Is it possible to have patch where an [expr~ ] object output can modify the [expr~ ] object itself at the level of code functionality ?. Because i am thinking about this idea if it is possible in Pure Data to have objects that can self-modify some parts of other objects or the same objects that started the process ? Thank you very much.

Robert.

@Boran Robert I do not think that is possible, you can only replace variables. you could create expressions with dynamic patching, but i am not sure if that would be worth the work.
but, you can do iteration with expr. for audio signals you need one block delay, like in this patch:
iterateexpr~.pd
and this is an idea for syncing audio and control rate data, it works on the audio block level:
controlsignalsync.pd possibly the audio frequencies sample size needs also to be n*blocksize for working nicely with the synced control data... interestingly i could use the expr~ iteration to make a vanilla sample counter, i would replace rpole~ with that for counting samples, because rpole~ seems to stop counting after something like 4 minutes...
and, for short expressions [expr] is great, but for long, or complicated expressions it can be more handy to use lua scripts with ofelia.

@Jona Many thanks. Yes i agree with you. I think you need to use something more advance or complicated tricks to do something similar. I need to learn more about Ofelia. I will also check your ideas. Thanks

Robert