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Re: Function in a package

• To: mathgroup at smc.vnet.net
• Subject: [mg42526] Re: [mg42493] Function in a package
• From: Dr Bob <drbob at bigfoot.com>
• Date: Sat, 12 Jul 2003 05:19:34 -0400 (EDT)
• References: <200307110657.CAA17172@smc.vnet.net>
• Sender: owner-wri-mathgroup at wolfram.com

First of all, you've written the test function as if, at all costs, you 
don't want anybody to understand what it does.  Here's a simpler function 
that MAY do the same thing.

test[dat_, opts___?OptionQ] :=
   Module[{n = norm /. Flatten@{opts, norm -> fst}},
    Which[
      n === fst, First[dat],
      n === max, Max[dat]
      ]
    ]

I say MAY, because a lot depends on whether you intended Global values of 
norm, fst, and max to have an effect on the outcome.  Probably one of those 
had a value when you ran your tests, and that accounts for the difference 
in outcomes.  It's generally bad form (counter to functional programming 
principles) to have a function depend on global variables.  It's not always 
a bad idea, but it's certainly a bad idea to do it without thinking about 
it.

Also, as you wrote the function (and me too), the 'norm' that you use in a 
call to the function is global, but the norm mentioned twice inside the 
function is a Private version of norm, so the function can't operate as you 
probably intend, even if norm doesn't have a Global value.  This could also 
explain the behavior you're seeing.

I have to leave you at this point, as I haven't learned all the mysteries 
of options in package functions myself!  I'll be interested to see other 
answers to this.

Bobby

On Fri, 11 Jul 2003 02:57:54 -0400 (EDT), Roger Mason 
<rmason at sparky2.esd.mun.ca> wrote:

> Hello,
>
> I have written and tested successfully a function in a notebook.  On
> putting the function in a package it ceases to work.
>
> Here is the package:
>
> BeginPackage["FredNoEDA`"]
>
> TestPkgNoEDA::usage = "a test function.";
>
> Begin["`Private`"]
>
> TestPkgNoEDA[dat_, opts___?OptionQ] := Module[
> {n, Tow, Tow0},
> n = norm /. Flatten[{opts}] /. {norm -> fst};
> Tow = dat;
> If[
> n == fst, Tow0 = First[Tow]
> ];
> If[
> n == max, Tow0 = Tow[[
> Position[Tow, Max[Tow] ][[1, 1]]
> ]]
> ];
> Tow0
> ]
>
> End[]
>
> Protect[TestPkgNoEDA]
>
> EndPackage[];
>
> Here is the identical function (under a different name) from a notebook:
>
> TestPkg[dat_, opts___?OptionQ] := Module[
> {n, Tow, Tow0},
> n = norm /. Flatten[{opts}] /. {norm -> fst};
> Tow = dat;
> If[
> n == fst, Tow0 = First[Tow]
> ];
> If[
> n == max, Tow0 = Tow[[
> Position[Tow, Max[Tow] ][[1, 1]]
> ]]
> ];
> Tow0
> ]
>
> Here are some test data:
>
> In[2]:=
> tst = Table[x, {x, 1, 10}]
>
> Out[2]=
> {1, 2, 3, 4, 5, 6, 7, 8, 9, 10}
>
> Here are the results of a test:
>
> Needs["FredNoEDA`"]
>
> In[6]:=
> TestPkgNoEDA[tst, norm -> max]
>
> Out[6]=
> 1
>
> In[11]:=
> TestPkg[tst, norm -> max]
>
> Out[11]=
> 10
>
> Can anyone explain why the version of the function in the package returns
> an incorrect result?
>
> Thanks,
> Roger Mason
>
>



-- 
majort at cox-internet.com
Bobby R. Treat

• References:
  • Function in a package
    • From: Roger Mason <rmason@sparky2.esd.mun.ca>