Pine Script v5 compiler report "undeclared identifier"

Question

code like this:

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

x = if open > close
    var a = 10
    var b = 20
    a := 20
    b := 30
    (a+b)[1]
plot(x)

compiler report "a" and "b" in (a+b)[1] are undeclared identifiers:

line 11: Undeclared identifier 'a';
line 11: Undeclared identifier 'b'

but 'a' and 'b' are declared in the block if modify expr '(a+b)[1]' to 'a+b', the compilation is successful. how the compiler works？

Answer 1

In my case, compiler reports the issue specifically with the a on the 11th line (in the else branch). In this case, the error is expected because the a variable was declared inside the if branch and does not exist in the else branch at all.

For this to work, you need to declare a outside of the if/else condition. Here's one possible way to rewrite this code:

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

f() =>
    var a = 10
    var b = 20
    if open > close
        a := 20
        b := 30
        (a+b)[1]
    else
        a
x = f()
    
plot(x)

Answer 2

Very often, the compiler message does not exactly match the problem, you have to guess what it is trying to say.

In this case and logically, the declarations should not be in an "if" section because the variables are accessible everywhere in the script, so you must declare them at the lowest level.

Answer 3

You can use it like (a[1]+b[1]) right in the meantime