GHCi doesn't load weak symbols
GHCi fails to load modules with weak symbols. The compiler, in contrast, has no trouble with them. The attached Cabal package demonstrates the problem. After building and installing:
:Prelude> :m +WeakTest Prelude WeakTest> weak_test 0 Loading package WeakTest-0 ... linking ... <interactive>: /home/heatsink/.cabal/lib/WeakTest-0/ghc-6.10.3/HSWeakTest-0.o: unknown symbol `weak_test'
I encountered this problem while trying to build a package that contains C++ code. Because GCC generates weak symbols when compiling C++, libraries that contain C++ code will not work in GHCi. (Granted, this is not the only problem with mixing C++ and Haskell.)