Procedure Pointers

In addition to being able to pass procedures as parameters since FORTRAN 77, Fortran 2003+ supports procedure pointers, allowing you to select one of a family of procedures with similar parameters

First, make some example functions

module ExampleFuncs
   implicit none
contains
function f1 (x)
  real :: f1
  real, intent (in) :: x
  f1 = 2.0 * x
end function f1
function f2 (x)
   real :: f2
   real, intent (in) :: x
   f2 = 3.0 * x**2
end function f2
end module ExampleFuncs

A simple program

program test_func_ptrs
use ExampleFuncs
implicit none
!! define an abstract template defining the family of procedures
abstract interface
  function func (z)
     real :: func
     real, intent (in) :: z
  end function func
end interface

!! define a pointer of the abstract type
procedure (func), pointer :: f_ptr => null ()

character(len=:),allocatable :: name
integer :: i

write (*, '( / "Input function name (f1|f2 ")', advance="no" )
read (*, *) name
select(name)
case('f1'); f_ptr => f1
case('f2'); f_ptr => f2
case default
   write(*,*)'bad function name, allowed names are "f1" and "f2"'
   stop
end select

do i=1,100
   write(*,*)'for ',i,'result is ',f_ptr (real(input))
enddo

end program test_func_ptrs