Yes, it is possible to write games in the Progress 4GL and no, indeed, it is not logical to do so. That's why I did it :) Just because I can.
Writing games in Progress is fun to do. It is different than the day to day chores and sometimes asks different skills than what is required for 'normal' applications.
This game was originally written by me in march 2000. Recently I found it back on an old drive and decided it was fun to blow the dust off of it. There were a few small bugs in the code that were too hard for me to fix back then. In 2017, it took me a matter of minutes to repair the code. Apparently, my skills have improved a bit in the last few years.
Anyway, try the program in your progress editor. Just place it somewhere and run it with a full path, so if you place it in c:\progress\sokoban then just do:
run c:\progress\sokoban\sokoban.p