class Hamster::Queue

def clear
  EmptyQueue
end

def dequeue
  front = @front
  rear = @rear
  if front.empty?
    return EmptyQueue if rear.empty?
    front = rear.reverse
    rear = EmptyList
  end
  transform do
    @front = front.tail
    @rear = rear
  end
end

def empty?
  @front.empty? && @rear.empty?
end

def enqueue(item)
  transform { @rear = @rear.cons(item) }
end

def eql?(other)
  instance_of?(other.class) &&
    to_list.eql?(other.to_list)
end

def head
  return @front.head unless @front.empty?
  @rear.last
end

def initialize
  @front = @rear = EmptyList
end

def inspect
  to_list.inspect
end

def size
  @front.size + @rear.size
end

def to_a
  to_list.to_a
end

def to_ary
  to_list.to_ary
end

def to_list
  @front.append(@rear.reverse)
end