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MathGroup Archive 1999

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Re: Options for a function

  • To: mathgroup at smc.vnet.net
  • Subject: [mg18128] Re: Options for a function
  • From: paulh at wolfram.com (P.J. Hinton)
  • Date: Fri, 18 Jun 1999 00:51:36 -0400
  • Organization: Wolfram Research, Inc.
  • References: <7ka6ub$ins@smc.vnet.net>
  • Sender: owner-wri-mathgroup at wolfram.com

In article <7ka6ub$ins at smc.vnet.net>, Virgil Stokes <virgil.stokes at neuro.ki.se> writes:

> The following simple function for testing
> options does not work the way I expect
> (Vers. 3.0.1).
> 
> 
> Options[g] = {Opt1->BoxCar};
> g[n_,opts___?OptionQ] :=
>    Module[{opt1,ans},
>   opt1 = Opt1 /. {opts} /. Options[g];
>   If[opt1 == BoxCar, ans = yes, ans = no];
>   {n,ans,opt1}
>  ];
> 
> If I use
> 
>   g[3]
> 
> then it returns
> 
> {3,yes,BoxCar}
> 
> which is of course correct. However, if I use
> 
> g[3,Opt1->TEST]
> 
> then it returns
> 
> {3,ans$7,TEST}
> 
> And, this is not what I would expect. In fact, I am
> unable to get the
> 
>    ans = no
> 
> part of the If statement to execute. Why?

Try using SameQ[] rather than Equal[] as the test in the If[] 
statement.

Here is what your function is doing.  Equal[] does not consider
this to be either True or False.

In[1]:= TEST == BoxCar

Out[1]= TEST == BoxCar

SameQ[] will give you the False result.

In[2]:= TEST === BoxCar

Out[2]= False

--
P.J. Hinton	
Mathematica Programming Group		paulh at wolfram.com
Wolfram Research, Inc.
Disclaimer: Opinions expressed herein are those of the author alone.


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