义齿

協程についてまだ深く認識していないので、いくつか例を貼っておきましょう.
luaが記述したコヒーレンス例:yieldのパラメータはresumeによって返され、resumeのパラメータはyieldによって返される.

function foo (a)
	print("foo", a)
	return coroutine.yield(2*a)
end
 
co = coroutine.create(function (a,b)
		print("co-body", a, b)
		local r = foo(a+1)
		print("co-body", r)
		local r, s = coroutine.yield(a+b, a-b)
		print("co-body", r, s)
		return b, "end"
	end)
		
print("main", coroutine.resume(co, 1, 10))
print("main", coroutine.resume(co, "r"))
print("main", coroutine.resume(co, "x", "y"))
print("main", coroutine.resume(co, "x", "y"))

出力結果:

co-body 1       10
foo     2

main    true    4
co-body r
main    true    11      -9
co-body x       y
main    true    10      end
main    false   cannot resume dead coroutine

第2例

coro = {}

coro.main = function() end
coro.current = coro.main

function coro.create(f)
   return coroutine.wrap(function(val)
                            return nil,f(val)
                         end)
end

function coro.transfer(k,val)
   if coro.current ~= coro.main then
      return coroutine.yield(k,val)
   else
      while k do
         coro.current = k
         if k == coro.main then
            return val
         end
         k,val = k(val)
      end
      error("coroutine ended without transfering control...")
   end
end

function foo1(n)
   print("1: foo1 received value "..n)
   n = coro.transfer(foo2,n + 10)
   print("2: foo1 received value "..n)
   n = coro.transfer(coro.main,n + 10)
   print("3: foo1 received value "..n)
   coro.transfer(coro.main,n + 10)
end

function foo2(n)
   print("1: foo2 received value "..n)
   n = coro.transfer(coro.main,n + 10)
   print("2: foo2 received value "..n)
   coro.transfer(foo1,n + 10)
end

function main()
   foo1 = coro.create(foo1)
   foo2 = coro.create(foo2)
   local n = coro.transfer(foo1,0)
   print("1: main received value "..n)
   n = coro.transfer(foo2,n + 10)
   print("2: main received value "..n)
   n = coro.transfer(foo1,n + 10)
   print("3: main received value "..n)
end

coro.main = main
coro.current = coro.main
coro.main()

coroutineについて.wrap、ヘルプドキュメントには次のセクションがあります.
wrapで作成されたcoroutineは、呼び出し時にresume機能と似ています.渡されたパラメータはyieldの戻り値として、yield文が実行されるとwrap関数の戻り値が生成されます.

Like coroutine.create, the coroutine.wrap function also creates a coroutine, but instead of returning the coroutine itself, 
it returns a function that, when called, resumes the coroutine. Any arguments passed to this function go as extra arguments 
to coroutine.resume. coroutine.wrap returns all the values returned by coroutine.resume, except the first one (the boolean 
error code). Unlike coroutine.resume, coroutine.wrap does not catch errors; any error is propagated to the caller. 

実行結果を添付:

1: foo1 received value 0
1: foo2 received value 10
1: main received value 20
2: foo2 received value 30
2: foo1 received value 40
2: main received value 50
3: foo1 received value 60
3: main received value 70