All, I've tried building 1324 out of the ~1700 packages from hackage using ghc-6.10.4 and ghc-6.12.0. This is the subset of packages that I could build in one go. Compared to the subset that I could build with ghc-6.10.4, I had to chuck out 125 packages because their build dependency constraints precluded them from building with ghc-6.12. Of the remaining 1324 packages, 113 packages that built OK previously now do not build. Amongst that 113, the ones that cause most knock-on failures are: (16,"packedstring-0.1.0.1") (12,"MissingH-1.1.0.1") (11,"syb-with-class-0.5.1") (6,"uvector-0.1.0.5") (3,"stringtable-atom-0.0.6") (3,"bindings-common-1.3.4") (3,"binary-strict-0.4.6") (3,"base64-string-0.1") packedstring fails because it needs base 4, but only says "build-depends: base", so cabal uses its compatibility tricks and builds it against base 3. It should specify "build-depends: base == 4.*". I need to investigate MissingH further. It failed because a dependency of its non-buildable test program was not found. That should not have been a problem. syb-with-class has type errors, I'm guessing due to changes in template-haskell package uvector does not compile because of the changes in GHC's Handle implementation. stringtable-atom now fails with a type error for reasons I don't quite understand: src/StringTable/AtomMap.hs:320:0: Occurs check: cannot construct the infinite type: a = (Int, a) When generalising the type(s) for `findMax' Perhaps some change in a containers function? bindings-common and c2hs fail because the CLDouble FFI type has been removed. binary-strict fails because the export of Control.Applicative.many now clashes with a local definition. base64-string fails because it sets -Werror in it's .cabal file (a practise which has been banned for some time for just this reason). Of the remaining 113: 2 failed at the configure step: MissingH-1.1.0.1 -- this needs investigation, I smell a cabal bug lax-0.1.0.0 52 failed at the build step (including those singled out above): ArrayRef-0.1.3.1 -- ghc Handle changes Boolean-0.0.0 -- name clash with Control.Applicative.<* CCA-0.1.1 -- TH changes, missing Lift instances ChasingBottoms-1.2.4 -- name clash with Data.Sequence.partition ChristmasTree-0.1.2 -- TH changes (Name vs TyVarBndr) HCodecs-0.1 -- Data.Array.Diff disappeared HList-0.2 -- change in GADT syntax (context) MonadLab-0.0.2 -- Some API change, not immediately obvious base64-string-0.1 -- described above binary-strict-0.4.6 -- described above bindings-common-1.3.4 -- described above bindings-gsl-0.1.1.6 -- CLDouble bloomfilter-1.2.6 -- declaration of a type or class operator `:*' bytestringparser-0.3 -- -Werror c2hs-0.16.0 -- CLDouble cabal2arch-0.6 -- Cabal API changes cabal2doap-0.2 -- Cabal API changes compact-map-2008.11.9 -- GHC Handle changes conjure-0.1 -- Data.Array.Diff disappeared flock-0.1 -- -Werror fail gtk2hs-cast-gtk-0.10.1.2-- type error, not immediately obvious hask-home-2009.3.18 -- Cabal lib API changes hgalib-0.2 -- Data.Array.Diff disappeared hircules-0.3.92 -- ambiguity GHC.IO.liftIO vs C.M.State.liftIO hnop-0.1 -- -Werror fail hommage-0.0.5 -- GHC.IO changes hxt-filter-8.3.0 -- name clash System.IO.utf8 and local name ideas-0.5.8 -- A pattern match on a GADT requires -XGADT ieee-0.6 -- CLDouble ivor-0.1.9 -- 'rec' now a keyword loch-0.2 -- -Werror fail nano-hmac-0.2.0 -- -Werror fail nanocurses-1.5.2 -- package specifies non-existant config.h (which used to accidentally pick up ghc's config.h) this happens because the package needs to run ./configure but does not say so. network-fancy-0.1.4 -- GHC Handle changes pkggraph-0.1 -- Cabal lib API changes plugins-1.4.1 -- Cabal lib API changes posix-realtime-0.0.0.1 -- type of internal IOError constructor printf-mauke-0.3 -- CLDouble pugs-HsSyck-0.41 -- mdo syntax removed? random-fu-0.0.3 -- type error, not immediately obvious rdtsc-1.1.1 -- -Werror fail repr-0.3.1 -- same as random-fu safe-lazy-io-0.1 -- GHC Handle changes sendfile-0.5 -- GHC Handle changes sessions-2008.7.18 -- needs -XTypeOperators stringtable-atom-0.0.6 -- described above syb-with-class-0.5.1 -- described above type-settheory-0.1.2 -- TH lib API changes uu-parsinglib-2.3.0 -- scoped type var changes? uuagc-0.9.12 -- 'rec' now a keyword uvector-0.1.0.5 -- GHC Handle changes word24-0.1.0 -- Not in scope: `divZeroError' The remaining 59 are knock-on failures, ie packages that depended on one of the failed packages. Duncan