use coroutine to implement producer-consumer

producer-consumer-coroutine.lua

function consumer(prod)
    while true do
        local x = receive(prod)
        print(x)
    end
end

function receive(prod)
    local status, value = coroutine.resume(prod)
    return value
end

function send(x)
    coroutine.yield(x) -- go back to where resumed
end

function producer()
	return coroutine.create(function()
		while true do
			local x = io.read()
			send(x)
		end
	end)
end

-- consumer-driven design
consumer(producer())

producer-consumer-loop.lua

function produce()
	return io.read()
end

function consume(x)
	print(x)
end

while true do
    local x = produce()
	consume(x)
end

recursiveproducer-consumer-coroutine.lua

function send(a)
	coroutine.yield(a)
end

function receive(prod)
	local status, value = coroutine.resume(prod)
	return value
end

function consumer(prod)
	local function print_result(a)
		for _, v in ipairs(a) do
			io.write(v, " ")
		end
		io.write('\n')
	end
	
	while true do
		local a = receive(prod)
		if not a then break end
		print_result(a)
	end
end


function producer(a)
	function permgen(a, n)
		if n == 0 then
			send(a) -- send something for consuming from an recursive call
		else
			for i=1, n do
				a[n], a[i] = a[i], a[n]
				permgen(a, n-1)
				a[n], a[i] = a[i], a[n]
			end
		end
	end

	local n = table.getn(a)
	return coroutine.create(function() permgen(a, n) end)
end

consumer(producer({1,2,3,4}))