feat: Read and show for Language.Scalie.Ast.Module

Previously, the read instance could be used to break invariants.

src/Data/Map/Implicit.hs

@@ -1,27 +1,41 @@
 {-# LANGUAGE Safe #-}
-{-# LANGUAGE TypeFamilies #-}
-{-# LANGUAGE StandaloneDeriving #-} -- specify instance contexts
+{-# LANGUAGE TypeFamilies #-} -- for KeyType
 {-# LANGUAGE FlexibleContexts #-} -- use non type-variable argument in instance head
 {-# LANGUAGE UndecidableInstances #-} -- use type family in instance head
+{-# LANGUAGE InstanceSigs #-}
 -- | A Map that derives the keys for the mapping from the items.
 
 module Data.Map.Implicit (ImplicitMap(), get, ImplicitKeyOf(..), empty) where
 import Data.Kind (Type, Constraint)
 import Data.Map (Map)
+import Text.Show (Show (show))
+import Data.String (String)
+import Control.Category ((.), Category (id))
 import Data.Map qualified as Map
-import Text.Show (Show)
-import Text.Read (Read)
+import Text.Read (Read (readPrec), ReadPrec)
+import Data.List qualified as List
+import Control.Arrow (Arrow ((&&&)))
+import Data.Functor ((<$>))
 import Data.Ord (Ord)
 
 type ImplicitMap :: Type -> Type
 type role ImplicitMap nominal
 newtype ImplicitMap v = ImplicitMap { get :: Map (KeyType v) v }
 
-deriving stock instance (Show (KeyType v), Show v) => Show (ImplicitMap v)
-deriving stock instance (Read (KeyType v), Ord (KeyType v), Read v) => Read (ImplicitMap v)
+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
 
 type ImplicitKeyOf :: Type -> Constraint
-
 class ImplicitKeyOf v where
   type KeyType v :: Type
   keyOf :: v -> KeyType v

src/Language/Scalie/Ast/Module.hs

@@ -10,18 +10,30 @@ import Language.Scalie.Ast.Definition (Definition)
 import Data.Map.Implicit (ImplicitMap)
 import Text.Show (Show)
 import Text.Read (Read)
-import Data.Text (Text)
-import Language.Scalie.Ast.Expression (Expression)
-import Language.Scalie.Domain.Type qualified as Scalie.Domain
-import Data.Ord (Ord)
 
 -- | A module groups multiple related definitions.
+--
+-- >>> import Data.Functor.Identity (Identity(..))
+-- >>> import Data.Map.Implicit qualified as ImplicitMap
+-- >>> Module (Identity ImplicitMap.empty)
+-- Module {definitions = Identity ImplicitMapElems []}
+--
+-- >>> import Data.Maybe (Maybe(..))
+-- >>> Module Nothing
+-- Module {definitions = Nothing}
+--
+-- >>> import Text.Read (readMaybe)
+-- >>> readMaybe "Module { definitions = Just (ImplicitMapElems []) }" :: Maybe (Module Maybe)
+-- Just (Module {definitions = Just ImplicitMapElems []})
+--
+-- >>> readMaybe "Module { definitions = Just (ImplicitMapElems [Definition { signature = Nothing, name = Just \"x\", body = Nothing } ]) }" :: Maybe (Module Maybe)
+-- Just (Module {definitions = Just ImplicitMapElems [Definition {signature = Nothing, name = Just "x", body = Nothing}]})
 
 type Module :: (Type -> Type) -> Type
 type role Module nominal
 data Module f = Module
-  { definitions :: ImplicitMap (Definition f)
+  { definitions :: f (ImplicitMap (Definition f))
   }
 
-deriving stock instance (Show (f Text), Show (f Expression), Show (f Scalie.Domain.Type)) => Show (Module f)
-deriving stock instance (Read (f Text), Ord (f Text), Read (f Expression), Read (f Scalie.Domain.Type)) => Read (Module f)
+deriving stock instance (Show (f (ImplicitMap (Definition f)))) => Show (Module f)
+deriving stock instance (Read (f (ImplicitMap (Definition f)))) => Read (Module f)