Generates the tree of Ruby core classes that aren't themselves in any modules

core-class-hiearchy.rb

# Writes the class hierarchy of the core Ruby classes.

$nodes = Hash.new

module Hack # Hack to keep Node out of the result!
  class Node
    attr_reader :cls 
    attr_accessor :children
    def initialize(c)
      @cls = c
      @children = []
    end
  end
end

def node_for(c)
  $nodes[c] = Hack::Node.new c if not $nodes.has_key?(c)
  $nodes[c]
end
    
def modules_in(c)
  result = c.included_modules
  (c.ancestors - [c]).each {|a| result -= a.included_modules}
  result
end

def pretty_list(a)
  a.empty? ? "" : "(#{a.join(',')})"
end

def print_tree(n, indent = "")
  puts("#{indent}#{n.cls.name} #{pretty_list(modules_in(n.cls))}")
  n.children.each do |child|
    print_tree(child, indent + "    ")
  end
end

Module.constants.each do |constant|
  c = Kernel.const_get(constant)
  if Class === c
    n = node_for c
    if c.superclass
      s = node_for(c.superclass)
      s.children << n
    end
  end
end

print_tree(node_for(BasicObject))