def repeat(n, fn = ->x{x})
[n, ->{repeat(fn.call(n), fn)}]
end
def map(mapper, stream)
[mapper.call(stream.first), stream.last.nil? ? nil : ->{map(mapper, stream.last.call)}]
end
def take(n, stream)
[stream.first, n == 1 ? nil : ->{take(n - 1, stream.last.call)}]
end
def drop(n, stream)
if n.zero?
stream
else
drop(n - 1, stream.last.call)
end
end
def realize(n, stream)
if n.zero?
[]
else
[stream.first] + if stream.last.nil?
[]
else
realize(n - 1, stream.last.call)
end
end
end
p realize(20, map(->x{Rational(1, x)}, take(10, drop(1000, repeat(1, ->x{x + 1})))))
