feat: instances for Arbitrary

src/Data/Map/Implicit.hs

@@ -2,7 +2,8 @@
 {-# LANGUAGE TypeFamilies #-} -- for KeyType
 {-# LANGUAGE FlexibleContexts #-} -- use non type-variable argument in instance head
 {-# LANGUAGE UndecidableInstances #-} -- use type family in instance head
-{-# LANGUAGE InstanceSigs #-}
+{-# LANGUAGE InstanceSigs #-} -- type signature in Show and Read instance
+{-# LANGUAGE StandaloneDeriving #-} -- derive Eq
 -- | A Map that derives the keys for the mapping from the items.
 
 module Data.Map.Implicit (ImplicitMap(), get, ImplicitKeyOf(..), empty) where
@@ -14,26 +15,46 @@ import Control.Category ((.), Category (id))
 import Data.Map qualified as Map
 import Text.Read (Read (readPrec), ReadPrec)
 import Data.List qualified as List
-import Control.Arrow (Arrow ((&&&)))
+import Control.Arrow (Arrow ((&&&)), (>>>))
 import Data.Functor ((<$>))
 import Data.Ord (Ord)
+import Data.Eq (Eq)
+import Test.QuickCheck.Arbitrary (Arbitrary (arbitrary))
+import Test.QuickCheck.Gen (Gen)
+
+-- | This map will use the 'ImplicitKeyOf' class to compute the keys of the values.
 
 type ImplicitMap :: Type -> Type
 type role ImplicitMap nominal
 newtype ImplicitMap v = ImplicitMap { get :: Map (KeyType v) v }
 
+deriving stock instance (Eq v, Eq (KeyType v)) => Eq (ImplicitMap v)
+
+instance (Show v) => Show (ImplicitMap v) where
+  -- Serialize via the list of elements to avoid breaking invariants help by the map
+  show :: ImplicitMap v -> String
+  show = show . ImplicitMapElems . Map.elems . get
+
+instance (Read v, ImplicitKeyOf v, Ord (KeyType v)) => Read (ImplicitMap v) where
+  -- Serialize via the list of elements to avoid breaking invariants help by the map
+  readPrec :: ReadPrec (ImplicitMap v)
+  readPrec = ImplicitMap . Map.fromList . List.map (keyOf &&& id) . (\(ImplicitMapElems es) -> es) <$> readPrec
+
+instance (Arbitrary v, ImplicitKeyOf v, Ord (KeyType v)) => Arbitrary (ImplicitMap v) where
+  arbitrary :: Gen (ImplicitMap v)
+  arbitrary = fromList . (\(ImplicitMapElems es) -> es) <$> arbitrary
+
+
+-- | This is my helper type for the Show and Read instances of 'ImplicitMap'
+
 type ImplicitMapElems :: Type -> Type
 type role ImplicitMapElems representational
 newtype ImplicitMapElems v = ImplicitMapElems [v]
   deriving stock (Show, Read)
 
-instance (Show v) => Show (ImplicitMap v) where
-  show :: ImplicitMap v -> String
-  show = show . ImplicitMapElems . Map.elems . get
-
-instance (Read v, ImplicitKeyOf v, Ord (KeyType v)) => Read (ImplicitMap v) where
-  readPrec :: ReadPrec (ImplicitMap v)
-  readPrec = ImplicitMap . Map.fromList . List.map (keyOf &&& id) . (\(ImplicitMapElems es) -> es) <$> readPrec
+instance (Arbitrary v) => Arbitrary (ImplicitMapElems v) where
+  arbitrary :: Gen (ImplicitMapElems v)
+  arbitrary = ImplicitMapElems <$> arbitrary
 
 type ImplicitKeyOf :: Type -> Constraint
 class ImplicitKeyOf v where
@@ -42,3 +63,8 @@ class ImplicitKeyOf v where
 
 empty :: ImplicitMap v
 empty = ImplicitMap Map.empty
+
+fromList :: (ImplicitKeyOf v, Ord (KeyType v)) => [v] -> ImplicitMap v
+fromList = List.map (keyOf &&& id)
+  >>> Map.fromList
+  >>> ImplicitMap