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Optional Alternatives

• To: mathgroup at smc.vnet.net
• Subject: [mg50010] Optional Alternatives
• From: Selwyn Hollis <sh2.7183 at misspelled.erthlink.net>
• Date: Wed, 11 Aug 2004 05:53:08 -0400 (EDT)
• References: <200408101002.GAA19525@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

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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    • From: DrBob <drbob@bigfoot.com>
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    • From: Andrzej Kozlowski <akoz@mimuw.edu.pl>

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    • From: "Steven M. Christensen" <steve@smc.vnet.net>