I just did "pacman -Syu", and among other things, it included an ncurses update:

Now things like ghci, ghc-pkg, etc fail with "error while loading shared libraries: libncursesw.so.5: cannot open shared object file: No such file or directory"

There's a libncursesw.so.6 instead, now. I suspect the ArchHaskell-provided GHC needs rebuilding against the newer ncurses?