Re: Cabal vs Haskell [sic]

On Tue, 26 Apr 2005, Shae Matijs Erisson wrote:

"S. Alexander Jacobson" writes:

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4. A set of modules may be dependent on a set of packages if and only if that set of packages is the only set of packages that may contain them.

I don't understand. What does this mean? Modules must be contained by a package to depend on that package?

Package P contains module A. Module A only imports module B. So module A is dependent on itself and access to module B. Package P does not contain a module B, but its build depends tag does identify a set of pacages on which it depends Ps Access to module B is dependent on access to Ps if and only if no other package provides access to module B. The spec says that build-depends identifies the packages "needed to build this one." If packages other than Ps may provide access to module B then the build-depends tag cannot identify the dependencies of module A because Ps are not necessary, only sufficient. Build-depends identifies necessity not sufficiency.

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5. Since more than one set of packages may contain the same set of modules, the current Haskell story cannot be consistent with the current Cabal story.

Why can't multiple packages have the same set of modules?

Exactly! This all started because I had claimed that the Haskell story is that module names identify modules and that the Cabal story is that package names qualify module names to identify modules. If module names fully identify modules then multiple packages may expose the same set of modules. However, if package names qualify module names then, by definition, a module in a different package is a differnt module. I favored the Haskell story, in part, because I believe that multiple packages should be allowed to have the same set of modules. Isaac and Simon Marlow, however denied my interpretation of Cabal. However, this proof shows that Cabal's build-depends doesn't make sense unless only one package may expose a given module and that would be true if and only if package names qualify module names. And, if Cabal requires that package names qualify module names, it is inconsistent with the Haskell story that they don't! -Alex- ______________________________________________________________ S. Alexander Jacobson tel:917-770-6565 http://alexjacobson.com