Run with

  /usr/bin/emacs -Q -l init.el bug.org

One should be able to click on the following link
- elisp:org-babel-tangle
to tangle (export) the code blocks in this org file.

Then one should be able to execute the code block
- [[code_block_to_execute]]
by using C-c C-c in code block.

However, it does not work because the tangle stage wraps the fortran
module in

  program main

  end program main

which prevents the code from compiling.



#+BEGIN_SRC fortran :tangle circle.f90
  MODULE Circle
        implicit None
        public :: area
  contains
        function area(r) 
        implicit none
        real, intent(in) :: r
        real :: area
        area = 3.14159 * r**2
        return
        end function area
  END MODULE Circle
#+END_SRC


#+BEGIN_SRC fortran :tangle main.f90
  program main

  use circle, only: area

  implicit none
  integer :: i
  REAL, DIMENSION(5) :: R
  R = (/1.0, 2.0, 3.0, 4.0, 5.0 /)

  print *, "#+tblname: circle-area"
  do i = 1, 5
     print *, "|", R(i), "|", area(R(i)), "|"
  end do

  end program main
#+END_SRC


#+BEGIN_SRC makefile :tangle makefile-main
  circle:
  	@gfortran -c circle.f90

  main: circle
  	@gfortran -c main.f90
  	@gfortran circle.o main.o -o main

  clean:
  	@rm -f *.o main
#+END_SRC

<<code_block_to_execute>>
#+BEGIN_SRC sh :results raw replace
  make -f makefile-main clean main
  ./main
#+END_SRC

#+RESULTS:
 #+tblname: circle-area
 |   1.00000000     |   3.14159012     |
 |   2.00000000     |   12.5663605     |
 |   3.00000000     |   28.2743111     |
 |   4.00000000     |   50.2654419     |
 |   5.00000000     |   78.5397491     |