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MathGroup Archive 2005

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Re: "meta-programming" ?

  • To: mathgroup at smc.vnet.net
  • Subject: [mg60928] Re: [mg60908] "meta-programming" ?
  • From: "Christoph Lhotka" <lhotka at astro.univie.ac.at>
  • Date: Tue, 4 Oct 2005 01:24:56 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

On Mon, 3 Oct 2005 04:06:06 -0400 (EDT)
 Jack Goldberg <jackgoldberg at comcast.net> wrote:
> Hello once again,
> 
> I tend to use a lot of Modules in my programming style.  Here is a  
> model example:
> 
>       myfunction[   ] := Module[ {L1, L2, L3},
>          L1 =  some computations;
>          L2 =  more computations;
>          L3 =  more computations;
>                  final touches
>                              ]
> 
> When it comes time to check special (extreme) cases I use the simple  
> scheme of sequencially commenting out lines to see what has  
> happened.  In the next example I comment out lines  L3 to LN  (here  
> L3 is the last  labeled line).
> 
>       myfunction[ f__  ] := Module[ {L1, L2, L3},
>          L1 =  some computations;
>          L2 =  more computations (*;
>          L3 =  more computations;
>                  final touches *)
>                              ]
> 
> If the output is what I expect, I comment out  L3, etc.  So, in  
> short, if there are 10 lines of code in my module, I start with line  
> L1 and proceed to L10.  When every line does as expected, I try the  
> function on still another special case.
> 
> Now my question.  Can a "meta" program be constructed which does this  
> automatically?  Specifically, this metaprogram takes the input is     
> myfunction  and a specific input  f  to myfunction. The metaprogram  
> returns the output of each line of the module evaluated for the  
> specific input   f  to myfunction thus saving me the bother of  
> commenting out each line, one at a time for each extreme input to   
> myfunction.  (An extreme input might be an empty sum or a sum with  
> just one term, to take two easy examples.  Of course, this kind of  
> thing happens when myfunction  is deeply embedded in other code.)
> 
> Obviously, I am reluctant to use Trace or any of its variations.  But  
> perhaps some version of Trace is the way to go.  Well, at the very  
> least I can stick to the old fashion way, "one line at a time".
> 
> Jack
> 


My solution to this problem was to define a global debug variable $D and to
define my function like this:


function[args__]:=Module[{vars},
$D={
command1,
command2,
...
}[[-1]]
]

so I was able to see what happens inside the function by accessing $D.

In[..]:=$D

hope it helps



-- Mag. Christoph Lhotka --
University of Vienna / Institute for Astronomy
mail. lhotka at astro.univie.ac.at


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