tardis 0.4.4.0 → 0.5.0.1

raw patch · 9 files changed

Files

• ChangeLog.md +3/−0
• LICENSE +1/−1
• README.md +34/−0
• src/Control/Monad/Tardis.hs +4/−4
• src/Control/Monad/Tardis/Class.hs +9/−11
• src/Control/Monad/Trans/Tardis.hs +15/−17
• tardis.cabal +6/−7
• test/Example.hs +10/−11
• test/Main.hs +3/−1

@@ -0,0 +1,3 @@+* **0.5.0**:+  2024-01-15: Removed MonadTrans instance, replaced with liftTardisT+

@@ -1,4 +1,4 @@-Copyright (c) 2012, Dan Burton+Copyright (c) 2012-2026, Dan Burton  All rights reserved. 

@@ -0,0 +1,34 @@+# TardisT++![build status](https://github.com/DanBurton/tardis/actions/workflows/haskell.yml/badge.svg?branch=master)++The State monad allows you+to send information forwards to the future,+or to receive such information from the past.+The Reverse State monad allows you to do the reverse:+send information backwards to the past,+or receive information from the future. ++TardisT is a monad transformer+that provides state operations that allow you+to send information to both the future *and* the past,+as well as receive information from both directions.+It is isomorphic to a StateT on top of a ReverseStateT,+or vice-versa.++See test/Example.hs for an example.++----++This was inspired by Luke Palmer's blog post on+the "reverse state monad".++http://lukepalmer.wordpress.com/2008/08/10/mindfuck-the-reverse-state-monad/++See also:++http://panicsonic.blogspot.com/2007/12/backwards-state-or-power-of-laziness.html++----++(c) 2012-2026 Dan Burton

@@ -61,14 +61,14 @@     while setting the backwards-traveling state will affect the /past/.     Take a look at how Monadic bind is implemented for 'TardisT': -> m >>= f  = TardisT $ \ ~(bw, fw) -> do->   rec (x,  ~(bw'', fw' )) <- runTardisT m (bw', fw)->       (x', ~(bw' , fw'')) <- runTardisT (f x) (bw, fw')+> m >>= f  = TardisT $ \ ~(bw, fw) -> mdo+>   (x,  ~(bw'', fw' )) <- runTardisT m (bw', fw)+>   (x', ~(bw' , fw'')) <- runTardisT (f x) (bw, fw') >   return (x', (bw'', fw''))      Like the Reverse State monad transformer, TardisT's Monad instance     requires that the monad it transforms is an instance of MonadFix,-    as is evidenced by the use of @rec@.+    as is evidenced by the use of @mdo@.     Notice how the forwards-traveling state travels /normally/:     first it is fed to @m@, producing @fw'@, and then it is fed to @f x@,     producing @fw''@. The backwards-traveling state travels in the opposite

@@ -66,13 +66,12 @@    -- | A Tardis is merely a pure state transformation.   tardis :: ((bw, fw) -> (a, (bw, fw))) -> m a-  tardis f = do-    rec-      let (a, (future', past')) = f (future, past)-      sendPast future'-      past <- getPast-      future <- getFuture-      sendFuture past'+  tardis f = mdo+    let (a, (future', past')) = f (future, past)+    sendPast future'+    past <- getPast+    future <- getFuture+    sendFuture past'     return a  -- | Modify the forwards-traveling state@@ -83,10 +82,9 @@ -- | Modify the backwards-traveling state -- as it passes through from future to past. modifyBackwards :: MonadTardis bw fw m => (bw -> bw) -> m ()-modifyBackwards f = do-  rec-    sendPast (f x)-    x <- getFuture+modifyBackwards f = mdo+  sendPast (f x)+  x <- getFuture   return ()  -- | Retrieve a specific view of the forwards-traveling state.

@@ -1,4 +1,5 @@ {-# LANGUAGE RecursiveDo                     #-}+{-# LANGUAGE TupleSections #-}  -- | The data definition of a "TardisT" -- as well as its primitive operations,@@ -35,6 +36,7 @@      -- * Other   , mapTardisT+  , liftTardisT   , noState   ) where @@ -99,6 +101,10 @@ execTardis :: Tardis bw fw a -> (bw, fw) -> (bw, fw) execTardis t = runIdentity . execTardisT t +-- | An action in the underlying monad (or just functor, really)+-- can also be used in a Tardis by lifting it in.+liftTardisT :: (Functor m) => m a -> TardisT bw fw m a+liftTardisT m = TardisT $ \s -> fmap (,s) m  -- | A function that operates on the internal representation of a Tardis -- can also be used on a Tardis.@@ -119,28 +125,21 @@ -------------------------------------------------  instance MonadFix m => Monad (TardisT bw fw m) where-  return x = tardis $ \s -> (x, s)-  m >>= f  = TardisT $ \ ~(bw, fw) -> do-    rec (x,  ~(bw'', fw' )) <- runTardisT m (bw', fw)-        (x', ~(bw' , fw'')) <- runTardisT (f x) (bw, fw')+  m >>= f  = TardisT $ \ ~(bw, fw) -> mdo+    (x,  ~(bw'', fw' )) <- runTardisT m (bw', fw)+    (x', ~(bw' , fw'')) <- runTardisT (f x) (bw, fw')     return (x', (bw'', fw''))  instance MonadFix m => Functor (TardisT bw fw m) where   fmap = liftM  instance MonadFix m => Applicative (TardisT bw fw m) where-  pure = return+  pure x = tardis $ \s -> (x, s)   (<*>) = ap --instance MonadTrans (TardisT bw fw) where-  lift m = TardisT $ \s -> do-    x <- m-    return (x, s)- instance MonadFix m => MonadFix (TardisT bw fw m) where-  mfix f = TardisT $ \s -> do-    rec (x, s') <- runTardisT (f x) s+  mfix f = TardisT $ \s -> mdo+    (x, s') <- runTardisT (f x) s     return (x, s')  instance MFunctor (TardisT bw fw) where@@ -194,10 +193,9 @@ -- | Modify the backwards-traveling state -- as it passes through from future to past. modifyBackwards :: MonadFix m => (bw -> bw) -> TardisT bw fw m ()-modifyBackwards f = do-  rec-    sendPast (f x)-    x <- getFuture+modifyBackwards f = mdo+  sendPast (f x)+  x <- getFuture   return ()  

@@ -1,5 +1,5 @@ name:                tardis-version:             0.4.4.0+version:             0.5.0.1 synopsis:            Bidirectional state monad transformer homepage:            https://github.com/DanBurton/tardis bug-reports:         https://github.com/DanBurton/tardis/issues@@ -10,6 +10,8 @@ category:            Control build-type:          Simple cabal-version:       >=1.10+tested-with:         GHC == 9.14.1, GHC == 9.12.2, GHC == 9.10.3, GHC == 9.8.4, GHC == 9.6.7, GHC == 9.4.8+extra-source-files:  README.md, ChangeLog.md  description:   A Tardis is a combination of both a forwards and a backwards@@ -30,6 +32,7 @@   build-depends:       base >= 4.8 && < 5                      , mtl==2.*                      , mmorph==1.*+  ghc-options: -Wcompat -Wall -Wno-unused-imports  test-suite tardis-tests   default-language:  Haskell2010@@ -39,12 +42,8 @@   build-depends:     base >= 4.8 && < 5                    , tardis   other-modules:   Example+  ghc-options: -Wcompat -Wall -Wno-unrecognised-warning-flags -Wno-x-partial  source-repository head   type:     git-  location: git://github.com/DanBurton/tardis.git--source-repository this-  type:     git-  location: git://github.com/DanBurton/tardis.git-  tag:      tardis-0.4.1.0+  location: https://github.com/DanBurton/tardis.git

@@ -38,17 +38,16 @@     PreviousScores scores <- getPast     let score = head scores     return $ (finalFrameScore + score) : scores-  go (f : fs) = do-    rec-      sendPast $ NextThrows throws'-      PreviousScores scores <- getPast-      let score = head scores-      sendFuture $ PreviousScores (score' : scores)-      NextThrows ~(nextThrow1, nextThrow2) <- getFuture-      let (score', throws') = case f of-            Strike    -> (score + 10 + nextThrow1 + nextThrow2, (10, nextThrow1))-            Spare n   -> (score + 10 + nextThrow1,              (n, 10 - n))-            Frame n m -> (score + n + m,                        (n, m))+  go (f : fs) = mdo+    sendPast $ NextThrows throws'+    PreviousScores scores <- getPast+    let score = head scores+    sendFuture $ PreviousScores (score' : scores)+    NextThrows ~(nextThrow1, nextThrow2) <- getFuture+    let (score', throws') = case f of+          Strike    -> (score + 10 + nextThrow1 + nextThrow2, (10, nextThrow1))+          Spare n   -> (score + 10 + nextThrow1,              (n, 10 - n))+          Frame n m -> (score + n + m,                        (n, m))     go fs    finalFrameScore = case lastFrame game of

@@ -7,4 +7,6 @@     putStrLn $ "Expected: " <> show expectedScores     putStrLn $ "Actual: " <> show actualScores     exitFailure-  True -> exitSuccess+  True -> do+    putStrLn "Test passed."+    exitSuccess