add new type for struct's call

src/HAL/Doc/Struct.hs

+{-# LANGUAGE OverloadedStrings #-}
+{-# LANGUAGE DeriveGeneric #-}
+{-# LANGUAGE TemplateHaskell #-}
+
+module HAL.Doc.Struct where
+
+import GHC.Generics
+
+import Data.Aeson
+import Data.Default
+import Data.Text (pack, Text)
+import Control.Applicative ((<|>))
+import qualified Control.Lens as L
+
+import Servant.API (ToHttpApiData(..))
+
+data Struct = Struct
+  {
+    _struct_docid :: Int,
+    _struct_label :: Text,
+    _struct_parent_docid :: [Int]
+  } deriving (Show, Generic)
+L.makeLenses ''Struct
+
+instance Default Struct where
+  def = Struct def "" def
+
+instance FromJSON Struct where
+  parseJSON (Object o) = Struct <$>
+    (o .: "docid")
+    <*> (o .: "label_s")
+    <*> (o .: "parentDocid_i" <|> return [])
+
+instance ToHttpApiData Struct where
+  toUrlPiece _ = "docid,label_s,parentDocid_i"