A self building text adventure game which starts off with an empty world:
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You build new places with “build my house n” (which means build my house to the north) then you can go there “n” and give it a description “describe a blue house with red doors”. You can also make objects with eg “make cheese” and take it (when it will be added to your inventory), move around and drop it elsewhere.
If you type “dot” you get a text description of the world which can be read by graphviz. Here is part of my mental model of Helsinki: