Avoid non-exhaustive pattern match.

1 files changed, 12 insertions, 10 deletions

diff --git a/src/Text/Pandoc/ImageSize.hs b/src/Text/Pandoc/ImageSize.hs
index c5fe98a66..00ab86eab 100644
--- a/src/Text/Pandoc/ImageSize.hs
+++ b/src/Text/Pandoc/ImageSize.hs
@@ -319,20 +319,22 @@ pngSize img = do
                     (shift w1 24 + shift w2 16 + shift w3 8 + w4,
                      shift h1 24 + shift h2 16 + shift h3 8 + h4)
                 _ -> Nothing -- "PNG parse error"
-  let (dpix, dpiy) = findpHYs rest''
+  (dpix, dpiy) <- findpHYs rest''
   return ImageSize { pxX  = x, pxY = y, dpiX = dpix, dpiY = dpiy }
 
-findpHYs :: ByteString -> (Integer, Integer)
+findpHYs :: ByteString -> Maybe (Integer, Integer)
 findpHYs x
-  | B.null x || "IDAT" `B.isPrefixOf` x = (72,72)
+  | B.null x || "IDAT" `B.isPrefixOf` x = return (72,72)
   | "pHYs" `B.isPrefixOf` x =
-    let [x1,x2,x3,x4,y1,y2,y3,y4,u] =
-          map fromIntegral $ unpack $ B.take 9 $ B.drop 4 x
-        factor = if u == 1 -- dots per meter
-                    then \z -> z * 254 `div` 10000
-                    else const 72
-    in  ( factor $ shift x1 24 + shift x2 16 + shift x3 8 + x4,
-          factor $ shift y1 24 + shift y2 16 + shift y3 8 + y4 )
+    case map fromIntegral $ unpack $ B.take 9 $ B.drop 4 x of
+         [x1,x2,x3,x4,y1,y2,y3,y4,u] -> do
+           let factor = if u == 1 -- dots per meter
+                          then \z -> z * 254 `div` 10000
+                          else const 72
+           return
+              ( factor $ shift x1 24 + shift x2 16 + shift x3 8 + x4,
+                factor $ shift y1 24 + shift y2 16 + shift y3 8 + y4 )
+         _ -> mzero
   | otherwise = findpHYs $ B.drop 1 x  -- read another byte
 
 gifSize :: ByteString -> Maybe ImageSize