Re: keyword params in HISTOGRAM

[thompson(at)orpheus.nascom.nasa.gov (William Thompson)]

Mark Fardal wrote:
> 
> Hi,
> 
> I'm sure this is a stupid question, but I can't figure it out.
> Normally when you pass keyword parameters, you can pass something
> that's undefined, right?  As in this example
> 
	(rest deleted)

Although the example you give isn't optimal, it is correct that you can pass
undefined keywords to procedures.  This is because inside procedures you can
check to see if keywords are passed with either the N_ELEMENTS function or
KEYWORD_SET.  Thus, passing an undefined keyword is equivalent to not passing
it at all, which is a useful thing IMHO.  Unfortunately, this doesn't work with
built-in IDL routines, which I find a very inconvenient and silly restriction.

Bill Thompson