As merlyn points out you can not check for this in the same way you can with say C. The reason is simple - although some_non_existing_function() may not exist at compile time, because you can generate functions dynamically in perl *it may well exist by the time it is called*. Consider for example AUTOLOAD which is typically used to dynamically generate non existent accessor functions on demand.

I have always vaguely felt there should be a use strict 'functions' pragma.