how to idioms

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