Recursively generated graphs

gistfile1.rb

# A nifty class providing recursive graph generation
class Graph
  def initialize(*args, &blk)
    @edges = []
    @block = blk
    @nodes = 0
    @inited = false
    yield self, *args if block_given?
  end
  def init
    return if @inited
    @inited = true
    yield self
  end
  def recurse(*args)
    @block[self, *args] unless @block.nil?
  end
  def edge(a, b); @edges << [a, b]; end
  def nodes(n); @nodes = n; end
  def next_node!; @nodes += 1; end
  def to_s; @edges.map {|e| e * " "} * "\n"; end
end

# Example:
g = Graph.new(ARGV[0].to_i, 1, 2, 3) do |g, n, a, b, c|
  # Initial configuration: a triangle of 3 nodes
  g.init do
    g.nodes 3
    g.edge(1, 2)
    g.edge(2, 3)
    g.edge(3, 1)
  end
  
  # A recursively-generated structure
  if n > 0
    new_id = g.next_node!
    g.edge(a, new_id)
    g.edge(b, new_id)
    g.edge(c, new_id)
    
    g.recurse(n-1, a, b, new_id)
    g.recurse(n-1, a, new_id, c)
    g.recurse(n-1, new_id, b, c)
  end
end

puts g