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Re: Optional Alternatives

• To: mathgroup at smc.vnet.net
• Subject: [mg50018] Re: Optional Alternatives
• From: Jens-Peer Kuska <kuska at informatik.uni-leipzig.de>
• Date: Thu, 12 Aug 2004 05:43:23 -0400 (EDT)
• Organization: Universitaet Leipzig
• References: <200408101002.GAA19525@smc.vnet.net> <cfcqsn$45f$1@smc.vnet.net>
• Reply-to: kuska at informatik.uni-leipzig.de
• Sender: owner-wri-mathgroup at wolfram.com

Hi,

f[Optional[x : (_Real | _Rational), 0.0]] := {Head[x], x}

??

Regards
  Jens

Selwyn Hollis wrote:
> 
> Is it possible to require a function argument to match alternative
> patterns and be optional at the same time? As a toy example, suppose I
> define
> 
>     f[x:_Real|_Rational]:= x
> 
> Is there a way make the argument optional with a given default value,
> say 0? I've tried this:
> 
>     f[Optional[x:_Real|_Rational, 0]]:= x
> 
> and various other combinations with no success. (Of course I could do
> this: f[]:= 0, but I'm interested in the more general issue.)
> 
> -----
> Selwyn Hollis
> http://www.appliedsymbols.com
> (edit reply-to to reply)

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