-- the sieve of 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