You have to declare the variable as `var` as well, eg. var arr1 = [4, 2, 3, 6] sort arr1 # Doesn't work let arr2 = [4, 2, 3, 6] sort arr2

You have to declare the variable as `var` as well, eg. var arr1 = [4, 2, 3, 6] sort arr1 # Doesn't work let arr2 = [4, 2, 3, 6] sort arr2 You'll get a warning about the latter from the compiler (and nimsuggest for editors).