I wrote a blog post on how Funktal handles Uxn/Varvara I/O devices and state, with examples of a few GUI-based programs.
https://wimvanderbauwhede.codeberg.page/articles/funktal-devices-state/
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More on Funktal: I/O devices and state
How Funktal programs can interact with I/O devices, and how mutable state helps with this.Wim Vanderbauwhede