A variation in which Yaml and JSON objects are first-class values which ...

...preserve their type, not just strings. I think this syntax is also a little easier on the eyes than the ERB - all you need to do is to start the value with an equal sign: "=".
```
    mysql_host: 127.0.0.1
    mysql_ports: [ 1001, 1002, 1003, 1004, 1005 ]
    first_two_ports: = mysql_ports[0...2]
    random_port: = mysql_ports.sample
    db_host: = "#{mysql_host}"
    db_port: = random_port
    as_url: = "mysql://#{db_host}:#{random_port}/"
    current_time: = Time.now
    # note that interpolation below is tricky becase a blank preceeding a hash #{is a Yaml comment}
    comment: = "At " + Time.now.to_s + " port " + random_port.to_s + "was chosen"
    vendor:
       name: Some Company
       email: info@example.com
    contact: = vendor["email"]
```