config: added Show instance

servant-server/src/Servant/Server/Internal/Config.hs

@@ -34,14 +34,21 @@ data Config a where
     EmptyConfig :: Config '[]
     ConsConfig :: x -> Config xs -> Config (x ': xs)
 
+instance Show (Config '[]) where
+  show EmptyConfig = "EmptyConfig"
+instance (Show a, Show (Config as)) => Show (Config (ConfigEntry tag a ': as)) where
+  showsPrec outerPrecedence (ConsConfig (ConfigEntry a) as) =
+    showParen (outerPrecedence > 5) $
+      shows a . showString " .: " . shows as
+
 instance Eq (Config '[]) where
     _ == _ = True
-instance (Eq a, Eq (Config as)) => Eq (Config (a ' : as)) where
+instance (Eq a, Eq (Config as)) => Eq (Config (a ': as)) where
     ConsConfig x1 y1 == ConsConfig x2 y2 = x1 == x2 && y1 == y2
 
 (.:) :: x -> Config xs -> Config (ConfigEntry tag x ': xs)
 e .: cfg = ConsConfig (ConfigEntry e) cfg
-infixr 4 .:
+infixr 5 .:
 
 class HasConfigEntry (cfg :: [*]) (a :: k) (val :: *) | cfg a -> val where
     getConfigEntry :: proxy a -> Config cfg -> val

servant-server/test/Servant/Server/Internal/ConfigSpec.hs

@@ -3,9 +3,10 @@
 module Servant.Server.Internal.ConfigSpec (spec) where
 
 import           Data.Proxy                     (Proxy (..))
-import           Test.Hspec                     (Spec, describe, it, shouldBe)
+import           Test.Hspec                     (Spec, describe, it, shouldBe, pending, context)
 import           Test.ShouldNotTypecheck        (shouldNotTypecheck)
 
+import           Servant.API
 import           Servant.Server.Internal.Config
 
 spec :: Spec
@@ -26,6 +27,23 @@ getConfigEntrySpec = describe "getConfigEntry" $ do
 
     getConfigEntry (Proxy :: Proxy "a") cfg2 `shouldBe` 1
 
+  it "allows to distinguish between different config entries with the same type by tag" $ do
+    let cfg = 'a' .: 'b' .: EmptyConfig :: Config '[ConfigEntry 1 Char, ConfigEntry 2 Char]
+    print cfg
+    getConfigEntry (Proxy :: Proxy 1) cfg `shouldBe` 'a'
+
+  context "Show instance" $ do
+    let cfg = 1 .: 2 .: EmptyConfig
+    it "has a Show instance" $ do
+      show cfg `shouldBe` "1 .: 2 .: EmptyConfig"
+
+    it "bracketing works" $ do
+      show (Just cfg) `shouldBe` "Just (1 .: 2 .: EmptyConfig)"
+
+    it "bracketing works with operators" $ do
+      let cfg = (1 .: 'a' .: EmptyConfig) :<|> ('b' .: True .: EmptyConfig)
+      show cfg `shouldBe` "(1 .: 'a' .: EmptyConfig) :<|> ('b' .: True .: EmptyConfig)"
+
   it "does not typecheck if key does not exist" $ do
 
     let x = getConfigEntry (Proxy :: Proxy "b") cfg1 :: Int