1-- the sieve of of Eratosthenes programmed with coroutines 2-- typical usage: lua -e N=1000 sieve.lua | column 3 4-- generate all the numbers from 2 to n 5function gen (n) 6 return coroutine.wrap(function () 7 for i=2,n do coroutine.yield(i) end 8 end) 9end 10 11-- filter the numbers generated by `g', removing multiples of `p' 12function filter (p, g) 13 return coroutine.wrap(function () 14 while 1 do 15 local n = g() 16 if n == nil then return end 17 if math.mod(n, p) ~= 0 then coroutine.yield(n) end 18 end 19 end) 20end 21 22N=N or 1000 -- from command line 23x = gen(N) -- generate primes up to N 24while 1 do 25 local n = x() -- pick a number until done 26 if n == nil then break end 27 print(n) -- must be a prime number 28 x = filter(n, x) -- now remove its multiples 29end 30