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MathGroup Archive 2005

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Re: usage messages in packages

  • To: mathgroup at smc.vnet.net
  • Subject: [mg58095] Re: [mg58064] usage messages in packages
  • From: "David Park" <djmp at earthlink.net>
  • Date: Sat, 18 Jun 2005 06:07:47 -0400 (EDT)
  • Sender: owner-wri-mathgroup at wolfram.com

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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