function command( repl ) {
	return onCommand;

	/**
	* Callback invoked to confirm that a command has finished executing.
	*
	* @private
	* @param {(Error|null)} [error] - execution error
	* @param {*} [results] - command results
	* @returns {void}
	*/
	function onCommand( error, results ) {
		if ( arguments.length === 0 ) {
			return repl._done();
		}
		if ( arguments.length === 1 ) {
			return repl._done( error );
		}
		repl._done( error, results );
	}
}
Returns a callback to be invoked upon calling the `__done__` command.

@private
@param {REPL} repl - REPL instance
@returns {Function} callback