1 files changed, 15 insertions, 17 deletions
diff --git a/src/Language/GraphQL/Validate/Rules.hs b/src/Language/GraphQL/Validate/Rules.hs
index 2d7adba..e60d39d 100644
--- a/src/Language/GraphQL/Validate/Rules.hs
+++ b/src/Language/GraphQL/Validate/Rules.hs
@@ -50,14 +50,15 @@ import Control.Monad.Trans.Class (MonadTrans(..))
 import Control.Monad.Trans.Reader (ReaderT(..), ask, asks, mapReaderT)
 import Control.Monad.Trans.State (StateT, evalStateT, gets, modify)
 import Data.Bifunctor (first)
-import Data.Foldable (find, fold, foldl', toList)
+import Data.Foldable (Foldable(..), find)
 import qualified Data.HashMap.Strict as HashMap
 import Data.HashMap.Strict (HashMap)
 import Data.HashSet (HashSet)
 import qualified Data.HashSet as HashSet
-import Data.List (groupBy, sortBy, sortOn)
+import Data.List (sortBy)
 import Data.Maybe (fromMaybe, isJust, isNothing, mapMaybe)
 import Data.List.NonEmpty (NonEmpty(..))
+import qualified Data.List.NonEmpty as NonEmpty
 import Data.Ord (comparing)
 import Data.Sequence (Seq(..), (|>))
 import qualified Data.Sequence as Seq
@@ -253,14 +254,16 @@ findDuplicates :: (Full.Definition -> [Full.Location] -> [Full.Location])
     -> Full.Location
     -> String
     -> RuleT m
-findDuplicates filterByName thisLocation errorMessage = do
-    ast' <- asks ast
-    let locations' = foldr filterByName [] ast'
-    if length locations' > 1 && head locations' == thisLocation
-        then pure $ error' locations'
-        else lift mempty
+findDuplicates filterByName thisLocation errorMessage =
+    asks ast >>= go . foldr filterByName []
   where
-    error' locations' = Error 
+    go locations' =
+        case locations' of
+            headLocation : otherLocations -- length locations' > 1
+                | not $ null otherLocations
+                , headLocation == thisLocation -> pure $ makeError locations'
+            _ -> lift mempty
+    makeError locations' = Error
         { message = errorMessage
         , locations = locations'
         }
@@ -536,11 +539,6 @@ uniqueDirectiveNamesRule = DirectivesRule
     extract (Full.Directive directiveName _ location') =
         (directiveName, location')
 
-groupSorted :: forall a. (a -> Text) -> [a] -> [[a]]
-groupSorted getName = groupBy equalByName . sortOn getName
-  where
-    equalByName lhs rhs = getName lhs == getName rhs
-
 filterDuplicates :: forall a
     . (a -> (Text, Full.Location))
     -> String
@@ -549,12 +547,12 @@ filterDuplicates :: forall a
 filterDuplicates extract nodeType = Seq.fromList
     . fmap makeError
     . filter ((> 1) . length)
-    . groupSorted getName
+    . NonEmpty.groupAllWith getName
   where
     getName = fst . extract
     makeError directives' = Error
-        { message = makeMessage $ head directives'
-        , locations = snd . extract <$> directives'
+        { message = makeMessage $ NonEmpty.head directives'
+        , locations = snd . extract <$> toList directives'
         }
     makeMessage directive = concat
         [ "There can be only one "