use default challenges if file does not exist

1 files changed, 10 insertions, 4 deletions

diff --git a/lambda-calcul/haskell/src/Minilang/Server.hs b/lambda-calcul/haskell/src/Minilang/Server.hs
index ea66e1e..7cf5718 100644
--- a/lambda-calcul/haskell/src/Minilang/Server.hs
+++ b/lambda-calcul/haskell/src/Minilang/Server.hs
@@ -13,7 +13,7 @@ import Data.Aeson
     decode,
     eitherDecodeFileStrict,
     object,
-    (.=),
+    (.=), eitherDecode,
   )
 import Data.ByteString.Lazy (fromStrict)
 import Data.Data (Proxy (..))
@@ -31,6 +31,8 @@ import Servant (hoistServer)
 import Servant.Server (serve)
 import System.Log.FastLogger (fromLogStr)
 import System.Random (newStdGen)
+import Control.Exception (try)
+import qualified Data.ByteString.Lazy as LBS
 
 data Server = Server
   { -- | If the server is running, this will contain the underlying
@@ -71,9 +73,13 @@ startServer serverPort = do
 
 readChallenges :: IO [Challenge]
 readChallenges = do
-  eitherDecodeFileStrict "challenges.json" >>= \case
-    Right challenges -> pure challenges
-    Left _ -> pure defaultChallenges
+  file <- try $ LBS.readFile "challenges.json"
+  case file of
+    Left (_ :: IOError) -> pure defaultChallenges
+    Right content -> case eitherDecode content of
+      Right challenges -> pure challenges
+      Left _ -> pure defaultChallenges
+
 
 serveAPI :: Env -> Application
 serveAPI env =