Putting Fortran code in modules

[Beliavsky]

@Beliavsky

So to transform a Fortran code that is comprised of multiple source files to one in which procedures are in modules, one needs to

(1) put the code in each source file in a module. My convention is that a file foo.f90 contains module foo_mod.
(2) remove declarations of called functions in the caller, as shown above
(3) add the appropriate use foo_mod statement in the caller, for procedures invoked from other modules or the main program

(4) One also needs to remove EXTERNAL declarations from the code, since for example the code below will not compile if the commented out lines are reinstated:

module m
contains
function square(i) result(i2)
implicit none
integer, intent(in) :: i
integer             :: i2
i2 = i**2
end function square

function cube(i) result(i3)
implicit none
integer, intent(in) :: i
integer             :: i3
! external square
i3 = i * square(i)
end function cube
end module m

program main
use m
implicit none
! external cube
print*,cube(5)
end program main