I&#x27;ve sometimes wondered about using Forth-style stack manipulation as the basis for a game, and it&#x27;s nice to see someone do it.<p>These are the things that weren&#x27;t clear to me, and that I had to spend a couple of minutes randomly clicking around to figure out (bearing in mind I&#x27;m somebody who already knows what a stack machine is supposed to be doing):<p>- &quot;proceed to the next level&quot; means: click the up-arrow at the bottom right of the window.<p>- Levels are completed by filling in the grey tiles in the centre of the window, and running the program.<p>- Filling in those tiles is done by draging smaller grey tiles from the top-left corner.<p>- The program can be run by clicking the right-arrow at the bottom of the window.<p>- The first proper level (called &quot;0_0&quot;, as far as I can tell) is already complete, the reason you can&#x27;t do anything is because there&#x27;s nothing to be done.