Passing optional parameters through a wrapper routine

[bowman(at)null.edu (Kenneth P. Bowman)]

The _EXTRA keyword handles passing keyword parameters through a wrapper
routine, but what about optional parameters?  If my wrapper for TVRD has
one of my own (mandatory) parameters, do I have to do the following?

PRO TVRD_WRAPPER, my_arg, x0, y0, nx, ny, channel, _EXTRA = tvrd_keywords

CASE N_PARAMS() OF
   1 : image = TVRD(                         _EXTRA = tvrd_keywords)
   2 : image = TVRD(x0,                      _EXTRA = tvrd_keywords)
   3 : image = TVRD(x0, y0,                  _EXTRA = tvrd_keywords)
   4 : image = TVRD(x0, y0, nx,              _EXTRA = tvrd_keywords)
   5 : image = TVRD(x0, y0, nx,              _EXTRA = tvrd_keywords)
   6 : image = TVRD(x0, y0, nx, ny, channel, _EXTRA = tvrd_keywords)
   ELSE : MESSAGE, 'Incorrect number of arguments.'
ENDCASE
...

If I just try to pass undefined arguments through my wrapper, I get
'undefined variable' errors.  (Is TVRD just counting the number of passed
parameters and not checking to see if they are defined?)

Ken

-- 
Dr. Kenneth P. Bowman, Professor                409-862-4060
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Texas A&M University                            bowmanATcsrp.tamu.edu
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