Use stderr for errors

kore/app/exec/Main.hs

@@ -34,7 +34,7 @@ import qualified Data.Text as Text
     , split
     )
 import qualified Data.Text.IO as Text
-    ( putStrLn
+    ( hPutStrLn
     , readFile
     )
 import qualified GHC.Generics as GHC
@@ -80,6 +80,7 @@ import System.FilePath
     )
 import System.IO
     ( IOMode (WriteMode)
+    , stderr
     , withFile
     )
 
@@ -804,7 +805,7 @@ koreMerge execOptions mergeOptions = do
             Nothing -> mergeAllRules mainModule ruleIds
     case eitherMergedRule of
         (Left err) -> do
-            lift $ Text.putStrLn err
+            lift $ Text.hPutStrLn stderr err
             return (ExitFailure 1)
         (Right mergedRule) -> do
             let mergedRule' =

kore/app/repl/Main.hs

@@ -63,6 +63,10 @@ import System.Clock
     )
 
 import GlobalMain
+import System.IO
+    ( hPutStrLn
+    , stderr
+    )
 
 -- | Represents a file name along with its module name passed.
 data KoreModule = KoreModule
@@ -213,7 +217,7 @@ mainWithOptions
                     && isNothing (unReplScript replScript)
                     )
                     $ lift $ do
-                        putStrLn
+                        hPutStrLn stderr
                             "You must supply the path to the repl script\
                             \ in order to run the repl in run-script mode."
                         exitFailure
@@ -223,7 +227,7 @@ mainWithOptions
                     && scriptModeOutput == EnableOutput
                     )
                     $ lift $ do
-                        putStrLn
+                        hPutStrLn stderr
                             "The --save-run-output flag is only available\
                             \ when running the repl in run-script mode."
                         exitFailure

kore/src/Kore/BugReport.hs

@@ -146,7 +146,7 @@ withBugReport exeName bugReportOption act =
                     optionalWriteBugReport tmpDir
               | Just (ioe :: IOException) <- fromException someException
               , NoSuchThing <- ioe_type ioe -> do
-                    putStrLn $ displayException someException
+                    hPutStrLn stderr $ displayException someException
                     optionalWriteBugReport tmpDir
               | otherwise -> do
                     let message = displayException someException

kore/src/Kore/Repl.hs

@@ -54,6 +54,8 @@ import Kore.Attribute.RuleIndex
 import qualified Kore.Attribute.RuleIndex as Attribute
 import System.IO
     ( hFlush
+    , hPutStrLn
+    , stderr
     , stdout
     )
 import Text.Megaparsec
@@ -274,7 +276,7 @@ runRepl
     catchInterruptWithDefault a =
         Exception.handle $ \case
             UserInterrupt -> do
-                liftIO $ putStrLn "Step evaluation interrupted."
+                liftIO $ hPutStrLn stderr "Step evaluation interrupted."
                 pure a
             e -> Exception.throwM e
 

kore/src/Kore/Repl/Interpreter.hs

@@ -132,6 +132,8 @@ import System.FilePath
     )
 import System.IO
     ( IOMode (..)
+    , hPutStrLn
+    , stderr
     , withFile
     )
 import System.Process
@@ -1191,7 +1193,7 @@ pipe cmd file args = do
         outputFunc str
         case maybeOutput of
             Nothing ->
-                putStrLn "Error: couldn't access output handle."
+                hPutStrLn stderr "Error: couldn't access output handle."
             Just handle -> do
                 output <- liftIO $ hGetContents handle
                 modifyIORef pipeOut (appReplOut . AuxOut $ output)
@@ -1517,11 +1519,11 @@ parseEvalScript file scriptModeOutput = do
             contents <- lift . liftIO $ readFile file
             let result = runParser scriptParser file (Text.pack contents)
             either parseFailed executeScript result
-        else lift . liftIO . putStrLn $ "Cannot find " <> file
+        else lift . liftIO . hPutStrLn stderr $ "Cannot find " <> file
 
   where
     parseFailed err =
-        lift . liftIO . putStrLn
+        lift . liftIO . hPutStrLn stderr
             $ "\nCouldn't parse repl script file."
             <> "\nParser error at: "
             <> (err & toReplScriptParseErrors & errorBundlePretty)
@@ -1619,4 +1621,4 @@ withExistingDirectory path action =
     ifM
         (doesParentDirectoryExist path)
         (action path)
-        $ liftIO . putStrLn $ "Directory does not exist."
+        $ liftIO . hPutStrLn stderr $ "Directory does not exist."