stream.rb

class Stream
	def initialize(&more)
		@sofar = []
		@more = more
	end

	def [](i)
		while i >= @sofar.length do
			@sofar += @more.call(@sofar)
		end
		@sofar[i]
	end

	def iterator() Iterator.new(self) end
end

class Iterator
	def initialize(s)
		@s = s
		@i = -1
	end

	def next()
		@i += 1
		@s[@i]
	end
end

class Durable
	def initialize(value, duration)
		@value = value
		@duration = duration
	end

	attr_reader :value, :duration
end

# Take a Stream of Durable things, and produce a new Stream by adding up the
# durations of neighbors with the same value.
def coalesce(sd)
	iterator = sd.iterator
	current = iterator.next
	Stream.new do
		value = current.value
		duration = 0
		while current.value == value do
			duration += current.duration
			current = iterator.next
		end
		[Durable.new(value, duration)]
	end
end