1 files changed, 29 insertions, 0 deletions
diff --git a/test/sieve.lua b/test/sieve.lua
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+-- 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