There is an older stable version, but it doesn't work with ghc 6.12.3. Newer versions require Stream, which needs QuickCheck-2, which needs extensible-exceptions which we haven't got in portage yet.
Old and broken.
Needs to be bumped from hackage.
Version 2.8.0 claims to work with ghc 6.10, but it seems to be already broken with ghc 6.12.
Depends on cabal-1.1.6.2, needs to be bumped from the overlay.
New version from the overlay has more dependencies than the old version in portage. Need testpack.
Probably hasn't worked in a long time.
New cabal based versions are available in hackage. Partially put into the overlay, but nothing finished, iirc.