+-- | If the function is applied to an absolute path then it returns a
+-- local path obtained by dropping the absolute prefix from the path.
+-- Under Windows the prefix is @\"\\\"@, @\"c:\"@ or @\"c:\\\"@.
+-- Under Unix the prefix is always @\"\/\"@.
+dropAbsolutePrefix :: FilePath -> FilePath
+dropAbsolutePrefix (c:cs) | isPathSeparator c = cs
+#ifdef mingw32_TARGET_OS
+dropAbsolutePrefix (_:':':c:cs) | isPathSeparator c = cs -- path with drive letter
+dropAbsolutePrefix (_:':':cs) = cs
+#endif
+dropAbsolutePrefix cs = cs
+