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)

**Follow-Ups**:**Re: Optional Alternatives***From:*DrBob <drbob@bigfoot.com>

**Re: Optional Alternatives***From:*Andrzej Kozlowski <akoz@mimuw.edu.pl>

**References**:**50,000th Message***From:*"Steven M. Christensen" <steve@smc.vnet.net>