class Steep::AST::Types::Union

def self.build(types:, location: nil)
  return AST::Types::Bot.new if types.empty?
  return types.first if types.size == 1
  types.flat_map do |type|
    if type.is_a?(Union)
      type.types
    else
      [type]
    end
  end.map do |type|
    case type
    when AST::Types::Any
      return AST::Types::Any.new(location: location)
    when AST::Types::Top
      return AST::Types::Top.new(location: location)
    when AST::Types::Bot
      nil
    else
      type
    end
  end.compact.uniq.yield_self do |tys|
    case tys.size
    when 0
      AST::Types::Bot.new
    when 1
      tys.first
    else
      new(types: tys, location: location)
    end
  end
end

def ==(other)
  other.is_a?(Union) &&
    Set.new(other.types) == Set.new(types)
end

def free_variables
  @fvs ||= Set.new.tap do |set|
    types.each do |type|
      set.merge(type.free_variables)
    end
  end
end

def hash
  @hash ||= self.class.hash ^ types.sort_by(&:to_s).hash
end

def initialize(types:, location: nil)
  @types = types
  @location = location
end

def level
  [0] + level_of_children(types)
end

def subst(s)
  self.class.build(location: location, types: types.map {|ty| ty.subst(s) })
end

def to_s
  "(#{types.map(&:to_s).join(" | ")})"
end

def with_location(new_location)
  self.class.new(types: types, location: new_location)
end