Dynamic argument types

It would be really neat to have a feature similar to cmdr, where you can essentially get the input from a certain argument. This is useful for data commands, and dynamically updating their type depending on what the previous argument is. For example, I have a command called `/data set`, with 2 arguments, the `dataName` and the `dataValue`, it would be nice to dynamically update the type for `dataValue` to accept the value of what `dataName` is. So if `dataName` is "coins", the dataValue should be a number. etc.