RFC: Tab completions that are sensitive to already specified function arguments

Thanks for the hint to the existing REPL functions, I’ll have to take a more thorough look before I can say whether they’d be suitable for what I’m envisioning.

@pfitzseb have you maybe come across this type of completion before, that is context dependent on an already specified argument, like a dataframe in first position? As I’m using Juno I’d be interested in a solution that works there as well.