[CMake] Macro callbacks

[KSpam]

Is it possible to  call variable macro names from within another macro?  The 
following is a simple (non-working) example of what I would like to do:

	macro (do_something callback)
		# Call the callback macro and pass a message argument
		${callback}("Hello world")
	endmacro (do_something)

	macro (my_callback msg)
		message("${msg}")
	endmacro (my_callback)

	# Call do_something macro, which will call my_callback macro as a callback
	set(callback_name my_callback)
	do_something(${callback_name})

Thanks,
Justin