program main
use, intrinsic :: iso_fortran_env, only : error_unit, sp=>real32, dp=>real64
implicit none

real(sp) :: a32
real(dp) :: a64

real(sp), parameter :: pi32 = 4*atan(1._sp)
real(dp), parameter :: pi64 = 4*atan(1._dp)

if (pi32 == pi64) error stop 'real32 values generally do not exactly equal real64 values'

call timestwo(a32)
call timestwo(a64)

contains

elemental subroutine timestwo(a)

class(*), intent(inout) :: a

select type (a)
  type is (real(sp))
    a = 2*a
  type is (real(dp))
    a = 2*a
  type is (integer)
    a = 2*a
  class default
    error stop 'requires real32, real64 or integer'
end select

end subroutine timestwo

end program