I'll write a detailed explanation as soon as I can, but for now:
Phreak.parse! is an alias to Phreak.parse(ARGV). That method creates a
Parser, which is an extended Subparser. After initialization, parse yields
the Parser, which allows bindings to be created by the user.
Finally, Phreak#parse invokes Parser#begin_parsing,
a protected method that either calls the default action, or invokes the process_token
function on itself, which is inherited from Subparser, depending on the number of
arguments that were provided.
My apologies for such a short explanation, but I'm an engineering student, so my time is quite limited. I'll do my best to fix this soon.