I am a little confused with this two functions: AppendTo adds and resets the variable while Reap and Sow have the attribute Hold and do not return unless finished:

t = Flatten[Reap[For[i = 1, i < 40, i++, Drop[t,{3}]; Print[t]; Sow[i]]][[2]]] 

This will print just t 40 times, not iteratively.

How can I construct a list so that it would update variable in a process of creation as some operations needs to be performed on it meanwhile? This is straightforward with AppendTo but not so with Reap or anything else.

Thanks.