In particular, this patch fixes a bunch of known and unknown failing tests on MinGW for GHC. For a little background, _isatty on Windows doesn't actually test for a TTY: it just tests for a character device [1]. So it will spuriously report true for NUL. [1] http://msdn.microsoft.com/en-us/library/f4s0ddew(v=VS.80).aspx Excerpts from Edward Z. Yang's message of Tue Sep 07 15:55:40 -0400 2010:

1 patch for repository http://darcs.haskell.org/packages/base:

Tue Sep 7 11:41:44 EDT 2010 Edward Z. Yang * More accurate isatty test for MinGW.