$ composer require psy/psysh:@stable

$ ./vendor/psy/psysh/bin/psysh 
Psy Shell v0.8.0 (PHP 7.1.0 — cli) by Justin Hileman
>>> help
  help       Show a list of commands. Type `help [foo]` for information about [foo].      Aliases: ?                     
  ls         List local, instance or class variables, methods and constants.              Aliases: list, dir             
  dump       Dump an object or primitive.                                                                                
  doc        Read the documentation for an object, class, constant, method or property.   Aliases: rtfm, man             
  show       Show the code for an object, class, constant, method or property.                                           
  wtf        Show the backtrace of the most recent exception.                             Aliases: last-exception, wtf?  
  whereami   Show where you are in the code.                                                                             
  throw-up   Throw an exception out of the Psy Shell.                                                                    
  trace      Show the current call stack.                                                                                
  buffer     Show (or clear) the contents of the code input buffer.                       Aliases: buf                   
  clear      Clear the Psy Shell screen.                                                                                 
  history    Show the Psy Shell history.                                                  Aliases: hist                  
  exit       End the current session and return to caller.                                Aliases: quit, q               
>>> 

>> $arr = [1,2,3];
=> [
     1,
     2,
     3,
   ]
>>> 1 + 2;
=> 3
>>> function square($x) {
... return $x*$x*$x;
... }
=> null
>>> square(4);
=> 64