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.




 
$ ol
Welcome to Otus Lisp 2.1-2282-27a9b6c
type ',help' to help, ',quit' to end session.
> (define (f head tail mid)
     (string-append head mid mid tail))
;; Defined f
> (f "Rosetta" "Code" ":")
"Rosetta::Code"
> ,quit
bye-bye :/
 