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.




D:\projects\Bracmat>bracmat
Bracmat version 5, build 105 (1 December 2011)
Copyright (C) 2002 Bart Jongejan
Bracmat comes with ABSOLUTELY NO WARRANTY; for details type `!w'.
This is free software, and you are welcome to redistribute it
under certain conditions; type `!c' for details.



{?} get$help { tutorial }
{?} )        { stop }
{?} (f=a b c.
{1}   !arg:(?a,?b,?c)
{1}   & str$(!a !c !b)
{1}   )
{!} f
    S   0,00 sec  (2156.2173.0)
{?} f$(Rosetta,Code,":")
{!} Rosetta:Code
    S   0,00 sec  (2156.2173.0)
{?}