Use osascript to display message on mac

cardano-launcher/app/Main.hs

@@ -10,10 +10,11 @@ import qualified Prelude
 import           Data.IORef (newIORef, readIORef, writeIORef)
 import           Data.Text.Lazy.Builder (fromString, fromText)
 
-import           Distribution.System (OS (Windows), buildOS)
+import           Distribution.System (OS (Windows, OSX), buildOS)
 import           System.Environment (setEnv)
 import           System.Exit (exitWith)
 import           System.IO.Silently (hSilence)
+import           System.Process (waitForProcess, withCreateProcess, proc)
 
 import           Formatting (bprint, build, formatToString)
 import           Formatting.Buildable (Buildable (..))
@@ -40,7 +41,7 @@ import           Cardano.Shell.Launcher (LoggingDependencies (..), TLSError,
                                          walletRunnerProcess)
 import           Cardano.Shell.Update.Lib (UpdaterData (..),
                                            runDefaultUpdateProcess)
-import           Control.Exception.Safe (throwM)
+import           Control.Exception.Safe (throwM, tryAny)
 
 
 --------------------------------------------------------------------------------
@@ -49,7 +50,7 @@ import           Control.Exception.Safe (throwM)
 
 -- | Main function.
 main :: IO ()
-main = silence $ do
+main = showErrorDarwin $ silence $ do
 
     defaultConfigPath   <- getDefaultConfigPath
 
@@ -277,3 +278,27 @@ silence :: IO a -> IO a
 silence runAction = case buildOS of
     Windows -> hSilence [stdout, stderr] runAction
     _       -> runAction
+
+showErrorDarwin :: IO a -> IO a
+showErrorDarwin action = case buildOS of 
+    OSX -> do
+        eVal <- tryAny action
+        case eVal of
+            Left err -> do
+                displayErrorDarwin (show err)
+                throwM err
+            Right val -> return val
+    _ -> action
+  where
+    displayErrorDarwin :: Text -> IO ()
+    displayErrorDarwin errorMessage = do
+        let displayProcess = proc "osascript" ["-e", toS (mkErrorMessage errorMessage)]
+        void $ withCreateProcess displayProcess (\ _ _ _ ph -> waitForProcess ph)
+    mkErrorMessage :: Text -> Text
+    mkErrorMessage errorMessage = mconcat
+          [ "display dialog "
+          , show (errorMessage :: Text)
+          , " buttons {\"Ok\"} "
+          , "default button 1 with title "
+          , show ("Cardano Launcher Error" :: Text)
+          ]

cardano-launcher/cardano-launcher.cabal

@@ -84,6 +84,7 @@ executable cardano-launcher
     , text
     , silently
     , Cabal
+    , process
     -- cli
     , optparse-applicative
 

cardano-launcher/src/Cardano/Shell/Environment.hs

@@ -10,7 +10,7 @@ import           Cardano.Prelude
 import           Cardano.Shell.Template (substituteA)
 import           Data.Yaml (Value (..))
 import           System.Environment (lookupEnv)
-
+import Prelude (Show(..))
 -- | Substitute envrionment variable with value of its name.
 --
 -- @
@@ -33,7 +33,10 @@ expandVariable var = do
 data SubstitutionError
   = FailedToLookupEnv Text
   -- ^ Failed to lookup environment variable
-  deriving (Eq, Show)
+  deriving (Eq)
+
+instance Show SubstitutionError where
+  show (FailedToLookupEnv env) = "Failed to lookup environment variable: " <> toS env
 
 -- | Given an Aeson 'Value', parse and substitute environment variables in all
 -- 'String' objects.