@@ -28,6 +28,7 @@ module Servant.API.UVerb
2828 HasStatus (StatusOf),
2929 statusOf,
3030 HasStatuses (Statuses, statuses),
31+ WithStatus (..),
3132 module Servant.API.UVerb.Union,
3233 )
3334where
@@ -35,7 +36,7 @@ where
3536import Data.Proxy (Proxy (Proxy))
3637import GHC.TypeLits (Nat)
3738import Network.HTTP.Types (Status, StdMethod)
38−import Servant.API.ContentTypes (MimeRender (mimeRender), MimeUnrender (mimeUnrender), NoContent)
39+import Servant.API.ContentTypes (NoContent, MimeRender(mimeRender), MimeUnrender(mimeUnrender))
3940import Servant.API.Status (KnownStatus, statusVal)
4041import Servant.API.UVerb.Union
4142
@@ -63,6 +64,36 @@ instance (HasStatus a, HasStatuses as) => HasStatuses (a ': as) where
6364 type Statuses (a ': as) = StatusOf a ': Statuses as
6465 statuses _ = statusOf (Proxy :: Proxy a) : statuses (Proxy :: Proxy as)
6566
67+-- | A simple newtype wrapper that pairs a type with its status code. It
68+-- implements all the content types that Servant ships with by default.
69+newtype WithStatus (k :: Nat) a = WithStatus a
70+ deriving (Eq, Show)
71+
72+instance MimeRender ctype a => MimeRender ctype (WithStatus _status a) where
73+ mimeRender contentTypeProxy (WithStatus a) = mimeRender contentTypeProxy a
74+
75+instance MimeUnrender ctype a => MimeUnrender ctype (WithStatus _status a) where
76+ mimeUnrender contentTypeProxy input =
77+ WithStatus <$> mimeUnrender contentTypeProxy input
78+
79+-- | an instance of this typeclass assigns a HTTP status code to a return type
80+--
81+-- Example:
82+--
83+-- @
84+-- data NotFoundError = NotFoundError String
85+--
86+-- instance HasStatus NotFoundError where
87+-- type StatusOf NotFoundError = 404
88+-- @
89+--
90+-- You can also use the convience newtype wrapper 'WithStatus' if you want to
91+-- avoid writing a 'HasStatus' instance manually. It also has the benefit of
92+-- showing the status code in the type; which might aid in readability.
93+instance KnownStatus n => HasStatus (WithStatus n a) where
94+ type StatusOf (WithStatus n a) = n
95+
96+
6697-- | A variant of 'Verb' that can have any of a number of response values and status codes.
6798--
6899-- FUTUREWORK: it would be nice to make 'Verb' a special case of 'UVerb', and only write