On 10 May 2005 11:48, Tony Finch wrote:
On Tue, 10 May 2005, Simon Marlow wrote:
2. The GHC build could start using -fignore-all-packages to insulate itself from the environment (or, simpler but more hacky: -ignore-package lang). This isn't a *solution* as such, because the problem affects everyone, not just us.
I'm slightly surprised that this isn't already the default, and that probably explains the recent argument. In the C world the only libraries that matter to the build environment are the ones you explicitly pull in. Overlaps still matter but only within your program. On the other hand Perl's module namespace is global, and a (usually implicit) search path is used to resolve conflicts.
FWIW, I tend to agree. -fhide-all-packages should be the default. (I know that others disagree, though).
I greatly prefer the former model. Perl is a real pain if you want multiple parallel installations of slightly different versions of the same code - you effectively need a separate Perl installation for each installed version of a program that uses Perl.
Perhaps the missing idea is the package configuration step, during which its dependencies are resolved to installed libraries on the build machine and any conflicts are dealt with.
Actually this is what we're proposing to do in Cabal. Anyone using Cabal won't have to worry about these issues, but they will have to specify all package dependencies explicitly.
The package is shipped with abstract dependencies (module names and perhaps version numbers), but by the time the compiler gets involved these have been resolved to paths in the file system.
It's a bit higher level than that: the compiler does have an understanding of packages, but it just maps a package name to a library and a bunch of interface files. So essentially what you describe is the way it works (with Cabal, at least). Cheers, Simon