'Returns a string for the function interface.
The routine should have a single result object, which can be None.
If the routine has multiple result objects, a CodeGenError is
raised.
See: http://en.wikipedia.org/wiki/Function_prototype'

def get_interface(self, routine):

    prototype = ['interface\n']
    prototype.extend(self._get_routine_opening(routine))
    prototype.extend(self._declare_arguments(routine))
    prototype.extend(self._get_routine_ending(routine))
    prototype.append('end    interface\n')
    return ''.join(prototype)
