Adapted from the unparser usage example, at https://github.com/mbj/unparser#usage

unparse.rb

require 'parser/current'
require 'unparser'
require 'byebug'

module YourHelper
  def s(type, *children)
    Parser::AST::Node.new(type, children)
  end
end

include YourHelper

# begin experiments

node = s(:def,
  :foo,
  s(:args,
    s(:arg, :x)
  ),
  s(:send,
    s(:lvar, :x),
    :+,
    s(:int, 3)
  )
)

Unparser.unparse(node) # => "def foo(x)\n  x + 3\nend"

byebug

puts "eof" # byebug won't pause execution if it's the last line of code