bibi, it's great that you want to help out, but may I suggest that you start with something more simple than adding support for FOR-IN-DO?
E.g. start by changing the COPY command to KOPI. It is a fairly simple change to the code, but you will learn A LOT about how to develop for DOSBox in the process. Next see if you can create say ... ERASE, as an alias for DELETE. Again, fairly simple, but you will learn a lot in the process. Once you have mastered this, you are ready to tackle the larger task of adding FOR-IN-DO.
Also, here are some pointers to get you started:
http://dosbox.sourceforge.net/wiki/index.php? … =BuildingDOSBox
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