Upgrading packages/Updating to GHC 7
A list of common problems upgrading packages to GHC 7.
If you maintain packages, this is for you.
If you use -XGADTs or -XTypeFamilies (or -fglasgow-exts, which is deprecated) you get -XMonoLocalBinds, which says that local let/where bindings are not auto-generalised. There's an extensive discussion of the reason for this decision in our paper "Let should not be generalised" and the journal version
base 3 goes away
There is no base 3 now, after being deprecated for several years, so dependencies on base 3 won't compile with GHC 7.
Quasiquotation data constructor modified
The QuasiQuoter constructor now takes four arguments instead of 2. (quoteType and quoteDec were added). One solution: use record syntax to set only the quoters you provide. This allows code to remain backwards compatible.
Quasiquotation: [$foo|...|] -> [foo|...|]
Quasiquoter invocation no longer requires/allows a leading dollar sign.
The binary library shipped with the compiler is renamed ghc-binary
If your package expects to see binary, the correct thing is to build and install an external version. However, you will need a version newer than 0.5.0.2, which was the current version in hackage when this was written.