-- In Lua 5.1 you can't yield over a pcall.

-- feature test
local function has_yieldable_pcall(pcall)
	-- This has to happen inside a throwaway coroutine, as if the
	-- feature works, we don't want to yield back to whatever called us.
	-- You have to pass coroutine.create an actual lua function,
	-- so coroutine.create; a C function won't do.
	local ok, has = coroutine.resume(coroutine.create(function()
		-- Pass `true` so we don't need to fix up `has`
		return pcall(coroutine.yield, true)
	end))
	-- throw error if feature detection fails
	assert(ok, has)
	return has
end

if not has_yieldable_pcall(pcall) then
	local function helper(co, ok, ...)
		if ok then
			return helper(co, coroutine.resume(co, coroutine.yield(...)))
		else
			return false, (...)
		end
	end

	function pcall(func, ...)
		-- You have to pass coroutine.create an actual lua function,
		-- so coroutine.create; a C function won't do.
		local co = coroutine.create(function(...) return func(...) end)
		return helper(co, coroutine.resume(co, ...))
	end
end


local function foo(arg)
	assert(arg == "a")
	assert(coroutine.yield("1") == "b")
	assert(coroutine.yield("2") == "c")
	return "3"
end
do
	local co = coroutine.create(foo)
	assert(select(2, assert(coroutine.resume(co, "a"))) == "1")
	assert(select(2, assert(coroutine.resume(co, "b"))) == "2")
	assert(select(2, assert(coroutine.resume(co, "c"))) == "3")
end
do
	local function bar(...)
		return select(2, assert(pcall(foo, ...)))
	end
	local co = coroutine.create(bar)
	assert(select(2, assert(coroutine.resume(co, "a"))) == "1")
	assert(select(2, assert(coroutine.resume(co, "b"))) == "2")
	assert(select(2, assert(coroutine.resume(co, "c"))) == "3")
end

do
	local co = coroutine.create(function()
		local ok, err = pcall(function()
			error("OK", 0)
		end)
		assert(not ok and err == "OK")
	end)
	assert(coroutine.resume(co, "a"))
end

do
	local co = coroutine.create(function()
		return "1"
	end)
	assert(select(2, assert(coroutine.resume(co, "a"))) == "1")
	assert(select(2, assert(coroutine.resume(co, "a"))) == "1")
end