what is historical value for series that define in user-build function in pine script5?

Question

I have code below. this is a user-built function. we pass "close" to "src" as an input. i know "src" and "atr" are series. so "up" is series too. after that "upper" is series too.

myfunc(src,length,mult)=>
atr = ta.atr(length)*mult
up = hl2 + atr
upper = 0.
upper := src[1] < upper[1] ? math.min(up,upper[1]) : up

now my question is what is the value of upper[1] when we compare it with src[1]? we dont have any calculation for measuring last values of "upper" before? is all previous values of "upper" equal to zero because we declare it like upper=0. ?

Answer 1

Functions have their own local scope and the historical values are available too just like if it was a global scope.

See below example:

//@version=5
indicator("My script")

foo() =>
    a = 0
    a := nz(a[1]) + 1

a = foo()

plot(a)

On the first bar, a is zero and it will return 1 because 0 + 1 = 1.

On the second bar, it will access the historical value of a[1], which is 1 and then add 1 to it. So, it will return 2.

And so on.