Note that you may find old references to JHC laying around. GHC 6.12 included support for shared libraries, so the current version of Hubris uses GHC, a more mature and common Haskell compiler.
Hubris requires that ruby has been built with dynamic libraries. The latest version of RVM does this, earlier ones may not. Unfortunately, because GHC only produces i386 executables on Mac, the libruby.dylib must also be an i386 library.
You can test this by running “file /path/to/libruby.dylib” – it should say it’s i386, not x86_64. RVM will build an i386 lib for you with this incantation: