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:\>rexx rexxtry ?
 This procedure lets you interactively try REXX statements.
 If you run it with no parameter, or with a question mark
 as a parameter, it will briefly describe itself.
 You may also enter a REXX statement directly on the command line
 for immediate execution and exit.  Example:  rexxtry call show

 Enter 'call show' to see user variables provided by REXXTRY.
 Enter '=' to repeat your previous statement.
 Enter '?' to invoke system-provided online help for REXX.
 The subroutine named 'sub' can be CALLed or invoked as 'sub()'.
 REXXTRY can be run recursively with CALL.

 Except for the signal instructions after a syntax error, this
 procedure is an example of structured programming.

D:\>rexx rexxtry
REXX-ooRexx_4.2.0(MT)_64-bit 6.04 22 Feb 2014
  rexxtry.rex lets you interactively try REXX statements.
    Each string is executed when you hit Enter.
    Enter 'call tell' for a description of the features.
  Go on - try a few...            Enter 'exit' to end.
x=3
  ........................................... rexxtry.rex on WindowsNT
y=x**2
  ........................................... rexxtry.rex on WindowsNT
say x y
3 9
  ........................................... rexxtry.rex on WindowsNT

  rexxtry.rex:  Enter 'exit' to end.       Or '?' for online REXX help.
say sigl
160
  ........................................... rexxtry.rex on WindowsNT
say sourceline(12)
/* Redistribution and use in source and binary forms, with or                 */
  ........................................... rexxtry.rex on WindowsNT  
exit

D:\>