Comment 4 for bug 1655800

--- The IDE resets almost all of its state between runs
... not really (see comment below), but the script is always run from beginning and hence the state before the newest line added is created again.

So I admit, that it is not really a REPL, but more some incremental scripting support ;-)

On the other hand:
On the wishlist for the IDE there is a feature, to run only portions of a script. This can be augmented in your direction, in that there is an option to run the selected code (the new line added in your case) without resetting anything.

comment on "The IDE resets almost all of its state between runs":
On rerun in fact nothing (e.g. variable contents defined) in the script is reset, only some SikuliX environment settings and with version 1.1.1 imports of SikuliX scripts are refreshed now (to avoid this ugly reload()).