Many language implementations come with an interactive mode.

This is a command-line interpreter that reads lines from the user and evaluates these lines as statements or expressions.

An interactive mode may also be known as a command mode,   a read-eval-print loop (REPL),   or a shell.



Task

Show how to start this mode.

Then, as a small example of its use, interactively create a function of two strings and a separator that returns the strings separated by two concatenated instances of the separator   (the 3rd argument).



Example

             f('Rosetta',  'Code',  ':')   

should return

             'Rosetta::Code'               



Note

This task is   not   about creating your own interactive mode.




 > quackery

Welcome to Quackery.

Enter "leave" to leave the shell.

/O> say " now entering a nested shell..."
... shell
... 
 now entering a nested shell...
/O> say " now leaving the nested shell"
... leave
... 
 now leaving the nested shell
Auf wiedersehen.


Stack empty.

/O> say " now leaving the shell invoked at the command line"
... leave
... 
 now leaving the shell invoked at the command line
Goodbye.


 > echo " back at the command line"
 back at the command line
 >