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Re: Pattern Syntax for Alternate Heads with Default Value

• To: mathgroup at smc.vnet.net
• Subject: [mg125901] Re: Pattern Syntax for Alternate Heads with Default Value
• From: Murray Eisenberg <murray at math.umass.edu>
• Date: Fri, 6 Apr 2012 05:57:44 -0400 (EDT)
• Delivered-to: l-mathgroup@mail-archive0.wolfram.com

While mathematically each integer is a real number, a Mathematica object 
with head Integer does _not_ have head Real. Thus:

   g[x_Real] := x^2
   g[3]
g[3]


On 4/5/12 5:51 AM, Murta wrote:
> On Apr 4, 5:28 am, Ben<ben... at gmail.com>  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
>
> Hi Ben
> Maybe something like that?
>
> f[x_ (Real | Integer)] := x^2; f[] = 6.25;
>
> (But all Integer are Real, I don't understand the application.
> It could be f[x_Real: 2.5] := x^2)
> best regards
> Murta
>

-- 
Murray Eisenberg                     murray at math.umass.edu
Mathematics & Statistics Dept.
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University of Massachusetts                413 545-2859 (W)
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