#  access_control :DEFAULT => '!guest' 
#                [:new, :create, :update, :edit] => '(admin | user | moderator)',
#                 :delete => 'admin & (!moderator & !blacklist)'
# 'admin & !(blacklist | moderator)'
# '(admin | moderator) & blacklist',
# '(admin) & (moderator & ((user | school)))'
 
grammar AclGrammar
  rule roles
    ('('? (not / and / or / role) ')'?)+
  end
 
  rule or
    left:role space '|' space right:roles
  end
 
  rule and
    left:role space '&' space right:roles
  end
 
  rule not
    '!' space roles
  end
 
  rule role
    space role:([a-zA-Z0-9]+) space
  end
 
  rule space
    [\s\r\n\t]*
  end
end