On 18 May 2005 17:59, S. Alexander Jacobson wrote:
On Wed, 18 May 2005, Simon Marlow wrote:
On 17 May 2005 17:14, S. Alexander Jacobson wrote:
With SearchPath, you supply the URLs of the module maps you want to use. SearchPath then uses these map to locate, download and "install" needed libraries without further user intervention.
A module map is just a file mapping module names to the base URLs of directories in which they reside. If you want to supply the URL of a particular version of a module map rather than "latest" you are free to do that.
But how do you know what module maps were being used by the author of the module you download? Don't you have to download their module map file too?
The reality is that, no matter what, you always have to assume that the user and author of a particular module/package need to live in basically the same universe of modules and packages.
So in fact I *cannot* locally modify my module map to use a different version of an imported module. The module map is fixed and global, although I can extend it locally. So basically, there's no versioning, because everyone has to use the same version of everything. Right? Well, except that I can enter into a pact with another module author to use a certain version of a third party's module, and we both have to remember that we have the pact because the information doesn't travel with the module sources (unlike Cabal, where dependencies are explicit, I might add).
With Cabal, if you download two packages, how do you know that they won't require conflicting versions of another module/package?
As discussed before, the fact that you can't use two versions of a package simultaneously is a missing feature in the implementation, nothing more. Cheers, Simon