Cleaned up examples/src/videoio-decolor.hs

basvandijk · basvandijk · commit 4829fecfa1c8 · 2017-06-12T00:50:05.000+02:00
diff --git a/examples/src/videoio-decolor.hs b/examples/src/videoio-decolor.hs
@@ -1,7 +1,8 @@
 {-# language DataKinds #-}
 {-# language FlexibleInstances #-}
 
-import Control.Monad ( unless )
+import Control.Monad ( unless, forM_ )
+import Data.Function ( fix )
 import qualified OpenCV as CV
 import OpenCV.TypeLevel
 import OpenCV.Photo
@@ -11,24 +12,21 @@ import OpenCV.Example
 main :: IO ()
 main = do
     cap <- createCaptureArg
-    CV.withWindow "gray" $ \w1 -> CV.withWindow "boost" $ loop cap w1
-  where
-    loop cap grayWindow boostWindow = do
-      _ok <- CV.videoCaptureGrab cap
-      mbImg <- CV.videoCaptureRetrieve cap
-      case mbImg of
-        Just img -> do
-          -- Assert that the retrieved frame is 2-dimensional.
-          let img' :: CV.Mat ('S ['D, 'D]) ('S 3) ('S Word8)
-              img' = CV.exceptError $ CV.coerceMat img
+    CV.withWindow "gray" $ \grayWindow ->
+      CV.withWindow "boost" $ \boostWindow ->
+        fix $ \continue -> do
+          _ok <- CV.videoCaptureGrab cap
+          mbImg <- CV.videoCaptureRetrieve cap
+          forM_ mbImg $ \img -> do
+            -- Assert that the retrieved frame is 2-dimensional.
+            let img' :: CV.Mat ('S ['D, 'D]) ('S 3) ('S Word8)
+                img' = CV.exceptError $ CV.coerceMat img
 
-          let (grayImg, boostImg) = CV.exceptError $ decolor img'
+                (grayImg, boostImg) = CV.exceptError $ decolor img'
 
-          CV.imshow grayWindow grayImg
-          CV.imshow boostWindow boostImg
+            CV.imshow grayWindow grayImg
+            CV.imshow boostWindow boostImg
 
-          key <- CV.waitKey 20
-          -- Loop unless the escape key is pressed.
-          unless (key == 27) $ loop cap grayWindow boostWindow
-        -- Out of frames, stop looping.
-        Nothing -> pure ()
+            key <- CV.waitKey 20
+            -- Loop unless the escape key is pressed.
+            unless (key == 27) continue
