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

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

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

function filter (prod)
        return coroutine.create( function ()
                local line = 1
                while true do
                        local x = receive(prod)
                        x = string.format("%5d %s", line, x)
                        send(x)
                        line = line + 1
                end
        end)
end

function consumer (prod)
        while true do
                local x = receive(prod)
                io.write(x, "\n")
        end
end

p = producer()  -->creates a coroutine p, which yield after read a line from stdio agin and agin
f = filter(p)   -->creates a coroutine f, which resume the p at first and yeild after the string processed
consumer(f)     -->resumes the coroutine f, and writes the string f processed