I was unable to install happstack-data-0.4.1 on windows with GHC 6.12.1. Here the log: Resolving dependencies... Configuring happstack-data-0.4.1... Preprocessing library happstack-data-0.4.1... Preprocessing executables for happstack-data-0.4.1... Building happstack-data-0.4.1... src\Happstack\Data\GOps.hs:54:0: warning: no newline at end of file src\Happstack\Data\SerializeTH.hs:88:0: warning: no newline at end of file [ 1 of 16] Compiling Happstack.Data.GOps ( src\Happstack\Data\GOps.hs, dist\buil d\Happstack\Data\GOps.o ) src\Happstack\Data\Serialize.hs:1:85: Warning: -XPatternSignatures is deprecated: use -XScopedTypeVariables or pra gma {-# LANGUAGE ScopedTypeVariables #-} instead src\Happstack\Data\Xml\Base.hs:6:13: Warning: -XPatternSignatures is deprecated: use -XScopedTypeVariables or pra gma {-# LANGUAGE ScopedTypeVariables #-} instead [ 2 of 16] Compiling Happstack.Data.Normalize ( src\Happstack\Data\Normalize.hs, dist\build\Happstack\Data\Normalize.o ) [ 3 of 16] Compiling Happstack.Data.Migrate ( src\Happstack\Data\Migrate.hs, dis t\build\Happstack\Data\Migrate.o ) [ 4 of 16] Compiling Happstack.Data.Default ( src\Happstack\Data\Default.hs, dis t\build\Happstack\Data\Default.o ) [ 5 of 16] Compiling Happstack.Data.DeriveAll ( src\Happstack\Data\DeriveAll.hs, dist\build\Happstack\Data\DeriveAll.o ) [ 6 of 16] Compiling Happstack.Data.Default.Generic ( src\Happstack\Data\Default \Generic.hs, dist\build\Happstack\Data\Default\Generic.o ) [ 7 of 16] Compiling Happstack.Data.Xml.Base ( src\Happstack\Data\Xml\Base.hs, d ist\build\Happstack\Data\Xml\Base.o ) Loading package ghc-prim ... linking ... done. Loading package integer-gmp ... linking ... done. Loading package base ... linking ... done. Loading package array-0.3.0.0 ... linking ... done. Loading package bytestring-0.9.1.5 ... linking ... done. Loading package containers-0.3.0.0 ... linking ... done. Loading package pretty-1.0.1.1 ... linking ... done. Loading package template-haskell ... linking ... done. Loading package syb-with-class-0.6.1 ... linking ... done. Loading package HUnit-1.2.2.1 ... linking ... done. Loading package syb-0.1.0.2 ... linking ... done. Loading package base-3.0.3.2 ... linking ... done. Loading package Win32-2.2.0.1 ... linking ... done. Loading package old-locale-1.0.0.2 ... linking ... done. Loading package time-1.1.4 ... linking ... done. Loading package random-1.0.0.2 ... linking ... done. Loading package QuickCheck-1.2.0.0 ... linking ... done. Loading package extensible-exceptions-0.1.1.1 ... linking ... done. Loading package mtl-1.1.0.2 ... linking ... done. Loading package old-time-1.0.0.3 ... linking ... done. Loading package parsec-2.1.0.1 ... linking ... done. Loading package hsemail-1.3 ... linking ... done. Loading package network-2.2.1.7 ... linking ... done. Loading package SMTPClient-1.0.1 ... linking ... done. Loading package filepath-1.1.0.3 ... linking ... done. Loading package directory-1.0.1.0 ... linking ... done. Loading package process-1.0.1.2 ... linking ... done. Loading package hslogger-1.0.7 ... linking ... done. Loading package deepseq-1.1.0.0 ... linking ... done. Loading package parallel-2.2.0.1 ... linking ... done. Loading package strict-concurrency-0.2.2 ... linking ... done. Loading package unix-compat-0.1.2.1 ... linking ... done. Loading package happstack-util-0.4.1 ... linking ... done. Loading package binary-0.5.0.2 ... linking ... done. Loading package haskell98 ... linking ... done. Loading package HaXml-1.13.3 ... linking ... done. Loading package ffi-1.0 ... linking ... done. ghc.exe: dist\build\Happstack\Data\Default.o: unknown symbol `_sybzmwithzmclassz m0zi6zi1_DataziGenericsziSYBziWithClassziInstances_constrZMacbsZN_closure' cabal: Error: some packages failed to install: happstack-data-0.4.1 failed during the building phase. The exception was: ExitFailure 1 I can create more detailed log if you need.