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Diffstat (limited to 'docs/users_guide/win32-dlls.rst')
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diff --git a/docs/users_guide/win32-dlls.rst b/docs/users_guide/win32-dlls.rst index 26c3ffe3b0..4ecdd10f72 100644 --- a/docs/users_guide/win32-dlls.rst +++ b/docs/users_guide/win32-dlls.rst @@ -97,6 +97,52 @@ Windows. ``IOExts.hSetBinaryMode``. The ``IOExts`` module is part of the ``lang`` package. +.. _windows-file-paths: + +File paths under Windows +------------------------ + +Windows paths are not all the same. The different kinds of paths each have +different meanings. The ``MAX_PATH`` limitation is not a limitation of the operating +system nor the file system. It is a limitation of the default namespace enforced +by the Win32 API for backwards compatibility. + +The NT kernel however allows you ways to opt out of this path preprocessing by +the Win32 APIs. This is done by explicitly using the desired namespace in the +path. + +The namespaces are: + + - file namespace: ``\\?\`` + - device namespace: ``\\.\`` + - NT namespace: ``\`` + +Each of these turn off path processing completely by the Win32 API and the paths +are passed untouched to the filesystem. + +Paths with a drive letter are *legacy* paths. The drive letters are actually +meaningless to the kernel. Just like Unix operating systems, drive letters are +just a mount point. You can view your mount points by using the :command:`mountvol` +command. + +Since GHC 8.6.1, the Haskell I/O manager automatically promotes paths in the legacy +format to Win32 file namespace. By default the I/O manager will do two things to +your paths: + + - replace ``\`` with ``\\`` + - expand relative paths to absolute paths + +If you want to opt out of all preprocessing just expliticly use namespaces in +your paths. Due to this change, if you need to open raw devices (e.g. COM ports) +you need to use the device namespace explicitly. (e.g. ``\\.\COM1``). GHC and +Haskell programs in general no longer support opening devices in the legacy +format. + +See the +`Windows documentation <https://msdn.microsoft.com/en-us/library/windows/desktop/aa365247.aspx>`_ +for more details. + + .. _ghci-cygwin: Using GHC (and other GHC-compiled executables) with Cygwin |