Add instances for Float and Double

CHANGELOG.md

@@ -8,7 +8,8 @@ and this project adheres to
 
 ## [Unreleased]
 ### Added
-- `ToGraphQL` and `FromGraphQL` instances for `Word`.
+- `ToGraphQL` and `FromGraphQL` instances for `Word` types, `Float` and
+  `Double`.
 - `Resolver`: Export `ServerException`.
 - `Resolver.defaultResolver`: Throw `FieldNotResolvedException` if the requested
   field is not in the parent object.

src/Language/GraphQL/Class.hs

@@ -79,6 +79,12 @@ instance ToGraphQL a => ToGraphQL (Maybe a) where
 instance ToGraphQL Bool where
     toGraphQL = Type.Boolean
 
+instance ToGraphQL Float where
+    toGraphQL = Type.Float . realToFrac
+
+instance ToGraphQL Double where
+    toGraphQL = Type.Float
+
 -- | Instances of this typeclass can be used to convert GraphQL internal
 -- representation to user-defined type.
 class FromGraphQL a where
@@ -134,3 +140,11 @@ instance FromGraphQL a => FromGraphQL (Maybe a) where
 instance FromGraphQL Bool where
     fromGraphQL (Type.Boolean value) = Just value
     fromGraphQL _ = Nothing
+
+instance FromGraphQL Float where
+    fromGraphQL (Type.Float value) = Just $ realToFrac value
+    fromGraphQL _ = Nothing
+
+instance FromGraphQL Double where
+    fromGraphQL (Type.Float value) = Just value
+    fromGraphQL _ = Nothing