On Wed, Dec 5, 2012 at 10:52 AM, Ivan Perez <ivanperezdoming...@gmail.com>wrote:
> Hello everyone, > > I've spent the last couple of days fighting my way around a dependency > hell with my own libraries and packages. > > If I install them package by package (by hand), I'm very likely to hit > one of these conflicts that I'm talking about. A simple example of > something that did happen: > - Package A depends on bytestring, and is compatible with both 0.9.* and > 0.10.* > - Package B depends on ghc, which I installed using the package > manager and which depends on bytestring 0.9.2 > - Package B depends on package A. > > I do not want to add to the cabal files that B depends on bytestring > 0.9.*, because it's not true, or that A depends on bytstring 0.9, > because it's also not true. > > I would like to the best approach to 1) avoid these situations and 2) > fix them when they happen. > > Regarding (2), Is there any way to automatically rebuild all the > broken packages? > Regarding (1), I thought about using cabal-dev, but I think I'll just > have the same problem, won't I? After all, I started from a clean > fresh ghc installation and I just installed what I needed to make my > program run. > Let's say you are working in a directory foo that contains a cabal file for package foo. When you type 'cabal-dev install', cabal-dev looks at foo.cabal in the current directory, it uses it to calculate constraints and then installs the dependencies locally that satisfy those constraints. It also has an install-deps command if you just want to install the deps but not build/install foo. Additionally, if you want to use locally modified versions of the dependencies use 'cabal add-source <path to dep>' from the foo directory to add your locally modified package to foo's index so that subsequent cabal-dev operations can find it and install it. Basically, don't install the deps by hand. Let cabal-dev figure out the mutually compatible versions and install that *locally* to where you're building foo. As for the problem of recursively rebuilding the deps, I think 'cab' [1] solves this but I haven't tried it. [1] http://hackage.haskell.org/package/cab > I also thought about adding process, bytestring and other global > packages to the list of constraints in ~/.cabal/config. Would this be > a good approach, or will it lead to bigger headaches in the future > (for instance, in the form of programs that just cannot be installed > at all)? > Adding these constraints will come back to bite you. That's been my experience. > > Also, is there any way to detect potential dependency hells without > having to install a package? (Some tool that will analyse the > dependency information (statically) and determine more strict or > incorrect upper and lower bounds for the dependencies of a package.) > --dry-run? Jason
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