function f(a)
printh("f",a)
return yield (2*a)
end

co = cocreate(function(a,b)
    printh("co1",a,b)
    local r = f(a+1)
    printh("co2", r)
    local r,s = yield(a+b,a-b)
    printh("co3",r,s)
    return b, "end"
end)

printh("m1",coresume(co,1,10))
printh("m2",coresume(co,"r"))
printh("m3",coresume(co,"x","y"))
printh("m4",coresume(co,"x","y"))