This is an interesting trick as it processes your file as if it
was user input in an interactive session. As a result, all Pry
commands are available, and they are executed non-interactively. Furthermore
the session becomes interactive when the repl loop processes a
'make-interactive' command in the file. The session also becomes
interactive when an exception is encountered, enabling you to fix
the error before returning to non-interactive processing with the
'make-non-interactive' command.
John Mair