What is script mode in V

[foliagetree23]

Either __global (it's about how to enable global mode in V), an assignment out-scope function the compiler switching to a script mode such reported by the compiler itself when running the program, i need help about this an explanation what is script mode in V or give me a link to another resource in the internet, thank you for help.

module main

a := 10

fn main_a() {

	a := 10
	println('Hello World!')
}

fn main_b() {
	a := 10

}

[JalonSolov]

It simply means V without the "fluff".

Script mode automatically imports the os module for you, so you can write simple programs without having to include a module line at the top, or any fn definitions unless you want them.

That's how you can have

println('Hello World')

as a complete V program. No module line, no fn main() { } etc. needed.

This is actually implemented in such a way that V wraps a "virtual" fn main() around your code, so the a := 10 line you have is not actually a global, it is inside main().

[foliagetree23]

Ok, understand now how script mode in V is. And there's above example such as:
main_b()

it returning as result (if such example above case could written) reporting by compiler:

main.v:6:4: error: all definitions must occur before code in script mode
    4 | 
    5 | 
    6 | fn main_a() {
      |    ~~~~~~
    7 |     a := 10
    8 | }

So, why that resulting error occur? and give me suggestions for that. For me i think this couldn't happen because it was switching into script mode, or give it another name function.
fn abc_night()

I was trying above but the reporting is same as:
main.v:6:4: error: all definitions must occur before code in script mode.

So i think i didn't understand about this error.

[JalonSolov]

It is a very explicit error, which is happening because you have a := 10 before the function definitions. In script mode, all functions, structs, etc. must occur before the first "code" (which in this case is just declaring a variable.

Your example:

module main

a := 10

fn main_a() {

	a := 10
	println('Hello World!')
}

fn main_b() {
	a := 10

}

gives the following:

$ v run x.v
x.v:3:1: notice: script mode started here
    1 | module main
    2 | 
    3 | a := 10
      | ^
    4 | 
    5 | fn main_a() {
x.v:5:4: error: all definitions must occur before code in script mode
    3 | a := 10
    4 | 
    5 | fn main_a() {
      |    ~~~~~~
    6 | 
    7 |     a := 10
$

while just moving the variable after the functions:

module main

fn main_a() {

        a := 10
        println('Hello World!')
}

fn main_b() {
        a := 10

}

a := 10

gives this output:

$ v run x.v
x.v:5:2: warning: unused variable: `a`
    3 | fn main_a() {
    4 | 
    5 |     a := 10
      |     ^
    6 |     println('Hello World!')
    7 | }
x.v:10:2: warning: unused variable: `a`
    8 | 
    9 | fn main_b() {
   10 |     a := 10
      |     ^
   11 | 
   12 | }
x.v:14:1: warning: unused variable: `a`
   12 | }
   13 | 
   14 | a := 10
      | ^
$

which is correct, as the variables were created, but never used.

[foliagetree23]

Well of course that, i see that how V is constructed for. Now i'm understanding, thank you for answering my question which explaining more about V is programming system.