- output → SF a b → IO ()

Game-Engine

Ongoing research Semantics  "Garbage collecting the semantics of FRP"  "Why classic FRP does not fit interactive behavior" Performance  Causal Commutative Arrows (CCA)  Concurrency  Arrow tuples vs. signal combining

Yampa alternatives ELM  Web runtime and IDE => converts to JavaScript http://elm-lang.org Reactive-Banana  Many examples http://apfelmus.nfshost.com

The Endhttp://lambdor.net

Functional Reactive Programming by Gerold Meisinger

by GeroldMeisinger on Jun 13, 2012

Accessibility

Categories

Upload Details

Usage Rights

Statistics

Functional Reactive Programming by Gerold Meisinger Presentation Transcript