Can't compile haskell project: linking step fails

Question

I'm having issues doing a cabal run on my project. This project used to run properly, and I'm not totally sure what change broke it. I think it is related to the issues between GHC 7.6 and OSX Mavericks (I'm using Darin Morrison's homebrew formulae here). [Edit: to clarify, this was working at one point on Mavericks, so this hypothesis may not hold up.] The problem appears to be in the linking step:

In-place registering chorez-0.1.0.0...
Preprocessing executable 'chorez' for chorez-0.1.0.0...
Linking dist/build/chorez/chorez ...
Undefined symbols for architecture x86_64:
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_AddResponse_con_info", referenced from:
      _s5X4_info in libHSchorez-0.1.0.0.a(Commands.o)
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_ErrorResponse_static_info", referenced from:
      _chorezzzm0zi1zi0zi0_ChorezzziCommands_route1_closure in libHSchorez-0.1.0.0.a(Commands.o)
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_parseRequest_closure", referenced from:
      _r7eV_srt in libHSchorez-0.1.0.0.a(Server.o)
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_parseRequest_info", referenced from:
      _s7nh_info in libHSchorez-0.1.0.0.a(Server.o)
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_zdfToJSONResponse1_closure", referenced from:
      _r7eS_closure in libHSchorez-0.1.0.0.a(Server.o)
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_zdfToJSONResponse4_closure", referenced from:
      _s7ng_info in libHSchorez-0.1.0.0.a(Server.o)
      _r7eQ_closure in libHSchorez-0.1.0.0.a(Server.o)
      _r7eV_srt in libHSchorez-0.1.0.0.a(Server.o)
  "_chorezzzm0zi1zi0zi0_ChorezzziRequest_zdfToJSONResponse5_closure", referenced from:
      _s7ng_info in libHSchorez-0.1.0.0.a(Server.o)
      _r7eV_srt in libHSchorez-0.1.0.0.a(Server.o)
ld: symbol(s) not found for architecture x86_64
collect2: ld returned 1 exit status

All of these symbols are from my own project (judging by the names). Most answers that I've seen about this have to do with a certain library not linking properly. I suspect some of these symbols are generated by deriveToJSON from Data.Aeson.TH. I've reinstalled a couple of times with no resolution. Any ideas?

Answer 1

Here's what finally fixed it. My cabal config was something like this:

library
  exposed-modules:
      My.Module1
    , My.Module3


executable my-executable
  main-is:             Main.hs
  build-depends:
      base >=4.6 && <4.7
    , chorez

Main.hs for the executable imports My.Module3. My.Module3 imports the private My.Module2. Including My.Module2 under exposed-modules fixed the issue. I figured this out because I realized that all the symbols that couldn't be found came from that module. cabal repl worked just fine (I tested the modules by hand and they all basically worked), but cabal run didn't. I feel like I should be able to use a library with private modules in an executable, but in this case I just forgot to add the new module to the list, and I have no reason to make any module private, so I'm up and running for now.