Pluggable commands in the JShell tool

[Andrei Eremeev]

Hi REPL team,

What do you think about pluggable commands in JShell? It will allow 
users implementing their custom commands. For example, JShell can be 
used in scripting, and it is useful to run a process within it. So, a 
user can implement a command, like /run-process, and register it as a 
service.
The commands can be loaded by ServiceLoader, and they should implement 
an interface, like:

public interface Command {
     boolean run(JShellWrapper jShell, String arg);	// JShellWrapper is a class/interface which encapsulates JShellTool/JShellState
     String command();					// command name
     boolean matches(String input);			// a method to understand whether the input typed by a user is the current command
     String/List<String> parameters();			// information to be printed in the help command
     String description();				// information to be printed in the help command
     String help();					// information to be printed in the help command
     CompletionProvider completionProvider();		// a provider to suggest completions for arguments of the command
}

What do you think?

Andrei