[Working on ch20
John Goerzen <jgoerzen@complete.org>**20071017173425] {
hunk ./en/ch20-systems.xml 22
-    We will alert you to OS-specific code where it occurs.  Most of the
-    example sessions with &ghci; in this chapter require Linux, MacOS X, or
-    the Cygwin environment for Windows.
+    However, we will be focusing on the POSIX environment for much of the
+    chapter.  POSIX is a standard for Unix-like operating systems such as
+    Linux, FreeBSD, MacOS X, or Solaris.  Windows does not support POSIX by
+    default, but the Cygwin environment provides a POSIX compatibility layer
+    for Windows.
hunk ./en/ch20-systems.xml 55
+  <sect1 id="hs.systems.directories">
+    <title>Directory and File Information</title>
+    <para>
+      The <literal>System.Directory</literal> module contains quite a few
+      functions that can be used to obtain information from the filesystem.
+      You can get a list of files in a directory, rename or delete files,
+      copy files, change the current working directory, or create new
+      directories.  <literal>System.Directory</literal> is portable and works
+      on any platform where GHC itself works.
+    </para>
+    <para>
+      The <ulink
+        url="http://www.haskell.org/ghc/docs/latest/html/libraries/base/System-Directory.html">library
+        reference for <literal>System.Directory</literal></ulink> provides a
+      comprehensive list of the functions available.  Let's use &ghci; to
+      demonstrate a few of them.  Most of these functions are straightforward
+      equivolents to C library calls or shell commands.
+    </para>
+    &dir.ghci:setdir;
+    <para>
+      Here we saw commands to change the current working directory and obtain
+      the current working directory from the system.  These are similar to
+      the <literal>cd</literal> and <literal>pwd</literal> commands in the
+      POSIX shell.
+    </para>
+    &dir.ghci:contents;
+    <para>
+      <literal>getDirectoryContents</literal> returns a list for every item
+      in a given directory.  Note that on POSIX systems, this list normally
+      includes the special values <literal>"."</literal> and
+      <literal>".."</literal>.  You will usually want to filter these out
+      when processing the content of the directory, perhaps like this:
+    </para>
+    &dir.ghci:contents2;
+    <para>
+      You can also query the system about the location of certain
+      directories.   This query will ask the underlying operating system for
+      the information.
+    </para>
+    &dir.ghci:query;
+  </sect1>
+
+  <sect1 id="hs.system.termination">
+    <title>Program Termination</title>
+    <para>
+      Developers often write individual programs to accomplish particular
+      tasks.  These individual parts may be combined to accomplish larger
+      tasks.  A shell script or another program may execute them.  The
+      calling script often needs a way to discover whether the program was
+      able to complete its task successfully.  Haskell automatically
+      indicates a non-successful exit whenever a program is aborted by an
+      exception.
+    </para>
+    <para>However, you may need more fine-grained control over the
+      exit code than that.   Perhaps you need to return different codes for
+      different types of errors.
+      The <literal>System.Exit</literal> module provides a way to exit the
+      program and return a specific exit status code to the caller.  You can
+      call <literal>exitWith ExitSuccess</literal> to return a code
+      indicating a successful termination (0 on POSIX systems).  Or, you can
+      call something like <literal>exitWith (ExitFailure 5)</literal>, which
+      will return code 5 to the calling program.
+    </para>
+  </sect1>
+
+  <sect1 id="hs.systems.datetime">
+    <title>Dates and Times</title>
+    <para>
+      asdf
+    </para>
+  </sect1>
+
+
hunk ./en/ch20-systems.xml 136
-      file.  Here's an example session with the POSIX<footnote><para>POSIX is
-          a standard for Unix-like operating systems.  Linux, FreeBSD,
-          Solaris, and MacOS X are all examples of operating systems that
-          present a POSIX shell and many POSIX-like features.  Windows
-          doesn't, but the Cygwin package can provide many POSIX features for
-          Windows.</para></footnote>
+      file.  Here's an example session with the POSIX
}