On 25/02/2014 06:44, Michael Snoyman wrote:
Next is the issue of PVP. I am someone who has stopped religiously following the PVP in the past few years. Your email seems to imply that only those following the PVP care about making sure that "packages work together." I disagree here; I don't use the PVP specifically because I care about package interoperability.
The point of the PVP is to ensure that code builds. It's a purely compile-time concept. The PVP solves the problem of an update to a dependency causing a downstream package to break. And assuming everyone adheres to it[1], it ensures that cabal will never try to perform a build which isn't guaranteed to work.
But that's only one half of the "package interoperability" issue. I face this first hand on a daily basis with my Stackage maintenance. I spend far more time reporting issues of restrictive upper bounds than I do with broken builds from upstream changes. So I look at this as purely a game of statistics: are you more likely to have code break because version 1.2 of text changes the type of the map function and you didn't have an upper bound, or because two dependencies of yours have *conflicting* versions bounds on a package like aeson[2]? In my experience, the latter occurs far more often than the former.
It's worth mentioning that cabal failing to find a solution is far less costly for me to discover than cabal finding a solution and then having a build of a large graph of packages fail, because by that point I've wasted a lot of time waiting for the build and I now have a thoroughly confused package database to recover from (whether using a sandbox or not). Ganesh