From fdf86b0e155dadc490172f204d559e0858ef4b17 Mon Sep 17 00:00:00 2001
From: Oleg Grenrus <oleg.grenrus@iki.fi>
Date: Thu, 19 Jan 2017 19:05:01 +0200
Subject: [PATCH] Add Semigroup instances

---
 servant-client/servant-client.cabal       |  3 +++
 servant-client/src/Servant/Common/Req.hs  |  7 ++++++-
 servant-docs/servant-docs.cabal           |  4 ++++
 servant-docs/src/Servant/Docs/Internal.hs | 14 +++++++++++---
 4 files changed, 24 insertions(+), 4 deletions(-)

diff --git a/servant-client/servant-client.cabal b/servant-client/servant-client.cabal
index 81069740..97f79174 100644
--- a/servant-client/servant-client.cabal
+++ b/servant-client/servant-client.cabal
@@ -59,6 +59,9 @@ library
     , transformers-base     >= 0.4.4    && < 0.5
     , transformers-compat   >= 0.4      && < 0.6
     , mtl
+  if !impl(ghc >= 8.0)
+    build-depends:
+        semigroups          >=0.16.2.2 && <0.19
   hs-source-dirs: src
   default-language: Haskell2010
   ghc-options: -Wall
diff --git a/servant-client/src/Servant/Common/Req.hs b/servant-client/src/Servant/Common/Req.hs
index 3fb8c5aa..b9dbba0b 100644
--- a/servant-client/src/Servant/Common/Req.hs
+++ b/servant-client/src/Servant/Common/Req.hs
@@ -16,6 +16,7 @@ import Control.Exception
 import Control.Monad
 import Control.Monad.Catch (MonadThrow, MonadCatch)
 import Data.Foldable (toList)
+import Data.Semigroup (Semigroup (..))
 
 import Control.Monad.Error.Class (MonadError(..))
 import Control.Monad.Trans.Except
@@ -27,7 +28,7 @@ import Control.Monad.Reader
 import Control.Monad.Trans.Control (MonadBaseControl (..))
 import Data.ByteString.Lazy hiding (pack, filter, map, null, elem, any)
 import Data.String
-import Data.String.Conversions
+import Data.String.Conversions (cs)
 import Data.Proxy
 import Data.Text (Text)
 import Data.Text.Encoding
@@ -214,6 +215,10 @@ instance MonadBaseControl IO ClientM where
   -- restoreM :: StM ClientM a -> ClientM a
   restoreM st = ClientM (restoreM st)
 
+-- | Try clients in order, last error is preserved.
+instance Semigroup (ClientM a) where
+  a <> b = a `catchError` \_ -> b
+
 runClientM :: ClientM a -> ClientEnv -> IO (Either ServantError a)
 runClientM cm env = runExceptT $ (flip runReaderT env) $ runClientM' cm
 
diff --git a/servant-docs/servant-docs.cabal b/servant-docs/servant-docs.cabal
index 5981fbe9..719ea038 100644
--- a/servant-docs/servant-docs.cabal
+++ b/servant-docs/servant-docs.cabal
@@ -33,6 +33,7 @@ library
     , Servant.Docs.Internal.Pretty
   build-depends:
       base >=4.7 && <5
+    , base-compat >= 0.9.1 && <0.10
     , aeson
     , aeson-pretty
     , bytestring
@@ -46,6 +47,9 @@ library
     , text
     , unordered-containers
     , control-monad-omega == 0.3.*
+  if !impl(ghc >= 8.0)
+    build-depends:
+      semigroups          >=0.16.2.2 && <0.19
   hs-source-dirs: src
   default-language: Haskell2010
   ghc-options: -Wall
diff --git a/servant-docs/src/Servant/Docs/Internal.hs b/servant-docs/src/Servant/Docs/Internal.hs
index 502c540f..2884473c 100644
--- a/servant-docs/src/Servant/Docs/Internal.hs
+++ b/servant-docs/src/Servant/Docs/Internal.hs
@@ -20,6 +20,8 @@
 #include "overlapping-compat.h"
 module Servant.Docs.Internal where
 
+import           Prelude ()
+import           Prelude.Compat
 import           Control.Applicative
 import           Control.Arrow              (second)
 import           Control.Lens               (makeLenses, mapped, over, traversed, view, (%~),
@@ -30,9 +32,10 @@ import qualified Data.ByteString.Char8      as BSC
 import qualified Data.CaseInsensitive       as CI
 import           Data.Hashable              (Hashable)
 import           Data.HashMap.Strict        (HashMap)
-import           Data.List
+import           Data.List.Compat           (intercalate, intersperse, sort)
 import           Data.Maybe
-import           Data.Monoid
+import           Data.Monoid                (All (..), Any (..), Sum (..), Product (..), First (..), Last (..), Dual (..))
+import           Data.Semigroup             (Semigroup (..))
 import           Data.Ord                   (comparing)
 import           Data.Proxy                 (Proxy(Proxy))
 import           Data.String.Conversions    (cs)
@@ -102,8 +105,11 @@ data API = API
   , _apiEndpoints :: HashMap Endpoint Action
   } deriving (Eq, Show)
 
+instance Semigroup API where
+    (<>) = mappend
+
 instance Monoid API where
-    API a1 b1 `mappend` API a2 b2 = API (a1 <> a2) (b1 <> b2)
+    API a1 b1 `mappend` API a2 b2 = API (a1 `mappend` a2) (b1 `mappend` b2)
     mempty = API mempty mempty
 
 -- | An empty 'API'
@@ -162,6 +168,8 @@ data DocNote = DocNote
 -- These are intended to be built using extraInfo.
 -- Multiple ExtraInfo may be combined with the monoid instance.
 newtype ExtraInfo api = ExtraInfo (HashMap Endpoint Action)
+instance Semigroup (ExtraInfo a) where
+    (<>) = mappend
 instance Monoid (ExtraInfo a) where
     mempty = ExtraInfo mempty
     ExtraInfo a `mappend` ExtraInfo b =