Function tui_terminal_ok 

pub fn tui_terminal_ok(
    stdin_tty: bool,
    stdout_tty: bool,
    term: Option<&str>,
) -> Result<(), String>

Checks that the TUI has a terminal to draw on and read keys from.

scope tui needs stdin and stdout on a terminal, and a TERM that is not dumb. Pure: the caller passes the facts.

Errors

Returns the message to print when any of them is missing.