I am trying to change my vimrc to vim9script. For inbuilt fortran help, (:h fortran) we have:

:let fortran_free_source=1

This is giving an error:

E1126: Cannot use :let in Vim9 script

If I remove the let, I am getting:

E492: Not an editor command:    fortran_free_source = 1

How should I update this?

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1 Answer 1


In general you have to declare the variable once using var


var fortran_free_source = 1

is the equivalent of:

let s:fortran_free_source=1

After the variable has been declared you can modify it without using let.


var fortran_free_source = 1

# I change my mind:
fortran_free_source = 0

But if you want to change a global variable they need not to be declared hence:


# Set a global variable:
g:fortran_free_source = 1

is the equivalent of:

" Set a global variable:
let g:fortran_free_source=1
  • 4
    I think in this case it should just be: g:fortran_free_source = 1. Globals are not declared with "var" and the spaces around the equal sign are required.
    – Heptite
    Aug 27, 2022 at 4:27
  • Thanks @Heptite :-) I have adapted the solution accordingly. Aug 27, 2022 at 4:39
  • 1
    I would reword: "is equivalent of:" -- it is not. It would be the same as let s:fortran_free_source
    – Maxim Kim
    Aug 27, 2022 at 6:04
  • Thanks @Maxim, I was hesitating since if you are in a function I suppose x = 1 is equivalent to let a:x, let v:x = 1 or let s:x depending if x is a function argument n local variable or a script variable. Aug 27, 2022 at 6:22
  • 1
    let somevar = 1 in a function would be let l:somevar, in a script let s:somevar (provided there were no global var with the same name defined beforehand)
    – Maxim Kim
    Aug 27, 2022 at 6:29

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