first?

first? is a predicate to test the call is a first call to first? with current group.

It is useful to format comma separated values as:

q.group(1, '[', ']') {
  xxx.each {|yyy|
    unless q.first?
      q.text ','
      q.breakable
    end
    ... pretty printing yyy ...
  }
}

first? is obsoleted in 1.8.2.