I'm toying in build a new language (more in the "find ideas" than really doing it), and tough: Why I can't have events on functions? ie: Why I can't attach list

I'm toying in build a new language (more in the "find ideas" than really doing it), and tough: Why I can't have events on functions? ie: Why I can't attach listener to the entry/exit of a function, in a transparent way (from https://gist.github.com/3777791 https://gist.github.com/3777791, where is still ugly as hell): def startDef: self.cache['start'] = now def endDef: performance.register(self.function.__name,'time', now - self.cache['start']) hook(sample,pre = startDef, post = endDef) Now with that ability, is possible to log with a graph the flow of the data in the program, in realtime. Still will lack the instant play but is a good start...