default.rb

foo do
  bar :baz
end

foo.rb

define :foo do
  log "got params[:bar] = #{params[:bar].inspect}"
  other do
    inner params[:bar]
    inner2 :buzz
  end
end

other.rb

define :other do
  log "in other params[:inner] = #{params[:inner].inspect}"
  log "in other params[:inner2] = #{params[:inner2].inspect}"
end

output

[2012-12-19T16:08:38+00:00] INFO: got params[:bar] = :baz
[2012-12-19T16:08:38+00:00] INFO: in other params[:inner] = nil
[2012-12-19T16:15:54+00:00] INFO: in other params[:inner2] = :buzz