Return a 404 when we can't find a matching user

bradparker · bradparker · commit 2521f341f511 · 2019-10-02T20:49:47.000+10:00
diff --git a/how-does-servants-type-dsl-work.cabal b/how-does-servants-type-dsl-work.cabal
@@ -10,6 +10,7 @@ executable server
   main-is:             Main.hs
   build-depends:       base ^>=4.12.0.0
                      , aeson
+                     , mtl
                      , servant-server
                      , time
                      , wai
diff --git a/src/Main.hs b/src/Main.hs
@@ -6,6 +6,9 @@
 
 module Main where
 
+import Control.Monad.Error.Class
+  ( throwError
+  )
 import Data.Aeson (ToJSON)
 import Data.Foldable (find)
 import Data.Proxy (Proxy(Proxy))
@@ -21,6 +24,7 @@ import Servant
   , Handler
   , JSON
   , Server
+  , err404
   , serve
   )
 
@@ -72,7 +76,7 @@ matchesUsername uname = (uname ==) . username
 usersShow :: String -> Handler User
 usersShow uname =
   case find (matchesUsername uname) users of
-    Nothing   -> _
+    Nothing   -> throwError err404
     Just user -> pure user
 
 usersServer :: Server UsersAPI
