Add deriveToGraphQL

… for deriving `ToGraphQL` instances automatically.

tests/Language/GraphQL/ClassSpec.hs

@@ -3,6 +3,7 @@
    obtain one at https://mozilla.org/MPL/2.0/. -}
 
 {-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE TemplateHaskell #-}
 module Language.GraphQL.ClassSpec
     ( spec
     ) where
@@ -11,8 +12,16 @@ import Data.Text (Text)
 import Data.Time (UTCTime(..))
 import Data.Time.Calendar.OrdinalDate (fromOrdinalDate)
 import qualified Language.GraphQL.Type as Type
-import Language.GraphQL.Class (FromGraphQL(..), ToGraphQL(..))
+import Language.GraphQL.Class (FromGraphQL(..), ToGraphQL(..), deriveToGraphQL)
 import Test.Hspec (Spec, describe, it, shouldBe)
+import qualified Data.HashMap.Strict as HashMap
+
+data TwoFieldRecord = TwoFieldRecord
+    { x :: Int
+    , y :: Bool
+    }
+
+$(deriveToGraphQL ''TwoFieldRecord)
 
 spec :: Spec
 spec = do
@@ -65,3 +74,16 @@ spec = do
                     }
                 actual = fromGraphQL given
              in actual `shouldBe` expected
+
+    describe "deriveToGraphQL" $ do
+        it "derives ToGraphQL for a record" $ do
+            let expected = Type.Object $ HashMap.fromList
+                    [ ("x", Type.Int 1)
+                    , ("y", Type.Boolean True)
+                    , ("__typename", Type.String "TwoFieldRecord")
+                    ]
+                given = TwoFieldRecord
+                    { x = 1
+                    , y = True
+                    }
+             in toGraphQL given `shouldBe` expected