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* commit 'e007fc9bf7186eb4131b9a55dbc3bf6adc821040':
  purescript(reverse-state): feat: working reverse state
  purescript(reverse-state): feat: failed to use run
This commit is contained in:
prescientmoon 2024-10-12 03:48:14 +02:00
parent ef25c02f0e e007fc9bf7
commit 4810f54c4f
Signed by: prescientmoon
SSH key fingerprint: SHA256:WFp/cO76nbarETAoQcQXuV+0h7XJsEsOCI0UsyPIy6U
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/bower_components/
/node_modules/
/.pulp-cache/
/output/
/generated-docs/
/.psc-package/
/.psc*
/.purs*
/.psa*
/.spago

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{
"cSpell.words": [
"purescript"
]
}

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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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{-
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

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{-
Welcome to a Spago project!
You can edit this file as you like.
-}
{ name = "my-project"
, dependencies =
[ "console"
, "debug"
, "effect"
, "lazy"
, "profunctor"
, "psci-support"
, "transformers"
]
, packages = ./packages.dhall
, sources = [ "src/**/*.purs", "test/**/*.purs" ]
}

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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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/* 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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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
let
r = flip runReader "env" $ runBackwardsState state $ pure 0
log "State:"
logShow (snd r)
log "Result:"
logShow (force $ fst r)

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purescript/reverse-state/test/Main.purs Normal file
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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."