Filter

The way you configure your terminal behavior; a trivial wrapper around a function, though you should provide a good .toString method to make debugging easier. The TermInfo and TermAction types are its interface to the terminal.

Filters are composed sequentially: if a filter returns None the next filter is tried, while if a filter returns Some that ends the cascade. While your op function interacts with the terminal purely through immutable case classes, the Filter itself is free to maintain its own state and mutate it whenever, even when returning None to continue the cascade.