functions as arguments ?

[Udo Grabowski <udo.grabowski(at)imk.fzk.de>]

Hello, 

I'm looking for a way to do something like the Fortran construct

 program test
    call proc (func1)
    call proc (func2)
 end
	subroutine proc(func)
            call func
        end

where func1,2 are given external functions defined somewhere.
Functional arguments are seemingly not possible in IDL, but I found
a preliminary and ugly solution with a wrapper class:
;=================================================
;----------------------------------------------;
; functions finally to be called alternatively ;
;----------------------------------------------;
function func1, n
   return, n+1
end
function func2, n
   return, n+2
end
;----------------------------;
; wrapper class for function ;
;----------------------------;
pro FUNC__define
  struct = { FUNC, i:0 }  ;;; (i is dummy)
  return
end

function FUNC::init
   return, 1
end
;-------------------------------------------;
; UGLY solution:                            ;
; method which calls the hardwired function ;
;-------------------------------------------;
function FUNC::transform, n
   m = func2(n)
   return,m    
end
;--------------------------------------------;
; function f gets its proc from main program ;
;--------------------------------------------;
function f, n, proc=proc
    n = proc -> transform(n)
    return, n
end
;------------------------------------------------;
; main program calls f with functional argument, ;
; but cannot change it dynamically               ;
;------------------------------------------------;
pro call_functions

  func_obj = OBJ_NEW('FUNC')

  n = 1
  s = f(n,proc=func_obj)

  print,'n=',n

; any possibility to do anything like:  ???
;  func_obj -> SetFunction (func1)  
;  s = f(n,proc=func_obj)
;  print,'n=',n

end
;=================================================
This solution is not flexible because I need another
wrapper class if I additionally want to call func1.
I also considered pointers, but all these concepts
seem to be applicable to data structures only. Is
there a more elegant solution to that problem ?
--  
Dr. Udo Grabowski                           email: udo.grabowski@imk.fzk.de
Institut f. Meteorologie und Klimaforschung II, Forschungszentrum Karslruhe
Postfach 3640, D-76021 Karlsruhe, Germany           Tel: (+49) 7247 82-6026
http://www.fzk.de/imk/imk2/ame/grabowski/           Fax:         "    -6141