Pinescript – variable set to 0 returns a non zero value when referenced with an index

I’m having an hard time debugging a Pinescript indicator. Here is the code

//@version=4
study("Trend Regularity Adaptive Moving Average","TRAMA",overlay=true)
length=input(99),src = input(close)
//----
ama = 0.
//debugging part
txt = tostring(ama[1])
x = bar_index
y = src
//end of debugging part
label.new(x, y, txt) // print value of close
hh = max(sign(change(highest(length))),0)
ll = max(sign(change(lowest(length))*-1),0)
tc = pow(sma(hh or ll ? 1 : 0,length),2)
ama := nz(ama[1]+tc*(src-ama[1]),src)
plot(ama,"Plot",#ff1100,2)

What i don’t understand is the value of ama[1]. Here ama is declared to be 0, but ama[1] returns a non zero value. From what i understood, in Pinescript [1] should return the value of the previous bar, but since in this case ama is set to be 0, how is it possible that it returns a non zero value?

>Solution :

It is because you are re-assigning a value to ama with ama := nz(ama[1]+tc*(src-ama[1]),src).

The way this works is, if ama[1]+tc*(src-ama[1]) is na, ama will be src. If it is not na, it will be ama[1]+tc*(src-ama[1]).

nz(source, replacement) → simple float

RETURNS
The value of source
if it is not na. If the value of source is na, returns zero, or
the replacement argument when one is used.

ARGUMENTS
source (series int/float/bool/color) Series of values to process.
replacement (series int/float/bool/color) Value that will replace all ‘na’ values in the source series.