property _sum
property _func
property _timeLast
property _valueLast
property _ms0
property _updateTimer

on new (me, func)
    if voidP(func) then func = "0.0"
    me._sum = 0.0
    -- update frequency: 100/sec (arbitrary)
    me._updateTimer = timeout().new("update", 10, #_update, me)
    me.input(func)
    return me
end

on stop (me)
    me._updateTimer.period = 0 -- deactivates timer
end

-- func is a term (as string) that might contain "t" and is evaluated at runtime
on input (me, func)
    me._func = func
    me._ms0 = _system.milliseconds
    me._timeLast = 0.0
    t = 0.0
    me._valueLast = value(me._func)
end

on output (me)
    return me._sum
end

on _update (me)
    now = _system.milliseconds - me._ms0
    t = now/1000.0
    val = value(me._func)
    me._sum = me._sum + (me._valueLast+val)*(t - me._timeLast)/2
    me._timeLast = t
    me._valueLast = val
end