From Hat's webpage: "Hat is a source-level tracer for Haskell 98, the standard lazy functional programming language. Hat is a tool that gives the user access to otherwise invisible information about a computation." This ebuild depends on having GHC (the program can also run on nhc98, but as it doesn't appear to be in portage, the ebuild lists itself as depending on GHC) and hmake.
Created attachment 98646 [details] Hat 2.04 ebuild
Seems upstream was abandoned some years ago and uses dropped hmake. We would pick hat if it would be ported to recent ghc versions (and ideally would use Cabal as a build system), but not in it's current form, sorry. Closing as WONTFIX. Feel free to reopen when upstream will awake. Thanks for the ebuild though! Sorry for 5 years long delay.