That's interesting! I haven't paid much attention to Flow since trying out the initial release and finding it a bit lacking. (But then, I'm used to GHC/Haskell, so everything lacking!)

I truly feel that "disjoint unions" is one of those things you don't appreciate the true value of until you've used them for quite a while. The real eye-opener for me was implementing a state machine and finding that I could explicitly state exactly which bits of the state machine would propagate to $NEXT_STATE at every step... and have the compiler double-check for me that I got it right.

EDIT: I accidentally a accidentally.