aboutsummaryrefslogtreecommitdiff
blob: 0871bb212592726d5cca2c9478e9fcaf12c8ff09 (plain)
1
2
3
4
5
6
7
8
9
10
11
12
13
14
15
16
17
18
19
20
21
22
23
24
25
26
27
28
29
-- 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