tests/fail/demo_sieve.lua

-- sieve.lua

-- the sieve of Eratosthenes programmed with coroutines

-- typical usage: lua -e N=1000 sieve.lua | column

-- generate all the numbers from 2 to n

function gen (n)

  return coroutine.wrap(function ()

    for i=2,n do coroutine.yield(i) end

  end)

end

-- filter the numbers generated by `g', removing multiples of `p'

function filter (p, g)

  return coroutine.wrap(function ()

    while 1 do

      local n = g()

      if n == nil then return end

      if math.mod(n, p) ~= 0 then coroutine.yield(n) end

    end

  end)

end

N=N or 1000		-- from command line

x = gen(N)		-- generate primes up to N

while 1 do

  local n = x()		-- pick a number until done

  if n == nil then break end

  print(n)		-- must be a prime number

  x = filter(n, x)	-- now remove its multiples

end