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Package dependencies

• To: mathgroup at smc.vnet.net
• Subject: [mg45688] Package dependencies
• From: Maxim <dontsendhere@.>
• Date: Tue, 20 Jan 2004 05:07:59 -0500 (EST)
• Sender: owner-wri-mathgroup at wolfram.com

Suppose we have a package a.m defining function f:

BeginPackage["a`"]
f[0] = 0
EndPackage[]

Then we create package b.m which introduces additional definitions for
f:

BeginPackage["b`","a`"]
f[1] = f[0] + 1
EndPackage[]

Now after loading b.m we'll have f[0]=0 and f[1]=1. Finally, we want to
create a package c.m that determines when b.m should be autoloaded. We
add the following line to c.m:

DeclarePackage["b`","f"]

Unfortunately, it doesn't work that way:

In[1]:=
<<c`
f[1]

Out[2]=
1+f[0]

(standalone kernel will also give f::shdw warning). The reason is that
DeclarePackage creates symbol f (with attribute Stub) in the b` context.
This implementation decision seems rather questionable: the idea of
DeclarePackage is to load b.m when f is first used, which is exactly
what we want here -- but nobody said the symbol f was needed in context
b`!

Probably this difficulty can be avoided by some creative usage of Remove
and $NewSymbol, but simply adding Remove["b`f"] to b.m won't solve the
problem completely.

This is exactly the situation with Geometry\Polytopes.m,
Graphics\Polyhedra.m and Graphics\Kernel\init.m -- you can use
<<graphics` to declare most of the symbols in all the Graphics\*
packages, but not Tetrahedron, Cube and others because there are
definitions for them both in Polytopes.m and Polyhedra.m.

Maxim Rytin
m.r at prontomail.com