Many language implementations come with an ''interactive mode''.

This is a [[wp:command-line interpreter|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 ''[[wp:read-eval-print loop|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 &nbsp; (the 3<sup>rd</sup> argument).


;Example:
            <big>  f('Rosetta',  'Code',  ':')  </big>
should return
            <big>  'Rosetta::Code'              </big>


;Note:
This task is &nbsp; ''not'' &nbsp; about creating your own interactive mode.
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