Pi

func pi(callback) {
    var (q, r, t, k, n, l) = (1, 0, 1, 1, 3, 3)
    loop {
        if ((4*q + r - t) < n*t) {
            callback(n)
            static _dot = callback('.')
            var nr = 10*(r - n*t)
            n = ((10*(3*q + r)) // t - 10*n)
            q *= 10
            r = nr
        }
        else {
            var nr = ((2*q + r) * l)
            var nn = ((q*(7*k + 2) + r*l) // (t*l))
            q *= k
            t *= l
            l += 2
            k += 1
            n = nn
            r = nr
        }
    }
}

STDOUT.autoflush(true)
pi(func(digit){ print digit })