Issue with package "pretty"

[Duncan Coutts]

On Sun, 2008-04-27 at 23:49 +0400, Bulat Ziganshin wrote:
> Hello Duncan,
> 
> Sunday, April 27, 2008, 11:42:01 PM, you wrote:
> 
> >> > The problem is that if you install pretty, Cabal will suddenly cease
> >> > working until you recompile it. It depends on a version of pretty
> >> > which gets bundled with GHC is purportedly of the same version as the
> >> > one on hackage, but the two aren't binary compatible. So when it tries
> >> > to use it, everything goes boom.
> 
> > The solution is not to identify installed packages by their name and
> > version but by a hash that identifies the package ABI.
> 
> probably not ABI (it should be the same), but random number generated
> when compilation (build) occurs

The package name and version do not identify an ABI. You change the ABI
by using -O0 vs -O1.

Also, I think modeling build processes as randomness isn't the right
approach. Build are really pure functions but with a rather large number
of inputs. The Nix approach is to identify them all and calculate a hash
of them all and use that to identify each built package.

Duncan