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MathGroup Archive 2002

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Re: Holding Arguments in a Second Argument List

  • To: mathgroup at smc.vnet.net
  • Subject: [mg32259] Re: [mg32238] Holding Arguments in a Second Argument List
  • From: Andrzej Kozlowski <andrzej at tuins.ac.jp>
  • Date: Wed, 9 Jan 2002 23:37:14 -0500 (EST)
  • Sender: owner-wri-mathgroup at wolfram.com

I can't see a way to do what you want in the first part of your message 
(assign attributes for sub-arguments) but as for the second one way that 
will work is:


In[1]:=
foo[mathgroup_] :=
   Function[mat,
     Module[{},
         Do[If[Not[mathgroup === great], Return[$Failed]],{1}]
       ],
         {HoldFirst}]

e.g.

In[2]:=
foo[x][mat]

Out[2]=
$Failed

Andrzej Kozlowski
Toyama International University
JAPAN
http://platon.c.u-tokyo.ac.jp/andrzej/

On Wednesday, January 9, 2002, at 05:17  PM, David Park wrote:

> Dear MathGroup,
>
> I have a series of procedures which manipulate a matrix. I like to 
> define
> them in this fashion.
>
> function[args___][matrix_] := ... because then I can write lines like
>
> matrix // function[args...] etc.
>
> But I have to define the function so that matrix is held, and I don't 
> want
> to write Unevaluated with every use. But Attributes = {HoldFirst} only
> applies to the first argument list. Is there a direct way to define the
> attributes of a second argument list?
>
> In any case, I write the routines this way.
>
> function[args___]:=
> 	Function[matrix,
> 		Module[{}, code],
> 		{HoldFirst}]
>
> and that works. The code usually changes the matrix and I display it
> separately. But sometimes the operation will fail and then I would like
>
> function[args...][matrix]
>
> to return $Failed. But I am unable to do that. The best I seem to be 
> able to
> do is return Return[$Failed].
>
> Here is a sample routine which just tries to return $Failed.
>
> foo[mathgroup_] :=
>   Function[mat,
>     Module[{},
>         If[Not[mathgroup === great], Return[$Failed]]],
>     {HoldFirst}]
>
> foo[x][mat]
> Return[$Failed]
>
> Can anyone tell me how to get rid of the Return wrapper?
>
> Thanks
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>
>
>



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