Fortran code should conform to the Fortran 2008 standard and should use an indentation level of 2, except for the extra indentation within do if, select or where statements and for each level inside a structure e.g. type, interface, where the indentation level is 3, and a 0 indentation is used for module or contains (except for contains inside a derived type, where a single indentation level is used).

These are the default rules in Emacs' Fortran mode, an example is given below,

module example
  use mod
  implicit none
 
  type :: derived_t
     integer :: x
   contains
     procedure, pass(this) :: bar     
  end type derived_t
 
contains
 
  subroutine foo(x, y)
    integer, intent(in) :: x
    integer, intent(inout) :: y
    real(kind=rp) :: value
 
    do i = 1, 10
       ...
    end do
 
    if (x .lt. y) then
       ...
    end if
    
  end subroutine foo
  
end module example

Please note that the maximum line length in Neko should not exceed 80 columns.

Additionally the findent tool can be used to enforce these rules by assigning the following options. The documentation of findent provide details for emacs, vim and gedit. For VSCode, the Modern Fortran extension provide an integration.

findent -i2 -d3 -f3 -s3 -w3 -t3 -j3 -k- -Rr -c3 < input.f90 > formatted.f90

Data types

For portability reasons, it is essential to only use data type kinds defined in num_types.f90 and avoid legacy constructs like real*8 or integer(kind=8)

Floating-point numbers should be declared using real with the kind rp, which is the configured working precision for Neko (defaults to double). If single, double or quad precision is explicitly needed, use the kinds sp, dp or qp, respectively. For 16, 32, or 64-bit integers, Neko has defined the kinds i2, i4 or i8, respectively; however, for standard integers, it is perfectly fine to use a plain integer.

Table of Contents

Data types