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# frozen_string_literal: true
require 'psych/nodes/node'
require 'psych/nodes/stream'
require 'psych/nodes/document'
require 'psych/nodes/sequence'
require 'psych/nodes/scalar'
require 'psych/nodes/mapping'
require 'psych/nodes/alias'
module Psych
###
# = Overview
#
# When using Psych.load to deserialize a YAML document, the document is
# translated to an intermediary AST. That intermediary AST is then
# translated in to a Ruby object graph.
#
# In the opposite direction, when using Psych.dump, the Ruby object graph is
# translated to an intermediary AST which is then converted to a YAML
# document.
#
# Psych::Nodes contains all of the classes that make up the nodes of a YAML
# AST. You can manually build an AST and use one of the visitors (see
# Psych::Visitors) to convert that AST to either a YAML document or to a
# Ruby object graph.
#
# Here is an example of building an AST that represents a list with one
# scalar:
#
# # Create our nodes
# stream = Psych::Nodes::Stream.new
# doc = Psych::Nodes::Document.new
# seq = Psych::Nodes::Sequence.new
# scalar = Psych::Nodes::Scalar.new('foo')
#
# # Build up our tree
# stream.children << doc
# doc.children << seq
# seq.children << scalar
#
# The stream is the root of the tree. We can then convert the tree to YAML:
#
# stream.to_yaml => "---\n- foo\n"
#
# Or convert it to Ruby:
#
# stream.to_ruby => [["foo"]]
#
# == YAML AST Requirements
#
# A valid YAML AST *must* have one Psych::Nodes::Stream at the root. A
# Psych::Nodes::Stream node must have 1 or more Psych::Nodes::Document nodes
# as children.
#
# Psych::Nodes::Document nodes must have one and *only* one child. That child
# may be one of:
#
# * Psych::Nodes::Sequence
# * Psych::Nodes::Mapping
# * Psych::Nodes::Scalar
#
# Psych::Nodes::Sequence and Psych::Nodes::Mapping nodes may have many
# children, but Psych::Nodes::Mapping nodes should have an even number of
# children.
#
# All of these are valid children for Psych::Nodes::Sequence and
# Psych::Nodes::Mapping nodes:
#
# * Psych::Nodes::Sequence
# * Psych::Nodes::Mapping
# * Psych::Nodes::Scalar
# * Psych::Nodes::Alias
#
# Psych::Nodes::Scalar and Psych::Nodes::Alias are both terminal nodes and
# should not have any children.
module Nodes
end
end
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