Add show instances for AST type representation

CHANGELOG.md

@@ -14,6 +14,7 @@ and this project adheres to
 - `Type.Schema.implementations` contains a map from interfaces and objects to
   interfaces they implement.
 - Show instances for GraphQL type definitions in the `Type` modules.
+- Custom Show instances for the type representation in the AST.
 
 ## [0.11.0.0] - 2020-11-07
 ### Changed

src/Language/GraphQL/AST/Document.hs

@@ -281,7 +281,12 @@ data Type
     = TypeNamed Name
     | TypeList Type
     | TypeNonNull NonNullType
-    deriving (Eq, Show)
+    deriving Eq
+
+instance Show Type where
+    show (TypeNamed typeName) = Text.unpack typeName
+    show (TypeList listType) = concat ["[", show listType, "]"]
+    show (TypeNonNull nonNullType) = show nonNullType
 
 -- | Represents type names.
 type NamedType = Name
@@ -290,7 +295,11 @@ type NamedType = Name
 data NonNullType
     = NonNullTypeNamed Name
     | NonNullTypeList Type
-    deriving (Eq, Show)
+    deriving Eq
+
+instance Show NonNullType where
+    show (NonNullTypeNamed typeName) = '!' : Text.unpack typeName
+    show (NonNullTypeList listType) =  concat ["![", show listType, "]"]
 
 -- ** Directives