Validate repeatable directives

src/Language/GraphQL/AST/DirectiveLocation.hs

@@ -1,6 +1,6 @@
 {-# LANGUAGE Safe #-}
 
--- | Various parts of a GraphQL document can be annotated with directives. 
+-- | Various parts of a GraphQL document can be annotated with directives.
 -- This module describes locations in a document where directives can appear.
 module Language.GraphQL.AST.DirectiveLocation
     ( DirectiveLocation(..)

src/Language/GraphQL/AST/Document.hs

@@ -380,7 +380,11 @@ instance Show NonNullType where
 --
 -- Directives begin with "@", can accept arguments, and can be applied to the
 -- most GraphQL elements, providing additional information.
-data Directive = Directive Name [Argument] Location deriving (Eq, Show)
+data Directive = Directive
+    { name :: Name
+    , arguments :: [Argument]
+    , location :: Location
+    } deriving (Eq, Show)
 
 -- * Type System
 

src/Language/GraphQL/AST/Encoder.hs

@@ -277,7 +277,7 @@ pipeList :: Foldable t => Formatter -> t Lazy.Text -> Lazy.Text
 pipeList Minified =  (" " <>) . Lazy.Text.intercalate " | " . toList
 pipeList (Pretty _) =  Lazy.Text.concat
     . fmap (("\n" <> indentSymbol <> "| ") <>)
-    . toList 
+    . toList
 
 enumValueDefinition :: Formatter -> Full.EnumValueDefinition -> Lazy.Text
 enumValueDefinition (Pretty _) enumValue =