I have been doing something minor - not full language - but I am working on a couple DSLs for my game engine. The games themselves are interpreted by my engine console - then transpiled to webgl and JavaScript.

The DSL is for cutscenes and scripting dialogues and movements and transitions.

The idea was to have a screenplay like language that would run in my game engine so I can write the scenes like a script instead of like code.

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Then I am using a LUA like subset for the core game logic.

I don’t think I would want to have the entire thing written in a custom language though, as that seems unnecessary