3 files changed, 21 insertions, 11 deletions
diff --git a/src/Language/GraphQL/Execute/Execution.hs b/src/Language/GraphQL/Execute/Execution.hs
index fe4ad82..22f3595 100644
--- a/src/Language/GraphQL/Execute/Execution.hs
+++ b/src/Language/GraphQL/Execute/Execution.hs
@@ -107,17 +107,22 @@ executeField :: (Monad m, Serialize a)
     -> Type.Value
     -> NonEmpty (Transform.Field m)
     -> CollectErrsT m a
-executeField (Out.ValueResolver fieldDefinition resolver) prev fields = do
-    let Out.Field _ fieldType argumentDefinitions = fieldDefinition
-    let (Transform.Field _ _ arguments' _ :| []) = fields
-    case coerceArgumentValues argumentDefinitions arguments' of
-        Nothing -> addErrMsg "Argument coercing failed."
-        Just argumentValues -> do
-            answer <- lift $ resolveFieldValue prev argumentValues resolver
-            case answer of
-                Right result -> completeValue fieldType fields result
-                Left errorMessage -> addErrMsg errorMessage
-executeField _ _ _ = addErrMsg "No field value resolver specified."
+executeField fieldResolver prev fields
+    | Out.ValueResolver fieldDefinition resolver <- fieldResolver =
+        executeField' fieldDefinition resolver
+    | Out.EventStreamResolver fieldDefinition resolver _ <- fieldResolver =
+        executeField' fieldDefinition resolver
+  where
+    executeField' fieldDefinition resolver = do
+        let Out.Field _ fieldType argumentDefinitions = fieldDefinition
+        let (Transform.Field _ _ arguments' _ :| []) = fields
+        case coerceArgumentValues argumentDefinitions arguments' of
+            Nothing -> addErrMsg "Argument coercing failed."
+            Just argumentValues -> do
+                answer <- lift $ resolveFieldValue prev argumentValues resolver
+                case answer of
+                    Right result -> completeValue fieldType fields result
+                    Left errorMessage -> addErrMsg errorMessage
 
 completeValue :: (Monad m, Serialize a)
     => Out.Type m
diff --git a/src/Language/GraphQL/Execute/Transform.hs b/src/Language/GraphQL/Execute/Transform.hs
index 086af5c..0c29368 100644
--- a/src/Language/GraphQL/Execute/Transform.hs
+++ b/src/Language/GraphQL/Execute/Transform.hs
@@ -239,6 +239,10 @@ document schema operationName subs ast = do
             | Just mutationType <- mutation schema ->
                 pure $ Document referencedTypes mutationType
                     $ operation chosenOperation replacement
+        OperationDefinition Full.Subscription _ _ _ _
+            | Just subscriptionType <- subscription schema ->
+                pure $ Document referencedTypes subscriptionType
+                    $ operation chosenOperation replacement
         _ -> Left UnsupportedRootOperation
 
 defragment
diff --git a/src/Language/GraphQL/Type/Schema.hs b/src/Language/GraphQL/Type/Schema.hs
index 8cf0383..c5cc6fd 100644
--- a/src/Language/GraphQL/Type/Schema.hs
+++ b/src/Language/GraphQL/Type/Schema.hs
@@ -29,4 +29,5 @@ data Type m
 data Schema m = Schema
     { query :: Out.ObjectType m
     , mutation :: Maybe (Out.ObjectType m)
+    , subscription :: Maybe (Out.ObjectType m)
     }