Currently the following 32 library packages directly depending on mtl are broken by the changes (including reasons and number of packages that directly or indirectly depend on these): applicative-extras-0.1.6 Applicative instance (9 clients) blogination-0.5 Applicative instance (no clients) category-extras-0.53.5 Functor constraint (15 clients) csound-expression-0.0 base monad members (no clients) derive-2.3.0.2 Applicative instance (13 clients) encoding-0.6.3 base monad members (15 clients) FileManip-0.3.3.1 base monad members (13 clients) FileManipCompat-0.15 base monad members (7 clients) HaLeX-1.1.1 base monad members (no clients) happstack-server-0.5.0.2 Functor constraint (32 clients) hashed-storage-0.5.3 Functor constraint (6 clients) HaskellNet-0.2.3 base monad members (no clients) hmk-0.9.7 Applicative instance (1 clients) hssqlppp-0.2.0 Error instance (1 clients) jmacro-0.3.2 base monad instance (no clients) kibro-0.4.3 Functor constraint (11 clients) llvm-ht-0.7.0.0 base monad members (2 clients) monad-param-0.0.2 Functor constraint (no clients) MonadRandom-0.1.5 Functor constraint (13 clients) nntp-0.0.3 Functor constraint (no clients) OpenCLRaw-1.0.1001 base monad members (no clients) open-witness-0.1.1 base monad members (no clients) plot-0.1.2.3 base monad members (1 clients) random-fu-0.1.0.0 base monad instance (3 clients) redHandlers-0.1 Functor constraint (1 clients) she-0.1 Applicative instance (no clients) swish-0.2.1 base monad members (no clients) tls-0.2 Functor constraint (6 clients) Twofish-0.2 base monad instance (no clients) xmonad-contrib-bluetilebranch-0.9.1.4 base monad members (1 clients) yhccore-0.9.1 base monad instance (3 clients) A further concern is that we now have 138 packages whose dependencies exclude mtl-2 and 8 (and rising) whose dependencies require it. That will prevent an increasing number of packages from building.