# Stream的Ruby实现

```class Stream
def initialize(head = nil, tail = nil)
@tailFunc = tail
end

def empty?
end

end

def tail
@tailFunc.call
end

def length
count = 0
walk { count += 1}
return count
end

return zip(s2) {|x, y| x + y}
end

def substract(s2)
return zip(s2) {|x, y| x - y}
end

def times(s2)
return zip(s2) {|x, y| x * y}
end

def zip(s2, &amp;block)
return s2 if empty?
return self if s2.empty?
end

def take(count)
return self if empty?
return Stream.new if count == 0
return Stream.new(head, lambda { tail.take(count - 1) })
end

def map(&amp;block)
return self if empty?
return Stream.new(block.call(head), lambda { tail.map(&amp;block) })
end

def scale(factor)
return map { |x| x * factor}
end

def filter(&amp;block)
return self if empty?
return tail.filter(&amp;block)
end

def drop(count)
return self if empty?
s = self
count.times {s = s.tail}
return s
end

def member?(item)
s = self
s = s.tail until s.empty? || s.head == item
end

def force
s = self
s = s.tail until (s.empty?)
end

def walk(&amp;block)
map { |s| block.call(s); s }.force
end

def print
walk { |s| puts s}
end

def item(index)
s = self
index.times { s = s.tail}
end

def sum
return reduce(0) {|sum, new| sum + new}
end

def reduce(init, &amp;block)
return init if empty?
end

def Stream.range(low = 1, high = nil)
return Stream.make(low) if low == high
return Stream.new(low, lambda { Stream.range(low + 1, high) })
end

def Stream.make(*args)
return Stream.new if args.empty?
return Stream.new(args.shift, lambda { Stream.make(*args) })
end

def Stream.make_ones
return Stream.new(1, lambda { Stream.make_ones })
end

def Stream.make_natural_nums
end

def Stream.make_fib_nums_drop1
end

def Stream.make_fib_nums
return Stream.new(0, lambda { Stream.make_fib_nums_drop1 })
end

def Stream.make_factor
return Stream.new(1, lambda {  Stream.make_natural_nums.drop(1).times(Stream.make_factor) })
end
end

Stream.make_factor.take(10).print

```

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