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purescript(reverse-state): feat: working reverse state

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Signed-off-by: prescientmoon <git@moonythm.dev>
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Matei Adriel 2020-11-17 12:16:14 +02:00 committed by prescientmoon
parent eb66415103
commit e007fc9bf7
Signed by: prescientmoon
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9 changed files with 513 additions and 124 deletions
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purescript/reverse-state/.vscode/settings.json vendored Normal file
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{
"cSpell.words": [
"purescript"
]
}

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purescript/reverse-state/LICENSE Normal file
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# Reverse state
My experiments with reverse state in purescript. Here's a short proof of concept
```purs
do
future <- get -- 4
modify \a -> a * 2
future' <- get -- 2
put 2
```

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purescript/reverse-state/spago.dhall
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{ name = "my-project"
, dependencies =
[ "console"
, "debug"
, "effect"
, "lazy"
, "profunctor"
, "psci-support"
, "run"
, "undefined"
, "transformers"
]
, packages = ./packages.dhall
, sources = [ "src/**/*.purs", "test/**/*.purs" ]

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purescript/reverse-state/src/BackwardsState.purs Normal file
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module BackwardsState where
import Prelude
import Control.MonadFix (class MonadFix, mfix)
import Data.Lazy (Lazy, force)
import Data.Lazy as Lazy
import Data.Newtype as Newtype
import Data.Profunctor.Strong (first)
import Data.Tuple (Tuple(..))
newtype BackwardsState s m a
= BackwardsState (Lazy s -> m (Tuple a (Lazy s)))
runBackwardsState :: forall s m a. Functor m => BackwardsState s m a -> Lazy s -> m (Tuple a s)
runBackwardsState (BackwardsState run) s = run s <#> map force
put :: forall s m. Monad m => s -> BackwardsState s m Unit
put s = BackwardsState \old -> pure $ Tuple unit (pure s)
putLazy :: forall s m. Monad m => Lazy s -> BackwardsState s m Unit
putLazy s = BackwardsState \old -> pure $ Tuple unit s
get :: forall m s. Monad m => BackwardsState s m (Lazy s)
get = BackwardsState \s -> pure $ Tuple s s
modify :: forall m s. Monad m => (s -> s) -> BackwardsState s m Unit
modify f = BackwardsState \s -> pure $ Tuple unit (f <$> s)
derive instance newtypeBackwardsState :: Newtype.Newtype (BackwardsState s m a) _
instance functorBS ∷ Functor m => Functor (BackwardsState s m) where
map = first >>> map >>> compose >>> Newtype.over BackwardsState
instance applicativeBackwardsState :: MonadFix m => Applicative (BackwardsState s m) where
pure a = BackwardsState (\s -> pure $ Tuple a s)
instance applyBackwardsState :: MonadFix m => Apply (BackwardsState s m) where
apply = ap
instance bindBackwardsState :: MonadFix m => Bind (BackwardsState s m) where
bind (BackwardsState run) f =
BackwardsState \state ->
_.results
<$> mfix \lazy -> do
(Tuple presentValue presentState) <-
run
$ Lazy.defer \_ -> force $ _.future $ lazy unit
(Tuple futureValue futureState) <- Newtype.unwrap (f presentValue) state
pure { results: Tuple futureValue presentState, future: futureState }
instance monadBackwardsState :: MonadFix m => Monad (BackwardsState s m)

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purescript/reverse-state/src/Control/MonadFix.js Normal file
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/* global exports, require */
"use strict";
//////////////////////////////////////////////////////////////////
// ATTRIBUTION
// monad-fix package is not on pursuit, so copied this file from -
// https://github.com/zrho/purescript-monad-fix/
//////////////////////////////////////////////////////////////////
// module Control.MonadFix
var message = "Control.MonadFix: Premature access to result of fixpoint computation."
// fixEffect :: forall eff a. ((Unit -> a) -> Eff eff a) -> Eff eff a
exports.fixEffect = function(f) {
return function() {
var result = null;
var ready = false;
result = f(function(u) {
if (!ready) throw new Error(message);
return result;
})();
ready = true;
return result;
}
}
// fixPure :: forall a. ((Unit -> a) -> a) -> a
exports.fixPure = function(f) {
return exports.fixEffect(function(a) { return function () { return f(a); }})();
}

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purescript/reverse-state/src/Control/MonadFix.purs Normal file
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module Control.MonadFix where
------------------------------------------------------------------
-- ATTRIBUTION
-- monad-fix package is not on pursuit, so copied this file from -
-- https://github.com/zrho/purescript-monad-fix/
------------------------------------------------------------------
import Prelude
import Control.Monad.RWS.Trans (RWST(..), RWSResult(..), runRWST)
import Control.Monad.Reader.Trans (ReaderT(..), runReaderT)
import Control.Monad.State.Trans (StateT(..), runStateT)
import Control.Monad.Writer.Trans (WriterT(..), runWriterT)
import Data.Identity (Identity(..))
import Data.Newtype (unwrap)
import Data.Tuple (fst)
import Effect (Effect)
foreign import fixEffect :: forall a. ((Unit -> a) -> Effect a) -> Effect a
foreign import fixPure :: forall a. ((Unit -> a) -> a) -> a
-- | Type class for monads that support fixpoints.
-- |
-- | `mfix f` runs `f` once with the eventual result of `f` as input. Make sure
-- | not to apply the supplied function until the computation returned; else
-- | a dynamic error will be thrown.
class (Monad m) <= MonadFix m where
mfix :: forall a. ((Unit -> a) -> m a) -> m a
instance monadFixRWST :: (Monoid w, MonadFix m) => MonadFix (RWST r w s m) where
mfix f = RWST \r s -> mfix \t -> runRWST (f \u -> case t u of RWSResult _ a _ -> a) r s
instance monadFixIdentity :: MonadFix Identity where
mfix = Identity <<< fixPure <<< (unwrap <<< _)
instance monadFixEff :: MonadFix Effect where
mfix = fixEffect
instance monadFixFunction :: MonadFix (Function r) where
mfix f r = fixPure (flip f r)
instance monadFixReaderT :: (MonadFix m) => MonadFix (ReaderT r m) where
mfix f = ReaderT \r -> mfix (flip runReaderT r <<< f)
instance monadFixStateT :: (MonadFix m) => MonadFix (StateT s m) where
mfix f = StateT \s -> mfix (flip runStateT s <<< f <<< (fst <<< _))
instance monadFixWriterT :: (MonadFix m, Monoid w) => MonadFix (WriterT w m) where
mfix f = WriterT $ mfix (runWriterT <<< f <<< (fst <<< _))

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purescript/reverse-state/src/Fix.purs
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module Fix where
import Prelude
import Control.Lazy (fix)
import Data.Either (Either(..))
import Data.Lazy (defer)
import Data.Lazy as Lazy
import Data.Symbol (class IsSymbol)
import Data.Traversable (sequence)
import Data.Tuple (Tuple)
import Prim.Row as Row
import Run (FProxy, Run, SProxy(..), VariantF)
import Run as Run
import Undefined (undefined)
data BackwardsState s a
= BackwardsState (s -> s) (s -> a)
derive instance functorBS ∷ Functor (BackwardsState s)
type BACKWARDS_STATE s
= FProxy (BackwardsState s)
_backwardsState ∷ SProxy "backwardsState"
_backwardsState = SProxy
liftBackwardsState ∷ forall s a r. BackwardsState s a → Run ( backwardsState ∷ BACKWARDS_STATE s | r ) a
liftBackwardsState = liftBackwardsStateAt _backwardsState
liftBackwardsStateAt ∷
forall t state a r label.
IsSymbol label ⇒
Row.Cons label (BACKWARDS_STATE state) t r ⇒
SProxy label →
BackwardsState state a →
Run r a
liftBackwardsStateAt = Run.lift
runBackwardsStateAt ::
forall label state rowWithState row a.
IsSymbol label ⇒
Row.Cons label (BACKWARDS_STATE state) row rowWithState ⇒
SProxy label →
state →
Run rowWithState a →
Run row (Tuple state a)
runBackwardsStateAt sym = undefined
where
handle ::
forall b.
VariantF rowWithState
(Run rowWithState b) ->
Either (BackwardsState state (Run rowWithState b)) (VariantF row (Run rowWithState b))
handle = Run.on sym Left Right
mkLoop ::
forall result acc b.
( acc ->
(BackwardsState state (Run rowWithState b)) ->
Run row result
) ->
(acc -> b -> result) -> acc -> Run rowWithState b -> Run row result
mkLoop handleState handleResult accumulated r = case Run.peel r of
Left peeled → case handle peeled of
Left bs → handleState accumulated bs
Right a' → Run.send a' >>= mkLoop handleState handleResult accumulated
Right result → pure $ handleResult accumulated result
loopState :: Lazy.Lazy state -> Run rowWithState Unit -> Run row (Lazy.Lazy state)
loopState = mkLoop handleState handleResult
where
{-
past = ...
present <- mkState future
future <- mkState past
-}
handleState :: state -> BackwardsState state (Run rowWithState Unit) -> Run row (Lazy.Lazy state)
handleState state (BackwardsState mkState mkValue) =
sequence do
(futureState :: Run _ _) <-
fix \m -> do
(futureState :: Run _ _) <- m
let
value :: Run _ _
value = mkValue <$> futureState
state' :: Run _ (Lazy.Lazy state)
state' = value >>= loopState state
pure
state'
pure (mkState <$> futureState)
handleResult = const
-- case Run.peel r of
-- Left a → case handle a of
-- Left (BackwardsState mkState _) → do
-- resultState <- loopState state
-- pure (mkState futureState)
-- Right a' → b >>= f
-- where
-- f = runBackwardsStateAt sym s
-- b = Run.send a'
-- Right a → pure (Tuple s a)
-- loop :: state -> Run rowWithState a -> Run row (Tuple state a)
-- loop s r = case Run.peel r of
-- Left a → case handle a of
-- Left (BackwardsState mkState mkValue) → do
-- let
-- value = mkValue resultState
-- (Tuple resultState resultValue) <- loop s value
-- pure $ Tuple (mkState futureState) resultValue
-- Right a' → b >>= f
-- where
-- f :: Run rowWithState a -> Run row (Tuple state a)
-- f = runBackwardsStateAt sym s
-- b :: Run row (Run rowWithState a)
-- b = Run.send a'
-- Right a → pure (Tuple s a)
a = 3

24
purescript/reverse-state/src/Main.purs
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module Main where
import Prelude
import BackwardsState (BackwardsState, get, modify, put, runBackwardsState)
import Control.Monad.Reader (Reader, runReader)
import Data.Lazy (Lazy, force)
import Data.Tuple (fst, snd)
import Effect (Effect)
import Effect.Class.Console (logShow)
import Effect.Console (log)
type LabM a
= BackwardsState Int (Reader String) (Lazy a)
state :: LabM Int
state = do
future <- get -- 4
modify \a -> a * 2
future' <- get -- 2
put 2
pure future
main :: Effect Unit
main = do
log "🍝"
let
r = flip runReader "env" $ runBackwardsState state $ pure 0
log "State:"
logShow (snd r)
log "Result:"
logShow (force $ fst r)