Re: Optional Alternatives
- To: mathgroup at smc.vnet.net
- Subject: [mg50047] Re: [mg50010] Optional Alternatives
- From: Bob Hanlon <hanlonr at cox.net>
- Date: Fri, 13 Aug 2004 05:55:40 -0400 (EDT)
- Reply-to: hanlonr at cox.net
- Sender: owner-wri-mathgroup at wolfram.com
The default value must be consistent with your Condition, that is, its Head
must be Real or Rational
Clear[f];
f[Optional[x:_Real|_Rational,0.]]:=x
f[]
0.
f/@{2,2.,1/2,x}
{f[2], 2., 1/2, f[x]}
Bob Hanlon
>
> From: Selwyn Hollis <sh2.7183 at misspelled.erthlink.net>
To: mathgroup at smc.vnet.net
> Date: 2004/08/11 Wed AM 05:53:08 EDT
> To: mathgroup at smc.vnet.net
> Subject: [mg50047] [mg50010] Optional Alternatives
>
> 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)
>
>