fabonacci tail call optimization
// n, n -1 , n-2
//
fun(left, 0) {
return f(n-1) +f(n-2)
}
fun(n[], pre =0) {
pop
return ()
}
// fabonacci 数列 1,1, 2, 3, 5, 8, 0 1 2 3
===================
fn()
if(m ===1, )
return f(n-1, current, current + ac)acc , acc2 ,
acculate