Add QueryParamForm to API

Author: isairz

servant/src/Servant/API.hs

@@ -71,7 +71,7 @@ import           Servant.API.Header          (Header (..))
 import           Servant.API.HttpVersion     (HttpVersion (..))
 import           Servant.API.IsSecure        (IsSecure (..))
 import           Servant.API.QueryParam      (QueryFlag, QueryParam,
-                                              QueryParams)
+                                              QueryParams, QueryParamForm)
 import           Servant.API.Raw             (Raw)
 import           Servant.API.RemoteHost      (RemoteHost)
 import           Servant.API.ReqBody         (ReqBody)

servant/src/Servant/API/QueryParam.hs

@@ -3,7 +3,7 @@
 {-# LANGUAGE TypeOperators      #-}
 {-# LANGUAGE PolyKinds          #-}
 {-# OPTIONS_HADDOCK not-home    #-}
-module Servant.API.QueryParam (QueryFlag, QueryParam, QueryParams) where
+module Servant.API.QueryParam (QueryFlag, QueryParam, QueryParams, QueryParamForm) where
 
 import           Data.Typeable (Typeable)
 import           GHC.TypeLits (Symbol)
@@ -42,6 +42,22 @@ data QueryParams (sym :: Symbol) a
 -- >>> type MyApi = "books" :> QueryFlag "published" :> Get '[JSON] [Book]
 data QueryFlag (sym :: Symbol)
 
+-- | Lookup the values associated to the query string parameter
+-- and try to extract it as a value of type @a@.
+--
+-- Example:
+--
+-- >>> -- /books?title=<title>&authors[]=<author1>&authors[]=<author2>&page=<page>
+-- >>> data BookSearchParams = BookSearchParams
+-- >>>   { title :: Text
+-- >>>   { authors :: [Text]
+-- >>>   , page :: Maybe Int
+-- >>>   } deriving (Generic)
+-- >>> instance FromForm BookSearchParams
+-- >>> type MyApi = "books" :> QueryParamForm BookSearchParams :> Get '[JSON] [Book]
+data QueryParamForm a
+    deriving Typeable
+
 -- $setup
 -- >>> import Servant.API
 -- >>> import Data.Aeson

servant/src/Servant/API/TypeLevel.hs

@@ -51,7 +51,8 @@ import           GHC.Exts                (Constraint)
 import           Servant.API.Alternative (type (:<|>))
 import           Servant.API.Capture     (Capture, CaptureAll)
 import           Servant.API.Header      (Header)
-import           Servant.API.QueryParam  (QueryFlag, QueryParam, QueryParams)
+import           Servant.API.QueryParam  (QueryFlag, QueryParam,
+                                          QueryParams, QueryParamForm)
 import           Servant.API.ReqBody     (ReqBody)
 import           Servant.API.Sub         (type (:>))
 import           Servant.API.Verbs       (Verb)
@@ -123,6 +124,7 @@ type family IsElem endpoint api :: Constraint where
                                           = IsElem sa sb
   IsElem sa (QueryParam x y :> sb)        = IsElem sa sb
   IsElem sa (QueryParams x y :> sb)       = IsElem sa sb
+  IsElem sa (QueryParamForm x :> sb)      = IsElem sa sb
   IsElem sa (QueryFlag x :> sb)           = IsElem sa sb
   IsElem (Verb m s ct typ) (Verb m s ct' typ)
                                           = IsSubList ct ct'