1 files changed, 26 insertions, 0 deletions
diff --git a/libraries/base/tests/T19719.hs b/libraries/base/tests/T19719.hs
new file mode 100644
index 0000000000..613f92ad6c
--- /dev/null
+++ b/libraries/base/tests/T19719.hs
@@ -0,0 +1,26 @@
+module Main (main) where
+
+import Data.Complex (Complex(..))
+import Data.Functor.Classes (readPrec1, showsPrec1)
+import Text.ParserCombinators.ReadPrec (readPrec_to_S)
+import Text.Read (Read(..))
+
+comp :: Complex Int
+comp = 1 :+ 1
+
+compareInstances :: Int -> IO ()
+compareInstances p = do
+  let precBanner = " (at precedence " ++ show p ++ ")"
+  putStrLn $ "Read vs. Read1" ++ precBanner
+  print (readPrec_to_S readPrec  p "1 :+ 1" :: [(Complex Int, String)])
+  print (readPrec_to_S readPrec1 p "1 :+ 1" :: [(Complex Int, String)])
+  putStrLn ""
+  putStrLn $ "Show vs. Show1" ++ precBanner
+  putStrLn $ showsPrec  p comp ""
+  putStrLn $ showsPrec1 p comp ""
+  putStrLn ""
+
+main :: IO ()
+main = do
+  compareInstances 6
+  compareInstances 7