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MathGroup Archive 2005

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Re: usage messages in packages

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58097] Re: [mg58064] usage messages in packages
  • From: Andrzej Kozlowski <andrzej at akikoz.net>
  • Date: Sat, 18 Jun 2005 06:07:50 -0400 (EDT)
  • References: <NDBBJGNHKLMPLILOIPPOOEOBEIAA.djmp@earthlink.net>
  • Sender: owner-wri-mathgroup at wolfram.com

Very nice. Now if only someone could tell about this the authors of  
the Combinatorica package  ....

Andrzej Kozlowski

On 17 Jun 2005, at 23:04, David Park wrote:

>
> Andrzej,
>
> There is a method of appending to an existing usage message in a  
> package.
> Here is an example (from the Algebra`ExpressionManipulation`  
> package at my
> web site).
>
> $NewMessage[Extract, "usage"];
> Extract::usage =
>   Extract::usage <>
>     " The positions in Extract can be extended positions such as \n \
> eP[{1},{2,4}] which is the position of a+c in f[1+a+b+c]."
>
> Then when a user types ?Extract he gets...
>
> Extract[expr, list] extracts the part of expr at the position  
> specified by
> list. Extract[expr, {list1, list2, ... }] extracts a list of parts  
> of expr.
> Extract[expr, ... , h] extracts parts of expr, wrapping each of  
> them with
> head h before evaluation. The positions in Extract can be extended  
> positions
> such as eP[{1},{2,4}] which is the position of a+c in f[1+a+b+c].
>
> David Park
> djmp at earthlink.net
> http://home.earthlink.net/~djmp/
>
>
>
> From: Andrzej Kozlowski [mailto:andrzej at akikoz.net]
To: mathgroup at smc.vnet.net
>
>
> One aspect of Mathematica packages that seems to me to be poorly
> designed is the way package usage messages can cover up a built in
> usage messages without any warning. A particularly irritating
> instance of this is when a package overloads the definition of a
> built in functions so that user receives no information at all about
> what happened. As an example compare:
>
>
> ?Normal
>
> Normal[expr] converts expr to a normal expression, from a
> variety of special forms.
>
> load the Combinatorica package:
>
>
> <<discretemath`combinatorica`
>
>
> ?Normal
>
> Normal is a value that options VertexStyle, EdgeStyle, and \
> PlotRange can take on in ShowGraph.
>
> Another curious thing. Quit the Kernel and now try again loading the
> Combinatorica package in a different way
>
> In[1]:=
> <<discretemath`
>
> This time the usage message was not covered up:
>
> In[2]:=
> ?Normal
>
> Normal[expr] converts expr to a normal expression, from a \
> variety of special forms.
>
> I had never realised that one could load directories of packages by
> using only small letters as in the above example until I saw Maxim
> doing it. This also works:
>
> << discretemath`combinatorica`
>
>
> Actually, this is consistent with the documentation which says:
>
>
>       <<dir` , initialize all packages from directory dir,
>       <<dir`package` , read in a package from the named directory
>
> but I had always assumed that "dir" and "package" actually meant
> "Dir" and "Package".
>
>
> Andrzej Kozlowski
> Chiba, Japan
> http://www.akikoz.net/andrzej/index.html
> http://www.mimuw.edu.pl/~akoz/
>
>
>
>


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