Fix dual monads

CHANGELOG.md

@@ -4,6 +4,10 @@
 
 - Refactor to avoid the noncanonical-monad-instances and star-is-type warnings
 
+- Add Eq and Show instances to DualListMonad
+
+- Fixes in documentation
+
 ## v1.1.0
 
 - Add the AtMost monad

package.yaml

@@ -1,7 +1,7 @@
 name:        exotic-list-monads
 synopsis:    Non-standard monads on lists and non-empty lists
 description: The usual list monad is only one of infinitely many ways to turn the list functor into a monad. The same applies to the usual non-empty list monad and the non-empty list functor. This library collects such non-standard "list" and "non-empty list" monads.
-version:     1.1.0
+version:     1.1.1
 license:     MIT
 copyright:   (c) 2020 Dylan McDermott, Maciej Piróg, Tarmo Uustalu
 author:      Maciej Piróg <maciej.adam.pirog@gmial.com>

src/Control/Monad/List/Exotic.hs

@@ -213,21 +213,17 @@ liftListFun f = wrap . f . unwrap
 -- | Every list monad has a dual, in which join is defined as
 --
 -- @
--- join . reverse . fmap reverse
+-- reverse . join . reverse . fmap reverse
 -- @
 --
--- (where join is the join of the original list monad), while return is
+-- (where join is the join of the original list monad).
 --
--- @
--- reverse . return
--- @
---
--- (where return is the return of the original list monad).
+-- return is the same as in the original monad.
 newtype DualListMonad m a = DualListMonad { unDualListMonad :: m a }
- deriving (Functor)
+ deriving (Functor, Show, Eq)
 
 instance (ListMonad m) => Applicative (DualListMonad m) where
-  pure  = DualListMonad . liftListFun reverse . pure
+  pure  = DualListMonad . pure
   (<*>) = ap
 
 instance (ListMonad m) => Monad (DualListMonad m) where

src/Control/Monad/List/NonEmpty/Exotic.hs

@@ -875,16 +875,12 @@ liftNEFun f = wrap . f . unwrap
 -- as
 --
 -- @
--- join . reverse . fmap reverse
+-- reverse . join . reverse . fmap reverse
 -- @
 --
--- (where join is the join of the original list monad), while return is
+-- (where join is the join of the original list monad).
 --
--- @
--- reverse . return
--- @
---
--- (where return is the return of the original list monad).
+-- return is the same as in the original monad.
 newtype DualNonEmptyMonad m a =
   DualNonEmptyMonad { unDualNonEmptyMonad :: m a }
  deriving (Functor, Show, Eq)

test/Control/Monad/List/ExoticSpec.hs

@@ -23,6 +23,7 @@ import Control.Monad (join)
 import Data.Proxy
 import GHC.Exts (IsList(..))
 
+deriving instance (Arbitrary (m a)) => Arbitrary (DualListMonad m a)
 deriving instance (Arbitrary a) => Arbitrary (GlobalFailure a)
 deriving instance (Arbitrary a) => Arbitrary (MazeWalk a)
 deriving instance (Arbitrary a) => Arbitrary (DiscreteHybrid a)
@@ -98,31 +99,38 @@ spec = do
     it "knows that last of non-empty is non-empty" $
       safeLast "Roy" `shouldBe` "y"
 
-  testMonad  "GlobalFailure"      (Proxy :: Proxy GlobalFailure)
+  testMonad  "GlobalFailure"  (Proxy :: Proxy GlobalFailure)
+  testMonad  "DualListMonad GlobalFailure" (Proxy :: Proxy (DualListMonad GlobalFailure))
   describe  "GlobalFailure is ZeroSemigroup" $ do
     it                                             "x <> eps       ==  eps"
       $ property $ \(x :: GlobalFailure Int)     -> x <> eps       ==  eps
     it                                             "eps <> x       ==  eps"
       $ property $ \(x :: GlobalFailure Int)     -> eps <> x       ==  eps
     it                                             "(x <> y) <> z  ==  x <> (y <> z)"
       $ property $ \(x :: GlobalFailure Int) y z -> (x <> y) <> z  ==  x <> (y <> z)
-  testMonad  "MazeWalk"           (Proxy :: Proxy MazeWalk)
+
+  testMonad  "MazeWalk" (Proxy :: Proxy MazeWalk)
+  testMonad  "DualListMonad MazeWalk" (Proxy :: Proxy (DualListMonad MazeWalk))
   describe  "MazeWalk is PalindromeAlgebra" $ do
     it                                        "x <> eps       ==  eps"
       $ property $ \(x :: MazeWalk Int)     -> x <> eps       ==  eps
     it                                        "eps <> x       ==  eps"
       $ property $ \(x :: MazeWalk Int)     -> eps <> x       ==  eps
     it                                        "(x <> y) <> z  ==  x <> (y <> (x <> z))"
       $ property $ \(x :: MazeWalk Int) y z -> (x <> y) <> z  ==  x <> (y <> (x <> z))
-  testMonad  "DiscreteHybrid"     (Proxy :: Proxy DiscreteHybrid)
+
+  testMonad  "DiscreteHybrid" (Proxy :: Proxy DiscreteHybrid)
+  testMonad  "DualListMonad DiscreteHybrid" (Proxy :: Proxy (DualListMonad DiscreteHybrid))
   describe  "DiscreteHybrid is LeaningAlgebra" $ do
     it                                              "x <> eps       ==  eps"
       $ property $ \(x :: DiscreteHybrid Int)     -> x <> eps       ==  eps
     it                                              "eps <> x       ==  x"
       $ property $ \(x :: DiscreteHybrid Int)     -> eps <> x       ==  x
     it                                              "(x <> y) <> z  ==  y <> z"
       $ property $ \(x :: DiscreteHybrid Int) y z -> (x <> y) <> z  ==  y <> z
-  testMonad  "ListUnfold"         (Proxy :: Proxy ListUnfold)
+
+  testMonad  "ListUnfold" (Proxy :: Proxy ListUnfold)
+  testMonad  "DualListMonad ListUnfold" (Proxy :: Proxy (DualListMonad ListUnfold))
   describe  "ListUnfold is SkewedAlgebra" $ do
     it                                          "x <> eps       ==  eps"
       $ property $ \(x :: ListUnfold Int)     -> x <> eps       ==  eps
@@ -131,17 +139,27 @@ spec = do
     it                                          "(x <> y) <> z  ==  eps"
       $ property $ \(x :: ListUnfold Int) y z -> (x <> y) <> z  ==  eps
 
-  testMonad  "Stutter 1"          (Proxy :: Proxy (Stutter 0))
-  testMonad  "Stutter 2"          (Proxy :: Proxy (Stutter 1))
+  testMonad  "Stutter 1"          (Proxy :: Proxy (Stutter 1))
+  testMonad  "Stutter 2"          (Proxy :: Proxy (Stutter 2))
   testMonad  "Stutter 5"          (Proxy :: Proxy (Stutter 5))
 
+  testMonad  "DualListMonad (Stutter 0)" (Proxy :: Proxy (DualListMonad (Stutter 0)))
+  testMonad  "DualListMonad (Stutter 1)" (Proxy :: Proxy (DualListMonad (Stutter 1)))
+  testMonad  "DualListMonad (Stutter 2)" (Proxy :: Proxy (DualListMonad (Stutter 2)))
+  testMonad  "DualListMonad (Stutter 5)" (Proxy :: Proxy (DualListMonad (Stutter 5)))
+
   testMonad  "StutterKeeper 0"    (Proxy :: Proxy (StutterKeeper 0))
   testMonad  "StutterKeeper 1"    (Proxy :: Proxy (StutterKeeper 1))
   testMonad  "StutterKeeper 2"    (Proxy :: Proxy (StutterKeeper 2))
   testMonad  "StutterKeeper 3"    (Proxy :: Proxy (StutterKeeper 3))
   testMonad  "StutterKeeper 4"    (Proxy :: Proxy (StutterKeeper 4))
   testMonad  "StutterKeeper 5"    (Proxy :: Proxy (StutterKeeper 5))
   testMonad  "StutterKeeper 10"   (Proxy :: Proxy (StutterKeeper 10))
+
+  testMonad  "DualListMonad (StutterKeeper 0)" (Proxy :: Proxy (DualListMonad (StutterKeeper 0)))
+  testMonad  "DualListMonad (StutterKeeper 1)" (Proxy :: Proxy (DualListMonad (StutterKeeper 1)))
+  testMonad  "DualListMonad (StutterKeeper 2)" (Proxy :: Proxy (DualListMonad (StutterKeeper 2)))
+  testMonad  "DualListMonad (StutterKeeper 5)" (Proxy :: Proxy (DualListMonad (StutterKeeper 5)))
 
   testMonad  "StutterStutter 0 0" (Proxy :: Proxy (StutterStutter 0 0))
   testMonad  "StutterStutter 0 1" (Proxy :: Proxy (StutterStutter 0 1))
@@ -192,9 +210,16 @@ spec = do
 
   testMonad  "ShortStutterKeeper 0 0" (Proxy :: Proxy (ShortStutterKeeper 0 0))
   testMonad  "ShortStutterKeeper 0 1" (Proxy :: Proxy (ShortStutterKeeper 0 1))
-  testMonad  "ShortStutterKeeper 0 1" (Proxy :: Proxy (ShortStutterKeeper 1 0))
+  testMonad  "ShortStutterKeeper 1 0" (Proxy :: Proxy (ShortStutterKeeper 1 0))
   testMonad  "ShortStutterKeeper 1 1" (Proxy :: Proxy (ShortStutterKeeper 1 1))
   testMonad  "ShortStutterKeeper 5 3" (Proxy :: Proxy (ShortStutterKeeper 5 3))
   testMonad  "ShortStutterKeeper 3 5" (Proxy :: Proxy (ShortStutterKeeper 3 5))
 
+  testMonad  "DualListMonad (ShortStutterKeeper 0 0)" (Proxy :: Proxy (DualListMonad (ShortStutterKeeper 0 0)))
+  testMonad  "DualListMonad (ShortStutterKeeper 0 1)" (Proxy :: Proxy (DualListMonad (ShortStutterKeeper 0 1)))
+  testMonad  "DualListMonad (ShortStutterKeeper 1 0)" (Proxy :: Proxy (DualListMonad (ShortStutterKeeper 1 0)))
+  testMonad  "DualListMonad (ShortStutterKeeper 1 1)" (Proxy :: Proxy (DualListMonad (ShortStutterKeeper 1 1)))
+  testMonad  "DualListMonad (ShortStutterKeeper 5 3)" (Proxy :: Proxy (DualListMonad (ShortStutterKeeper 5 3)))
+  testMonad  "DualListMonad (ShortStutterKeeper 3 5)" (Proxy :: Proxy (DualListMonad (ShortStutterKeeper 3 5)))
+