Re: Optional
- To: mathgroup at smc.vnet.net
- Subject: [mg33700] Re: Optional
- From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
- Date: Tue, 9 Apr 2002 01:02:05 -0400 (EDT)
- Organization: Universitaet Leipzig
- References: <a8m3i8$obr$1@smc.vnet.net>
- Reply-to: kuska at informatik.uni-leipzig.de
- Sender: owner-wri-mathgroup at wolfram.com
Hi,
why not use
f[]={1}
f[index : {_Integer ...}] := index
Ben Langton wrote:
>
> Hi all,
>
> I am having a problem with the Optional function which I have reduced to the
> following snippet of code :
>
> f // Clear;
> f[Optional[index : {_Integer ...}, {1}]] := index;
> f[]
>
> My understanding of the Optional command is that the function f should
> accept a list of zero or more integers as its argument or, if that is
> missing, use the default value of {1}.
>
> Under version 3, f[] (f with no arguments) returns {1}, as I would expect,
> yet under version 4.1 it returns the function evaluated.
Sequence[] can't match the first pattern {_Integer...} and so the
optional argument is never used.
Regards
Jens