View source for HaskellImplementorsWorkshop/2012/Schuster

=Making cabal-install non-destructive=

''Philipp Schuster (speaker), Andres Löh''


Recently there have been more and more complaints about "cabal
dependency hell". Many of these complaints have their root in one
limitation: It is not possible to have more than one instance of a
certain package version installed per package database. Installing
another instance overwrites the existing instance and often breaks
other installed packages that depended on the overwritten instance.

During a Summer of Code project we are lifting this restriction by
making several instances of the same package version install next to
each other. This requires serious changes to ghc-pkg, cabal-install,
the Cabal library and their interaction. Specifically we need:

* A unique install location for each instance
* An improved way to uniquely identify packages
* A refined adhoc resolution method for GHC
* A few changes to the cabal-install solver
* A garbage collection mechanism for unused packages

In this talk, we are going to describe the changes as well as the
improvements possible for the end user. In addition to removing the
possibility of breaking installed packages, the new system also
promises much more fine-grained dependency tracking.

The project is a work in progress, and the talk will be a status
report.


[[Category:Community]]