Upgrading packages/Updating to GHC 6.10
A list of things that need updating when porting packages to newer library/cabal versions.
If you maintain a Haskell package this is for you. For older versions of this document:
Updating to GHC 6.10 and Cabal 1.6
When upgrading to GHC 6.10, any of your packages that worked against the base-3 library will continue to work. GHC 6.10 provides both the old base-3 library and the new base-4.
To ensure your old code continues to work, you can have the code compile and link against base-3, and then, over time, migrate code to the base-4 series.
Adding base-3 constraints
How to do this depends on how you build your Haskell code. We'll start with the most simplistic build mechanisms. cabal-install, the most sophisticated tool, will sort this all out for you anyway, so things should change.
ghc --make
Force use of package base-3 when using --make,
ghc --make --package base-3.0.3.0
runhaskell
If you build your packages with the 'runhaskell Setup.hs configure' method, then you can force the use of base-3,
--constraint="base<4"
cabal-install
It is worth upgrading cabal-install immediately (maybe before installing GHC). This way you can use the smart dependency solver to work out what to install for you.
* install HTTP from hackage * install zlib from hackage
Then build cabal-install.
You can also override the dependencies when using the 'cabal' binary, with
--constraint="base<4"
Typical breakages with GHC 6.10
54 new packages break with the current GHC 6.10 release candidate.
The primary reasons are:
- Changes to Arrow class definition
- Changes to Map monadic types
- Cabal changes
- Changes to ghc-api
- Changes to when 'forall' is parsed
- GHC.Prim was moved,
- Changes to -fvia-C and headers?
- GADT changes,
- pragma warnings tightened
- Integer constructors have moved
- New warnings and used -Werror
- Exception handling: catch, finally, throwIO don't work anymore
Each of these has a standard way to solve the problem. Techniques should be attached here.
Backwards compatibility
The new, suggested Cabal version range syntax,
build-depends: base-3.*
is not backwards compatible with older versions of Cabal. Users will need to upgrade to the newer Cabal to build packages that start using this syntax.