I read this as "type inference _in_ Scratch" and thought: that language for kids is getting pretty sophisticated!
I wish I could find some examples in Kotlin or Rust or Python. Something non-functional
As the language written or checked?
You only ever find tutorials on writing type checkers in things like haskell or similar.
It is often like that owl joke in art. "Step one draw a circle, step two draw some triangles, step three draw the rest of the fucking owl" and its hard to get into step 3
When I have the bandwidth I'll take a look at the video and see if I can translate.