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Re: Pattern Syntax for Alternate Heads with Default Value

• To: mathgroup at smc.vnet.net
• Subject: [mg125869] Re: Pattern Syntax for Alternate Heads with Default Value
• From: Yi Wang <tririverwangyi at gmail.com>
• Date: Thu, 5 Apr 2012 05:53:44 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com
• References: <jlh0n6$t6m$1@smc.vnet.net>

Hi, Ben,

Hope I understood your demand correctly. Try:

f[x : (_Real | _Integer) : 2.5] := x^2;

f[3] (* 9 *)
f[1.5] (* 2.25 *)
f[] (* 6.25 *)
f["hello"] (* f[hello] *)
f[Sin[x]] (* f[Sin[x]] *)

Cheers,
Yi

On Wednesday, April 4, 2012 4:28:22 AM UTC-4, Ben wrote:
> I'm trying to build a unary function which accepts only arguments with
> two possible heads and has a default value.  That is, something like
> the following, except that this doesn't work.  Anyone know how to do
> this correctly?
> 
> f[(x_Real | x_Integer) : 2.5] := x^2;
> where f[3] = 9
> and f[1.5] = 2.25
> and f[] = 6.25