1 files changed, 34 insertions, 0 deletions
diff --git a/src/Flameshot/Internal/Process.hs b/src/Flameshot/Internal/Process.hs
index 47220a3..e38a145 100644
--- a/src/Flameshot/Internal/Process.hs
+++ b/src/Flameshot/Internal/Process.hs
@@ -36,6 +36,40 @@ data Callbacks = Callbacks
     , onStart :: Pid -> IO ()
     }
 
+instance Semigroup Callbacks where
+  a <> b =
+      Callbacks
+        { onOutLine = \pid s -> do
+          onOutLine a pid s
+          onOutLine b pid s
+
+        , onErrLine = \pid s -> do
+          onErrLine a pid s
+          onErrLine b pid s
+
+        , onError = \pid err -> do
+          onError a pid err
+          onError b pid err
+
+        , onExit = \pid status -> do
+          onExit a pid status
+          onExit b pid status
+
+        , onStart = \pid -> do
+          onStart a pid
+          onStart b pid
+        }
+
+instance Monoid Callbacks where
+  mempty =
+    Callbacks
+      { onOutLine = \_pid _s -> return ()
+      , onErrLine = \_pid _s -> return ()
+      , onError = \_pid _err -> return ()
+      , onExit = \_pid _status -> return ()
+      , onStart = \_pid -> return ()
+      }
+
 run :: FilePath
      -> [String]
      -> Maybe FilePath