From a8184a2ee0c9987e618141c0c52f9110b927ea0b Mon Sep 17 00:00:00 2001
From: Nathan van Doorn <nvd1234@gmail.com>
Date: Sat, 13 Jun 2020 15:10:07 +0100
Subject: [PATCH 1/3] Add KnownStatus typeclass

---
 servant/servant.cabal             |   1 +
 servant/src/Servant/API/Status.hs | 153 ++++++++++++++++++++++++++++++
 2 files changed, 154 insertions(+)
 create mode 100644 servant/src/Servant/API/Status.hs

diff --git a/servant/servant.cabal b/servant/servant.cabal
index 2d42c310..bf540e25 100644
--- a/servant/servant.cabal
+++ b/servant/servant.cabal
@@ -55,6 +55,7 @@ library
     Servant.API.RemoteHost
     Servant.API.ReqBody
     Servant.API.ResponseHeaders
+    Servant.API.Status
     Servant.API.Stream
     Servant.API.Sub
     Servant.API.TypeLevel
diff --git a/servant/src/Servant/API/Status.hs b/servant/src/Servant/API/Status.hs
new file mode 100644
index 00000000..8f80938d
--- /dev/null
+++ b/servant/src/Servant/API/Status.hs
@@ -0,0 +1,153 @@
+{-# LANGUAGE DataKinds #-}
+module Servant.API.Status where
+
+import Network.HTTP.Types.Status
+import GHC.TypeNats
+
+-- | Witness that a type-level natural number corresponds to a HTTP status code
+class KnownNat n => KnownStatus n where
+  statusVal :: proxy n -> Status
+
+instance KnownStatus 100 where
+  statusVal _ = status100
+
+instance KnownStatus 101 where
+  statusVal _ = status101
+
+instance KnownStatus 200 where
+  statusVal _ = status200
+
+instance KnownStatus 201 where
+  statusVal _ = status201
+
+instance KnownStatus 202 where
+  statusVal _ = status202
+
+instance KnownStatus 203 where
+  statusVal _ = status203
+
+instance KnownStatus 204 where
+  statusVal _ = status204
+
+instance KnownStatus 205 where
+  statusVal _ = status205
+
+instance KnownStatus 206 where
+  statusVal _ = status206
+
+instance KnownStatus 300 where
+  statusVal _ = status300
+
+instance KnownStatus 301 where
+  statusVal _ = status301
+
+instance KnownStatus 302 where
+  statusVal _ = status302
+
+instance KnownStatus 303 where
+  statusVal _ = status303
+
+instance KnownStatus 304 where
+  statusVal _ = status304
+
+instance KnownStatus 305 where
+  statusVal _ = status305
+
+instance KnownStatus 307 where
+  statusVal _ = status307
+
+instance KnownStatus 308 where
+  statusVal _ = status308
+
+instance KnownStatus 400 where
+  statusVal _ = status400
+
+instance KnownStatus 401 where
+  statusVal _ = status401
+
+instance KnownStatus 402 where
+  statusVal _ = status402
+
+instance KnownStatus 403 where
+  statusVal _ = status403
+
+instance KnownStatus 404 where
+  statusVal _ = status404
+
+instance KnownStatus 405 where
+  statusVal _ = status405
+
+instance KnownStatus 406 where
+  statusVal _ = status406
+
+instance KnownStatus 407 where
+  statusVal _ = status407
+
+instance KnownStatus 408 where
+  statusVal _ = status408
+
+instance KnownStatus 409 where
+  statusVal _ = status409
+
+instance KnownStatus 410 where
+  statusVal _ = status410
+
+instance KnownStatus 411 where
+  statusVal _ = status411
+
+instance KnownStatus 412 where
+  statusVal _ = status412
+
+instance KnownStatus 413 where
+  statusVal _ = status413
+
+instance KnownStatus 414 where
+  statusVal _ = status414
+
+instance KnownStatus 415 where
+  statusVal _ = status415
+
+instance KnownStatus 416 where
+  statusVal _ = status416
+
+instance KnownStatus 417 where
+  statusVal _ = status417
+
+instance KnownStatus 418 where
+  statusVal _ = status418
+
+instance KnownStatus 422 where
+  statusVal _ = status422
+
+instance KnownStatus 426 where
+  statusVal _ = status426
+
+instance KnownStatus 428 where
+  statusVal _ = status428
+
+instance KnownStatus 429 where
+  statusVal _ = status429
+
+instance KnownStatus 431 where
+  statusVal _ = status431
+
+instance KnownStatus 500 where
+  statusVal _ = status500
+
+instance KnownStatus 501 where
+  statusVal _ = status501
+
+instance KnownStatus 502 where
+  statusVal _ = status502
+
+instance KnownStatus 503 where
+  statusVal _ = status503
+
+instance KnownStatus 504 where
+  statusVal _ = status504
+
+instance KnownStatus 505 where
+  statusVal _ = status505
+
+instance KnownStatus 511 where
+  statusVal _ = status511

From 6889d053c7139a08c57a4fb1b4888fec17c6f1ed Mon Sep 17 00:00:00 2001
From: Nathan van Doorn <nvd1234@gmail.com>
Date: Sat, 13 Jun 2020 15:38:36 +0100
Subject: [PATCH 2/3] Add FlexibleInstances for earlier GHCs

---
 servant/src/Servant/API/Status.hs | 2 ++
 1 file changed, 2 insertions(+)

diff --git a/servant/src/Servant/API/Status.hs b/servant/src/Servant/API/Status.hs
index 8f80938d..17a60766 100644
--- a/servant/src/Servant/API/Status.hs
+++ b/servant/src/Servant/API/Status.hs
@@ -1,4 +1,6 @@
 {-# LANGUAGE DataKinds #-}
+-- Flexible instances is necessary on GHC 8.4 and earlier
+{-# LANGUAGE FlexibleInstances #-}
 module Servant.API.Status where
 
 import Network.HTTP.Types.Status

From ff9da1cde499d41fe20fcf167b8c3cee87278979 Mon Sep 17 00:00:00 2001
From: Nathan van Doorn <nvd1234@gmail.com>
Date: Sat, 13 Jun 2020 15:50:12 +0100
Subject: [PATCH 3/3] Use GHC.TypeLits rather than TypeNats

---
 servant/src/Servant/API/Status.hs | 2 +-
 1 file changed, 1 insertion(+), 1 deletion(-)

diff --git a/servant/src/Servant/API/Status.hs b/servant/src/Servant/API/Status.hs
index 17a60766..ee334fcd 100644
--- a/servant/src/Servant/API/Status.hs
+++ b/servant/src/Servant/API/Status.hs
@@ -4,7 +4,7 @@
 module Servant.API.Status where
 
 import Network.HTTP.Types.Status
-import GHC.TypeNats
+import GHC.TypeLits
 
 -- | Witness that a type-level natural number corresponds to a HTTP status code
 class KnownNat n => KnownStatus n where