Re: passing functions as arguments in IDL?

[Martin Schultz <martin.schultz(at)dkrz.de>]

Benno Puetz wrote:
> 
> David Fanning wrote:
> 
> > Rick Baer (baer@hpl.hp.com) writes:
> >
> > >  Is there any way to pass functions as arguments in IDL? I would
> > > like to be able to do something like this:
> > >...
> > > IDL> print, tf1, f1, 4
> >
> > You can do this:
> >
> >  function f1, x
> >     return, x*x
> >  end
> >
> >  function tf1, func, arg
> >    IF Size(func, /Type) NE 7 THEN BEGIN
> >         Print, 'String argument required'
> >        RETURN, -1
> >    ENDIF
> >     retVal = Call_Function(func, arg)
> >    return, retVal
> >  end
> >
> >    IDL> print, tf1('f1', 4)
> >
> > Cheers,
> >
> > David
> > --
> 
> Would it also be possible to pass argument lists of variable length,
> depending on the function to be called?
> 
> I've tried the _EXTRA keyword but to no avail ...
> 

Only if you don't exceed the number of arguments the underlying function
can take
AND (in case you pass fewer than the maximum number of arguments) if the
function is
written well enough to cope with an incomplete set of arguments.

Please find attached a program named loop.pro which illustrates this.
Loop.pro is a
wrapper routine that allows to call functions which accept only scalars
with arrays
as first argument.

Good luck,
Martin


-- 
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
[[ Dr. Martin Schultz   Max-Planck-Institut fuer Meteorologie    [[
[[                      Bundesstr. 55, 20146 Hamburg             [[
[[                      phone: +49 40 41173-308                  [[
[[                      fax:   +49 40 41173-298                  [[
[[ martin.schultz@dkrz.de                                        [[
[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[[
; $Id: loop.pro,v 1.10 1999/01/22 20:12:17 mgs Stab $
;-------------------------------------------------------------
;+
; NAME:
;        LOOP
;
; PURPOSE:
;        This routine provides a wrapper for function calls that accept
;        only scalars so that they can operate on arrays.
;
; CATEGORY:
;        serious stuff
;
; CALLING SEQUENCE:
;        result = LOOP(name,arg,p1,p2,p3,p4)
;
; INPUTS:
;        NAME --> the name of the function (string)
;
;        ARG --> the argument (array)
;
;        P1 .. P4 --> optional function parameters 
;
; KEYWORD PARAMETERS:
;        unfortunately none. Would be nice if _EXTRA would work.
;
; OUTPUTS:
;        a result *vector* with the same number of elements as arg.
;
; SUBROUTINES:
;
; REQUIREMENTS:
;
; NOTES:
;
; EXAMPLE:
;        a=[0.05,0.01,0.001]
;        print,loop("chisqr_cvf",a,17)
; 
;        IDL prints:
;        27.5871      33.4087      40.7903
;
; MODIFICATION HISTORY:
;        mgs, 05 Dec 1997: VERSION 1.00
;
;-
; Copyright (C) 1997, Martin Schultz, Harvard University
; This software is provided as is without any warranty
; whatsoever. It may be freely used, copied or distributed
; for non-commercial purposes. This copyright notice must be
; kept with any copy of this software. If this software shall
; be used commercially or sold as part of a larger package,
; please contact the author to arrange payment.
; Bugs and comments should be directed to mgs@io.harvard.edu
; with subject "IDL routine loop"
;-------------------------------------------------------------


function loop,name,arg,p1,p2,p3,p4
 
 
   on_error,2   ; return to caller
 
 
   result = fltarr(n_elements(arg))
 
; print,n_elements(p1),n_elements(p2),n_elements(p3),n_elements(p4)
   ; call function with number of parameters supplied
   ; not very elegant but safe.
   ; (would probably look nicer with EXECUTE, but isn't that slower ?)
 
   if (n_elements(p4) gt 0) then begin
       for i=0,n_elements(arg)-1 do   $
           result(i) = call_function(name,arg(i),p1,p2,p3,p4)
       return,result
   endif
 
   if (n_elements(p3) gt 0) then begin
       for i=0,n_elements(arg)-1 do   $
           result(i) = call_function(name,arg(i),p1,p2,p3)
       return,result
   endif
 
   if (n_elements(p2) gt 0) then begin
       for i=0,n_elements(arg)-1 do   $
           result(i) = call_function(name,arg(i),p1,p2)
       return,result
   endif
 
   if (n_elements(p1) gt 0) then begin
       for i=0,n_elements(arg)-1 do   $
           result(i) = call_function(name,arg(i),p1)
       return,result
   endif
 
 
   for i=0,n_elements(arg)-1 do   $
       result(i) = call_function(name,arg(i))
   return,result
 
end