Dynamic function creation from another function

Question

I have a Fortran 90 subroutine which takes a function as an argument, and I would like to pass a modified version of that function into another subroutine. I want the progra

Answer 1

This is not so easy. In some languages you can pass pointers to nested functions in a so called closure. This is not possible in Fortran (or C and similar languages), because the data are destroyed with the stack of the higher function. I would suggest you to try function objects, i.e. a class with a function pointer (or more) and data needed for the function. In this way you can even do function composition and similar functional stuff.

More on the concept http://en.wikipedia.org/wiki/Function_object

Below is a sample for a function object for composition of two single argument functions:

module ComposeObj
  use Parameters, only: rp
  use AritmFunctions, only: fce
  implicit none

  private
  public Compose

  type Compose
    private
    procedure(fce),pointer,nopass :: f1 => null(),f2=>null()
  contains
    procedure,public :: call => helper
  end type Compose

  interface Compose
    procedure NewCompose
  end interface

 contains

  function NewCompose(f,g)
    procedure(fce) :: f,g
    type(Compose) :: NewCompose

    NewCompose%f1 => f
    NewCompose%f2 => g
  end function NewCompose

  pure real(rp) function helper(this,x)
    class(Compose),intent(in) :: this
    real(rp),intent(in) :: x
    helper = this%f1(this%f2(x))
  end function helper

end module ComposeObj

Answer 2

You could do a lot with procedure pointers, constructing a function that is a combination of other functions. See Function pointer arrays in Fortran for a code example.