If you are using PHP 7.3 installed by homebrew on Mojave, try creating a config file at ~/.config/psysh/config.php if not already there:

<?php
return [
  'usePcntl' => false,
]; 

Source: https://github.com/bobthecow/psysh/issues/540#issuecomment-446480753

https://stackoverflow.com/questions/53773098/php-artisan-tinker-crashing-from-any-command