A problem that has plagued my GHC installation for a while is that whenever I tried to install any non-trivial package I would get a horrible link error like this:

Undefined symbols:
"_iconv_close", referenced from:
_hs_iconv_close in libHSbase-4.3.1.0.a(iconv.o)
(maybe you meant: _hs_iconv_close)
"_iconv_open", referenced from:
_hs_iconv_open in libHSbase-4.3.1.0.a(iconv.o)
(maybe you meant: _hs_iconv_open)
"_iconv", referenced from:
_hs_iconv in libHSbase-4.3.1.0.a(iconv.o)
(maybe you meant: _hs_iconv_open, _hs_iconv_close , _hs_iconv )
"_locale_charset", referenced from:
_localeEncoding in libHSbase-4.3.1.0.a(PrelIOUtils.o)
collect2: ld returned 1 exit status


The reason for this is a combination of several factors:

• The base library that comes with the GHC binary distribution wants to link against the standard Mac iconv

• I have installed MacPorts libiconv, which renames the function that is named iconv_open in the standard iconv to libiconv_open

• The Haskell library being installed by cabal depends transitively on some library that was built with something like extra-lib-dirs: /opt/local/lib, which causes -L/opt/local/lib to be passed to the linker

• The linker’s -L/opt/local/lib option occurs before -L/usr/lib, so the linker prefers to link against the MacPorts libiconv instead of the system one

In my case, it was the Haskell readline wrapper that was causing /opt/local/lib to be pulled in. I had to link the Haskell readline against MacPorts readline because the standard Mac libreadline is actually libeditline, which is almost-but-not-quite compatible and misses some crucial features.

There are several ways to fix the problem:

• Perhaps you don’t really need the MacPorts libiconv. In this case, you can stop it from being used by just doing port deactivate libiconv. This is the route I took.

• Perhaps it’s OK to link this particular library against the system libraries in preference to the MacPorts one. In this case, you can configure the package with cabal configure --extra-lib-dir=/usr/lib, so /usr/lib is searched before the MacPorts directory. This may fail if the package that needed -L/opt/local/lib requires a MacPorts version of some library that is also present in /usr/lib, though.

• You could build GHC yourself and link it against the MacPorts library versions. This is not for the faint-hearted, but if the version of GHC you need is in MacPorts I imagine that you can just do port install ghc

I’m glad I’ve finally got this sorted out. If you are still having trouble, you might find some helpful information in the threads that finally helped me to overcome the issue and prompted this writeup.