Re: package frenzy

Joris Bleys wrote: 
Hello all!

I'm experiencing some problems using packages in Lisp and I'm wondering what your opinions are about the packages-facility in Lisp. I've been hearing around and most of my comrades suggest not to use packages. I'd like to use them to avoid nasty things like name-clashes (that's what they're for, right?). Is there any guide on how packages should be used? 

No, you absolutely should use packages.  Programming in the CL-USER
package means your code cannot be integrated with others who do the
same, and is possibly nonportable anyway since implementations can
stick any symbols they want in that package.

I typically make the packages fairly large, and put their definitions
off in their own files, but this is style.

It's a good idea to avoid using the :: package prefixes when possible.
That's a sign that someone is cheating and going behind the back
of a package's public interface.


Let's say I have some package :exporting-package, which has two functions: ep-internal-fn and ep-external-fn. The ep-internal-fn gets a string as argument and returns a symbol using (read-line str NIL NIL). The ep-external-fn uses eq to compare the result of ep-internal-fn with a pre-programmed symbol 'TEST. The ep-external-fn is exported.

Now another package is defined :importing-package which uses the :exporting-package (use-package). When ep-external-fn is called, the equality is always false. This happens because the result of ep-external-fn is a symbol in the package :importing-package, whereas the 'TEST symbol is defined in the :exporting-package. 

That symbol was part of the API of the exported function, so it itself
should have been exported also.  Or, you could have used a keyword
symbol.

(Also be careful when calling READ-LINE that you've bound *PACKAGE*
appropriately.)

	Paul
.

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