Introduction :

In Modern Fortran , program is separated to a structure that have a main file and connect with multi-library , that have Module structure. This new feature is so powerful and improve development standard better before.

In this picture , Main program is using 3 library module called : Module_1, Module_2, Module_3 , and only Module_1 and Module_2 is need to import directly to Main program . The green arrow mean “import” or “USE syntax” in this picture.

How Module Structure look like !

Under code block , the module name is written after MODULE syntax and END MODULE syntax , and called “stla_io” in this example . Later, this module name can be used to import to main file or other module file using USE syntax.

MODULE stla_io
     ----------------------- something ------------
END MODULE stla_io

Next to module name , we will have space for define some new feature of modern fortran :

• USE syntax : import external library or other module to use some external function

MODULE stla_io
     USE :: somelib , only : somefunction 
     implicit none

     ----------------------- something ------------
END MODULE stla_io

• PARAMETER , SAVE variables : we will need this sometime for mathematic

MODULE stla_io

      USE :: somelib , only : somefunction 
      implicit none

      INTEGER, PARAMETER     :: some_parameter
      INTEGER, SAVE          :: some_save_variable 
      ------  PARAMETER or SAVE variables -----

     ----------------------- something ------------
END MODULE stla_io

• TYPE syntax : of course , Modern Fortran is object-oriented languages , define some object like monster or player for your 2d games here

 MODULE stla_io

      USE :: somelib , only : somefunction 
      implicit none

      ------  PARAMETER or SAVE variables -----

      TYPE :: Object_type
         ---- OBJECT DEFINE ----
      END TYPE Object_type


     ----------------------- something ------------
END MODULE stla_io

• INTERFACE syntax : it have 2 purpose, one is for create a interface for other language functions like as C\C++ , winapi . We only need C library header file for compile process, and setup linker for these library later when compile with main file in last process . Second is for define generic name for functions that have multi-version. In general , all multi-version functions need be place after CONTAINS syntax in module file.

MODULE stla_io

      USE :: somelib , only : somefunction 
      implicit none

      ------  PARAMETER or SAVE variables -----
      ------- OBJECT DEFINE ----------
  

      INTEFACE  
          --- EXTERNAL C/C++ FUNCTION INTERFACE----
      END INTERFACE 

      INTEFACE generic_name 
          --- GENERIC SUBROUTINE ----
      END INTERFACE 

     ----------------------- something ------------
END MODULE stla_io

• CONTAINS syntax : the traditional subroutines and functions define will be place after breakline of this syntax . We can use INCLUDE syntax to import all old library file to this CONTAINS block, but rewrite to new standard may be better.

MODULE stla_io

      USE :: somelib , only : somefunction 
      implicit none

      ------  PARAMETER or SAVE variables -----
      ------- OBJECT DEFINE ----------
      ------- EXTERNAL C/C++ FUNCTION INTERFACE ----
      ------- GENERIC SUBROUTINE INTERFACE ----

      CONTAINS
     -------- SUBROUTINE, FUNCTION DIFINE ------------
END MODULE stla_io

After all, combine all upper things , we have module file look like under code :

MODULE stla_io

      USE :: somelib , only : somefunction 
      implicit none

      INTEGER, PARAMETER     :: some_parameter
      INTEGER, SAVE          :: some_save_variable 
      ------  PARAMETER or SAVE variables -----

      TYPE :: Object_type
         ---- OBJECT DEFINE ----
      END TYPE Object_type

      INTEFACE  
          --- EXTERNAL C/C++ FUNCTION INTERFACE----
      END INTERFACE 

      INTEFACE  generic_name 
          --- GENERIC SUBROUTINE ----
      END INTERFACE 

      CONTAINS
          ------- old-fortran-lib-if-want-to-include ---
          INCLUDE ".\old_subroutine_fortran_file.f90" 

          subroutine subroutine_of_this_module
            ------- subroutine define ----
          end subroutine 
    
END MODULE stla_io