Upgrading packages/Updating to GHC 6.10

A list of things that need updating when porting packages to newer library/cabal versions.

Updating to GHC 6.8 and Cabal 1.2

Cabal API changes

Many packages that use non-default Setup.hs or Setup.lhs files need to be updated as they use Cabal APIs that have changed. In many cases new features in Cabal-1.2 allow these packages to go back to using the default Setup.hs.

A more detailed survey of the packages from the hackage collection is here: http://www.haskell.org/pipermail/libraries/2007-September/008265.html

base package split up

The base package was split up, and new dependencies are now required;

• array: Data.Array and below
• bytestring: Data.ByteString and below
• packedstring: Data.PackedString (deprecated)
• containers: Data.{Graph,IntMap,IntSet,Map,Sequence,Set,Tree}
• random: System.Random
• pretty: Text.PrettyPrint and below
• process: System.Cmd, System.Process and below
• directory: System.Directory
• old-time: System.Time
• old-locale: System.Locale

(dependency graph of the boot libraries)

These boot packages are included with ghc-6.8. If your package imports any of these modules, you need only add the corresponding packages to the build-depends line in your cabal file. However if you want to support both ghc-6.6 and ghc-6.8 you need to use the configurations feature in your .cabal file. For example:

flag splitBase
  description: Choose the new smaller, split-up base package.

library
  if flag(splitBase)
    build-depends: base >= 3, pretty, directory, old-time, process, containers
  else
    build-depends: base < 3

This is a simplified excerpt from Cabal's own Cabal.cabal file.

Data.ByteString api changes

module Data.ByteString.Base has been split into two. The "unsafe" functions moved to Data.ByteString.Unsafe and the others moved into Data.ByteString.Internal. The stable API going forward is all the modules exposed by the bytestring package except for the .Internal modules and the .Fusion module.

The lazy bytestring representation type has changed. Instead of a newtyped list:

newtype ByteString = LPS [Strict.ByteString]

it is now:

data ByteString = Empty | Chunk !Strict.ByteString ByteString

The crucial difference is that in the latter representation we can unpack the strict bytestring into the Chunk constructor which reduces the number of indirections to get at the string data from two to one.