Q:

wxHaskell fails because it depends on wx_macu-2.8

I install wxWidgets with macports then ran the command: sudo cabal install wx which output included:
/bin/sh: wxdirect: command not found
/bin/sh: wxdirect: command not found
/bin/sh: wxdirect: command not found
/bin/sh: wxdirect: command not found
Configuring wxcore-0.12.1.6...
setup: Missing dependency on a foreign library:
* Missing C library: wx_macu-2.8
This problem can usually be solved by installing the system package that
provides this library (you may need the "-dev" version).  If the library is
already installed but in a non-standard location then you can use the flags
--extra-include-dirs= and --extra-lib-dirs= to specify where it is. 
cabal: Error: some packages failed to install:
wx-0.12.1.6 depends on wxcore-0.12.1.6 which failed to install. 
wxcore-0.12.1.6 failed during the configure step.  The exception was:
ExitFailure 1

I got the same error when I used this command: sudo cabal install wx --extra-include-dirs=/opt/local --extra-lib-dirs=/opt/local.  How can I install wx_macu-2.8, or do what I need to do to fix this problem? 

A:

This is saying that you are missing a C library, not a Haskell library.   Cabal can't install arbitrary C libraries.   
Check the package manager for your distribution to make sure you have everything to do with wxWidgets-2.8, including any developer packages.