Love it, especially the consistent visual distinction between Single and Multiple types - such a great idea!
That said, there’s an obvious question/enhancement raised by the examples provided: Both of them use the chips as clues to why these formulae aren’t working. How about having the evaluation UI report a helpful error instead of just returning zero? These type mismatch issues should be detectable at formula compile time.
Don’t get me wrong, I still think the chips are a great addition: they make most interactions with formulae better, not just debugging. However, what would be even better is something like this:
Please forgive me if you’re already working on something like this! I’m just copying what I’ve seen while programming in the Elm language, which gives the most helpful errors I’ve ever seen from a compiler; take a look at the Compiler Errors For Humans blog post for their design philosophy.