Handle Output enumerations in Schema definition

The third end-to-end test from graphql-js was implemented.

Data/GraphQL/Execute.hs

@@ -33,6 +33,9 @@ selection _ _ = error "selection: Not implemented yet"
 output :: (Alternative f, Monad f) => SelectionSet -> Output f -> f Aeson.Value
 output sels (OutputResolver resolv) = selectionSet resolv sels
 output sels (OutputList os) = fmap array . traverse (output sels) =<< os
+output sels (OutputEnum e)
+   | null sels = Aeson.toJSON <$> e
+   | otherwise = empty
 output sels (OutputScalar s)
    | null sels = Aeson.toJSON <$> s
    | otherwise = empty

Data/GraphQL/Schema.hs

@@ -14,8 +14,8 @@ type Resolver f = Input -> f (Output f)
 data Output f = OutputResolver (Resolver f)
               | OutputList (f [Output f])
               | OutputScalar (f Scalar)
+              | OutputEnum (f Text)
            -- | OutputUnion [Output]
-           -- | OutputEnum [Scalar]
            -- | OutputNonNull (Output)
 
 data Input = InputScalar Scalar

tests/Test/StarWars.hs

@@ -25,13 +25,14 @@ import Data.GraphQL.Schema
 -- See https://github.com/graphql/graphql-js/blob/master/src/__tests__/starWarsQueryTests.js
 
 test :: TestTree
-test = testGroup "Basic Queries"
+test = testGroup "Star Wars Query Tests"
+  [ testGroup "Basic Queries"
     [ testCase "R2-D2 hero" $ (@?=) (graphql schema [r|
-query HeroNameQuery {
+  query HeroNameQuery {
     hero {
       id
     }
-}|]) . Just
+  }|]) . Just
       $ object [
           "hero" .= object [
                 "id"   .= ("2001" :: Text)
@@ -39,7 +40,7 @@ query HeroNameQuery {
           ]
 
     , testCase "R2-D2 ID and friends" $ (@?=) (graphql schema [r|
-query HeroNameAndFriendsQuery {
+  query HeroNameAndFriendsQuery {
     hero {
       id
       name
@@ -47,7 +48,7 @@ query HeroNameAndFriendsQuery {
         name
       }
     }
-}|]) . Just
+  }|]) . Just
        $ object [
             "hero" .= object [
                 "id" .= ("2001" :: Text)
@@ -60,6 +61,58 @@ query HeroNameAndFriendsQuery {
               ]
        ]
     ]
+  , testGroup "Nested Queries"
+    [ testCase "R2-D2 friends" $ (@?=) (graphql schema [r|
+  query NestedQuery {
+    hero {
+      name
+      friends {
+        name
+        appearsIn
+        friends {
+          name
+        }
+      }
+    }
+  }|]) . Just
+       $ object [
+           "hero" .= object [
+                "name" .= ("R2-D2" :: Text)
+              , "friends" .= [
+                     object [
+                         "name" .= ("Luke Skywalker" :: Text)
+                       , "appearsIn" .= ["NEWHOPE","EMPIRE","JEDI" :: Text]
+                       , "friends" .= [
+                             object ["name" .= ("Han Solo" :: Text)]
+                           , object ["name" .= ("Leia Organa" :: Text)]
+                           , object ["name" .= ("C-3PO" :: Text)]
+                           , object ["name" .= ("R2-D2" :: Text)]
+                           ]
+                       ]
+                   , object [
+                         "name" .= ("Han Solo" :: Text)
+                       , "appearsIn" .= [ "NEWHOPE","EMPIRE","JEDI" :: Text]
+                       , "friends" .= [
+                             object ["name" .= ("Luke Skywalker" :: Text)]
+                           , object ["name" .= ("Leia Organa" :: Text)]
+                           , object ["name" .= ("R2-D2" :: Text)]
+                           ]
+                       ]
+                   , object [
+                         "name" .= ("Leia Organa" :: Text)
+                       , "appearsIn" .= [ "NEWHOPE","EMPIRE","JEDI" :: Text]
+                       , "friends" .= [
+                             object ["name" .= ("Luke Skywalker" :: Text)]
+                           , object ["name" .= ("Han Solo" :: Text)]
+                           , object ["name" .= ("C-3PO" :: Text)]
+                           , object ["name" .= ("R2-D2" :: Text)]
+                           ]
+                       ]
+                   ]
+               ]
+           ]
+      ]
+  ]
 
 -- * Schema
 -- See https://github.com/graphql/graphql-js/blob/master/src/__tests__/starWarsSchema.js
@@ -91,6 +144,12 @@ droid (InputList (InputScalar (ScalarID i) : inputFields)) =
     withFields inputFields <$> getDroid i
 droid _ = empty
 
+episode :: Alternative f => Int -> Output f
+episode 4 = OutputEnum $ pure "NEWHOPE"
+episode 5 = OutputEnum $ pure "EMPIRE"
+episode 6 = OutputEnum $ pure "JEDI"
+episode _ = OutputEnum empty
+
 characterOutput :: Alternative f => Text -> Character -> f (Output f)
 characterOutput "id" char =
     pure $ OutputScalar . pure . ScalarString $ id_  char
@@ -99,6 +158,8 @@ characterOutput "name" char =
 characterOutput "friends" char =
     pure . OutputList . pure $ OutputResolver . (\c (InputField f) ->
       characterOutput f c) <$> getFriends char
+characterOutput "appearsIn" char =
+    pure $ OutputList . pure . fmap episode $ appearsIn char
 characterOutput _ _ = empty
 
 withFields :: Alternative f => [Input] -> Character -> Output f