Use deepseq

silently.cabal

@@ -25,7 +25,10 @@ source-repository head
   location: https://github.com/trystan/silently
 
 Library
-  build-depends: base >=4 && <=5, directory -any
+  build-depends:
+      base >=4 && <=5
+    , directory
+    , deepseq
   exposed-modules: System.IO.Silently
   exposed: True
   buildable: True
@@ -66,3 +69,4 @@ test-suite spec
       base
     , hspec-shouldbe
     , directory
+    , deepseq

src/System/IO/Silently.hs

@@ -10,6 +10,7 @@ module System.IO.Silently (
 import GHC.IO.Handle (hDuplicate, hDuplicateTo)
 import System.IO
 import Control.Exception (bracket)
+import Control.DeepSeq
 import System.Directory (removeFile,getTemporaryDirectory)
 
 nullDevice :: FilePath
@@ -66,13 +67,9 @@ hCapture handles action = do
               mapM_ hFlush handles
               hClose tmpHandle
               str <- readFile tmpFile
-              forceList str
-              return (str,a)
+              str `deepseq` return (str,a)
       go hs = goBracket go tmpHandle hs
 
-forceList [] = return ()
-forceList (x:xs) = forceList xs
-
 goBracket :: ([Handle] -> IO a) -> Handle -> [Handle] -> IO a
 goBracket go tmpHandle (h:hs) = bracket (do old <- hDuplicate h
                                             hDuplicateTo tmpHandle h