[GHC] #4452: Graphics.Win32.GDI.Clip.enumClipboardFormats fails on success.

[GHC]

#4452: Graphics.Win32.GDI.Clip.enumClipboardFormats fails on success.
----------------------------------+-----------------------------------------
    Reporter:  fryguybob          |        Owner:                             
        Type:  bug                |       Status:  new                        
    Priority:  normal             |    Milestone:                             
   Component:  libraries (other)  |      Version:  6.12.3                     
    Keywords:  Win32, Clipboard   |     Testcase:                             
   Blockedby:                     |   Difficulty:                             
          Os:  Windows            |     Blocking:                             
Architecture:  Unknown/Multiple   |      Failure:  Incorrect result at runtime
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Description changed by igloo:

Old description:

> According to the documentation for the Win32 EnumClipboardFormats
> function:
>
> http://msdn.microsoft.com/en-us/library/ms649038(VS.85).aspx
>
> A return value of zero is only an error if a subsequent call to
> GetLastError does not return ERROR_SUCCESS.  The following code is what I
> would expect:
>

> {{{
> errorWinNotErrorSuccess :: (Num a) => String -> IO a
> errorWinNotErrorSuccess fn_name = do
>   err_code <- getLastError
>   if err_code == 0 then return 0 else failWith fn_name err_code
>
> failIfZeroAndNotErrorSuccess :: Num a => String -> IO a -> IO a
> failIfZeroAndNotErrorSuccess wh act = do
>   v <- act
>   if v == 0 then errorWinNotErrorSuccess wh else return v
>
> enumClipboardFormats :: ClipboardFormat -> IO ClipboardFormat
> enumClipboardFormats format =
>   failIfZeroAndNotErrorSuccess "EnumClipboardFormats" $
> c_EnumClipboardFormats format
> }}}
>
> Instead of the current:
>
> {{{
> enumClipboardFormats :: ClipboardFormat -> IO ClipboardFormat
> enumClipboardFormats format =
>   failIfZero "EnumClipboardFormats" $ c_EnumClipboardFormats format
> }}}

New description:

 According to the documentation for the Win32 !EnumClipboardFormats
 function:

 http://msdn.microsoft.com/en-us/library/ms649038(VS.85).aspx

 A return value of zero is only an error if a subsequent call to
 !GetLastError does not return ERROR_SUCCESS.  The following code is what I
 would expect:


 {{{
 errorWinNotErrorSuccess :: (Num a) => String -> IO a
 errorWinNotErrorSuccess fn_name = do
   err_code <- getLastError
   if err_code == 0 then return 0 else failWith fn_name err_code

 failIfZeroAndNotErrorSuccess :: Num a => String -> IO a -> IO a
 failIfZeroAndNotErrorSuccess wh act = do
   v <- act
   if v == 0 then errorWinNotErrorSuccess wh else return v

 enumClipboardFormats :: ClipboardFormat -> IO ClipboardFormat
 enumClipboardFormats format =
   failIfZeroAndNotErrorSuccess "EnumClipboardFormats" $
 c_EnumClipboardFormats format
 }}}

 Instead of the current:

 {{{
 enumClipboardFormats :: ClipboardFormat -> IO ClipboardFormat
 enumClipboardFormats format =
   failIfZero "EnumClipboardFormats" $ c_EnumClipboardFormats format
 }}}

--

-- 
Ticket URL: <http://hackage.haskell.org/trac/ghc/ticket/4452#comment:1>
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