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MathGroup Archive 1998

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Re: help with Mathematica 3.0 'features' under NT


  • To: mathgroup@smc.vnet.net
  • Subject: [mg10788] Re: help with Mathematica 3.0 'features' under NT
  • From: Paul Abbott <paul@physics.uwa.edu.au>
  • Date: Thu, 5 Feb 1998 00:58:32 -0500
  • Organization: University of Western Australia
  • References: <6b3rkc$s0l@smc.vnet.net>

calvitti@gulam.ces.cwru.edu wrote:

> 2) Is there an elegant way for a default (or optional) argument to a
> function to take a value which depends on another argument to the same
> function if it's not explicitly passed? e.g. in "foo" I would like to
> have "a" default to Length[lst].
> 
>   foo[lst_List, a_Integer : Length[lst_]] := lst[[a]]
> 
> but foo[{5,6,7,8}] returns "List", which implies that it's defaulting
> "a" to 0. 

How about the following?

In[1]:= foo[lst_List, a_Integer] := lst[[a]] In[2]:= foo[lst_List] :=
lst[[Length[lst]]] In[3]:= foo[{5,6,7,8}]
Out[3]= 8

Cheers,
	Paul 

____________________________________________________________________ 
Paul Abbott                                   Phone: +61-8-9380-2734
Department of Physics                           Fax: +61-8-9380-1014
The University of Western Australia            Nedlands WA  6907       
mailto:paul@physics.uwa.edu.au  AUSTRALIA                            
http://www.pd.uwa.edu.au/~paul

            God IS a weakly left-handed dice player
____________________________________________________________________



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