urbit/pkg/hs-urbit/lib/Arvo.hs

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module Arvo where
import ClassyPrelude
--------------------------------------------------------------------------------
data Event = Event
data Effect = Effect
data ArvoFn = MkArvoFn (Event -> ([Effect], ArvoFn))
data Arvo r
= Yield [Effect] (Event -> Arvo r)
| Pure r
-- Arvo is a Monad -------------------------------------------------------------
bind :: Arvo a -> (a -> Arvo b) -> Arvo b
bind (Pure x) f = f x
bind (Yield fx k) f = Yield fx (\ev -> bind (k ev) f)
instance Functor Arvo where
fmap f (Pure v) = Pure (f v)
fmap f (Yield fx cont) = Yield fx (fmap (fmap f) cont)
instance Applicative Arvo where
pure = Pure
mx <*> y = mx `bind` (\f -> f <$> y)
instance Monad Arvo where
(>>=) = bind
--------------------------------------------------------------------------------
yield :: [Effect] -> Arvo Event
yield fx = Yield fx Pure
example :: Arvo a
example = do
Event <- yield [Effect, Effect]
example