* Help text for all (non-script) programs, so no more:

$ nix-instantiate --help
error: unknown flag `--help`
Try `nix-instantiate --help' for more information.

:-)

src/libmain/shared.hh

@@ -6,8 +6,17 @@
 #include "util.hh"
 
 
+/* These are not implemented here, but must be implemented by a
+   program linking against libmain. */
+
+/* Main program.  Called by main() after the ATerm library has been
+   initialised and some default arguments have been processed (and
+   removed from `args').  main() will catch all exceptions. */
 void run(Strings args);
 
+/* Should print a help message to stdout and return. */
+void printHelp();
+
 
 extern string programId;