From eb6641510340ec1407773b64eb3aa6d016428e62 Mon Sep 17 00:00:00 2001 From: Matei Adriel Date: Mon, 16 Nov 2020 13:26:43 +0200 Subject: [PATCH 1/2] purescript(reverse-state): feat: failed to use run Signed-off-by: prescientmoon --- purescript/reverse-state/.gitignore | 10 ++ purescript/reverse-state/packages.dhall | 128 ++++++++++++++++++++++++ purescript/reverse-state/spago.dhall | 17 ++++ purescript/reverse-state/src/Fix.purs | 120 ++++++++++++++++++++++ purescript/reverse-state/src/Main.purs | 10 ++ purescript/reverse-state/test/Main.purs | 11 ++ 6 files changed, 296 insertions(+) create mode 100644 purescript/reverse-state/.gitignore create mode 100644 purescript/reverse-state/packages.dhall create mode 100644 purescript/reverse-state/spago.dhall create mode 100644 purescript/reverse-state/src/Fix.purs create mode 100644 purescript/reverse-state/src/Main.purs create mode 100644 purescript/reverse-state/test/Main.purs diff --git a/purescript/reverse-state/.gitignore b/purescript/reverse-state/.gitignore new file mode 100644 index 0000000..30efe19 --- /dev/null +++ b/purescript/reverse-state/.gitignore @@ -0,0 +1,10 @@ +/bower_components/ +/node_modules/ +/.pulp-cache/ +/output/ +/generated-docs/ +/.psc-package/ +/.psc* +/.purs* +/.psa* +/.spago diff --git a/purescript/reverse-state/packages.dhall b/purescript/reverse-state/packages.dhall new file mode 100644 index 0000000..d21b708 --- /dev/null +++ b/purescript/reverse-state/packages.dhall @@ -0,0 +1,128 @@ +{- +Welcome to your new Dhall package-set! + +Below are instructions for how to edit this file for most use +cases, so that you don't need to know Dhall to use it. + +## Warning: Don't Move This Top-Level Comment! + +Due to how `dhall format` currently works, this comment's +instructions cannot appear near corresponding sections below +because `dhall format` will delete the comment. However, +it will not delete a top-level comment like this one. + +## Use Cases + +Most will want to do one or both of these options: +1. Override/Patch a package's dependency +2. Add a package not already in the default package set + +This file will continue to work whether you use one or both options. +Instructions for each option are explained below. + +### Overriding/Patching a package + +Purpose: +- Change a package's dependency to a newer/older release than the + default package set's release +- Use your own modified version of some dependency that may + include new API, changed API, removed API by + using your custom git repo of the library rather than + the package set's repo + +Syntax: +Replace the overrides' "{=}" (an empty record) with the following idea +The "//" or "⫽" means "merge these two records and + when they have the same value, use the one on the right:" +------------------------------- +let overrides = + { packageName = + upstream.packageName // { updateEntity1 = "new value", updateEntity2 = "new value" } + , packageName = + upstream.packageName // { version = "v4.0.0" } + , packageName = + upstream.packageName // { repo = "https://www.example.com/path/to/new/repo.git" } + } +------------------------------- + +Example: +------------------------------- +let overrides = + { halogen = + upstream.halogen // { version = "master" } + , halogen-vdom = + upstream.halogen-vdom // { version = "v4.0.0" } + } +------------------------------- + +### Additions + +Purpose: +- Add packages that aren't already included in the default package set + +Syntax: +Replace the additions' "{=}" (an empty record) with the following idea: +------------------------------- +let additions = + { package-name = + { dependencies = + [ "dependency1" + , "dependency2" + ] + , repo = + "https://example.com/path/to/git/repo.git" + , version = + "tag ('v4.0.0') or branch ('master')" + } + , package-name = + { dependencies = + [ "dependency1" + , "dependency2" + ] + , repo = + "https://example.com/path/to/git/repo.git" + , version = + "tag ('v4.0.0') or branch ('master')" + } + , etc. + } +------------------------------- + +Example: +------------------------------- +let additions = + { benchotron = + { dependencies = + [ "arrays" + , "exists" + , "profunctor" + , "strings" + , "quickcheck" + , "lcg" + , "transformers" + , "foldable-traversable" + , "exceptions" + , "node-fs" + , "node-buffer" + , "node-readline" + , "datetime" + , "now" + ] + , repo = + "https://github.com/hdgarrood/purescript-benchotron.git" + , version = + "v7.0.0" + } + } +------------------------------- +-} + + +let upstream = + https://github.com/purescript/package-sets/releases/download/psc-0.13.8-20201021/packages.dhall sha256:55ebdbda1bd6ede4d5307fbc1ef19988c80271b4225d833c8d6fb9b6fb1aa6d8 + +let overrides = {=} + +let additions = {=} + +in upstream // overrides // additions diff --git a/purescript/reverse-state/spago.dhall b/purescript/reverse-state/spago.dhall new file mode 100644 index 0000000..a46c992 --- /dev/null +++ b/purescript/reverse-state/spago.dhall @@ -0,0 +1,17 @@ +{- +Welcome to a Spago project! +You can edit this file as you like. +-} +{ name = "my-project" +, dependencies = + [ "console" + , "effect" + , "lazy" + , "profunctor" + , "psci-support" + , "run" + , "undefined" + ] +, packages = ./packages.dhall +, sources = [ "src/**/*.purs", "test/**/*.purs" ] +} diff --git a/purescript/reverse-state/src/Fix.purs b/purescript/reverse-state/src/Fix.purs new file mode 100644 index 0000000..92e7b0f --- /dev/null +++ b/purescript/reverse-state/src/Fix.purs @@ -0,0 +1,120 @@ +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 diff --git a/purescript/reverse-state/src/Main.purs b/purescript/reverse-state/src/Main.purs new file mode 100644 index 0000000..5c18dca --- /dev/null +++ b/purescript/reverse-state/src/Main.purs @@ -0,0 +1,10 @@ +module Main where + +import Prelude + +import Effect (Effect) +import Effect.Console (log) + +main :: Effect Unit +main = do + log "🍝" diff --git a/purescript/reverse-state/test/Main.purs b/purescript/reverse-state/test/Main.purs new file mode 100644 index 0000000..f91f98c --- /dev/null +++ b/purescript/reverse-state/test/Main.purs @@ -0,0 +1,11 @@ +module Test.Main where + +import Prelude + +import Effect (Effect) +import Effect.Class.Console (log) + +main :: Effect Unit +main = do + log "🍝" + log "You should add some tests." From e007fc9bf7186eb4131b9a55dbc3bf6adc821040 Mon Sep 17 00:00:00 2001 From: Matei Adriel Date: Tue, 17 Nov 2020 12:16:14 +0200 Subject: [PATCH 2/2] purescript(reverse-state): feat: working reverse state Signed-off-by: prescientmoon --- .../reverse-state/.vscode/settings.json | 5 + purescript/reverse-state/LICENSE | 339 ++++++++++++++++++ purescript/reverse-state/README.md | 11 + purescript/reverse-state/spago.dhall | 4 +- .../reverse-state/src/BackwardsState.purs | 51 +++ .../reverse-state/src/Control/MonadFix.js | 33 ++ .../reverse-state/src/Control/MonadFix.purs | 50 +++ purescript/reverse-state/src/Fix.purs | 120 ------- purescript/reverse-state/src/Main.purs | 24 +- 9 files changed, 513 insertions(+), 124 deletions(-) create mode 100644 purescript/reverse-state/.vscode/settings.json create mode 100644 purescript/reverse-state/LICENSE create mode 100644 purescript/reverse-state/README.md create mode 100644 purescript/reverse-state/src/BackwardsState.purs create mode 100644 purescript/reverse-state/src/Control/MonadFix.js create mode 100644 purescript/reverse-state/src/Control/MonadFix.purs delete mode 100644 purescript/reverse-state/src/Fix.purs diff --git a/purescript/reverse-state/.vscode/settings.json b/purescript/reverse-state/.vscode/settings.json new file mode 100644 index 0000000..a90708f --- /dev/null +++ b/purescript/reverse-state/.vscode/settings.json @@ -0,0 +1,5 @@ +{ + "cSpell.words": [ + "purescript" + ] +} \ No newline at end of file diff --git a/purescript/reverse-state/LICENSE b/purescript/reverse-state/LICENSE new file mode 100644 index 0000000..1d258c7 --- /dev/null +++ b/purescript/reverse-state/LICENSE @@ -0,0 +1,339 @@ + GNU GENERAL PUBLIC LICENSE + Version 2, June 1991 + + Copyright (C) 1989, 1991 Free Software Foundation, Inc., + 51 Franklin Street, Fifth Floor, Boston, MA 02110-1301 USA + Everyone is permitted to copy and distribute verbatim copies + of this license document, but changing it is not allowed. + + Preamble + + The licenses for most software are designed to take away your +freedom to share and change it. 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Of course, the commands you use may +be called something other than `show w' and `show c'; they could even be +mouse-clicks or menu items--whatever suits your program. + +You should also get your employer (if you work as a programmer) or your +school, if any, to sign a "copyright disclaimer" for the program, if +necessary. Here is a sample; alter the names: + + Yoyodyne, Inc., hereby disclaims all copyright interest in the program + `Gnomovision' (which makes passes at compilers) written by James Hacker. + + , 1 April 1989 + Ty Coon, President of Vice + +This General Public License does not permit incorporating your program into +proprietary programs. If your program is a subroutine library, you may +consider it more useful to permit linking proprietary applications with the +library. If this is what you want to do, use the GNU Lesser General +Public License instead of this License. diff --git a/purescript/reverse-state/README.md b/purescript/reverse-state/README.md new file mode 100644 index 0000000..22b5a32 --- /dev/null +++ b/purescript/reverse-state/README.md @@ -0,0 +1,11 @@ +# 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 +``` diff --git a/purescript/reverse-state/spago.dhall b/purescript/reverse-state/spago.dhall index a46c992..eb577b7 100644 --- a/purescript/reverse-state/spago.dhall +++ b/purescript/reverse-state/spago.dhall @@ -5,12 +5,12 @@ You can edit this file as you like. { name = "my-project" , dependencies = [ "console" + , "debug" , "effect" , "lazy" , "profunctor" , "psci-support" - , "run" - , "undefined" + , "transformers" ] , packages = ./packages.dhall , sources = [ "src/**/*.purs", "test/**/*.purs" ] diff --git a/purescript/reverse-state/src/BackwardsState.purs b/purescript/reverse-state/src/BackwardsState.purs new file mode 100644 index 0000000..cae9d5a --- /dev/null +++ b/purescript/reverse-state/src/BackwardsState.purs @@ -0,0 +1,51 @@ +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) diff --git a/purescript/reverse-state/src/Control/MonadFix.js b/purescript/reverse-state/src/Control/MonadFix.js new file mode 100644 index 0000000..4573ee5 --- /dev/null +++ b/purescript/reverse-state/src/Control/MonadFix.js @@ -0,0 +1,33 @@ +/* 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); }})(); +} diff --git a/purescript/reverse-state/src/Control/MonadFix.purs b/purescript/reverse-state/src/Control/MonadFix.purs new file mode 100644 index 0000000..6c6c21f --- /dev/null +++ b/purescript/reverse-state/src/Control/MonadFix.purs @@ -0,0 +1,50 @@ +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 <<< _)) diff --git a/purescript/reverse-state/src/Fix.purs b/purescript/reverse-state/src/Fix.purs deleted file mode 100644 index 92e7b0f..0000000 --- a/purescript/reverse-state/src/Fix.purs +++ /dev/null @@ -1,120 +0,0 @@ -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 diff --git a/purescript/reverse-state/src/Main.purs b/purescript/reverse-state/src/Main.purs index 5c18dca..4ef5c3d 100644 --- a/purescript/reverse-state/src/Main.purs +++ b/purescript/reverse-state/src/Main.purs @@ -1,10 +1,30 @@ 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)