pretty_yaml

#!/usr/bin/env ruby
require 'yaml'

def yaml_to_scalar(node, anchors={})
  case node
  when Psych::Nodes::Scalar
    node.value
  when Psych::Nodes::Document
    node.children.map do |child|
      yaml_to_scalar(child, anchors)
    end
  when Psych::Nodes::Mapping
    hash = {}
    node.children.each_slice(2) do |key, value|
      k = yaml_to_scalar(key, anchors)
      v = yaml_to_scalar(value, anchors)
      if k == '<<'
        hash = hash.merge(v)
      else
        hash[k] = v
      end
    end
    anchors[node.anchor] = hash if a = node.anchor
    hash
  when Psych::Nodes::Sequence
    ary = []
    node.children.each do |child|
      ary << yaml_to_scalar(child, anchors)
    end
    anchors[node.anchor] = ary if a = node.anchor
    ary
  when Psych::Nodes::Alias
    anchors[node.anchor]
  else
    node
  end
end
pp yaml_to_scalar(YAML.parse(ARGF.read)).first