I believe I have run headlong into issue #3064 in ghc (http://hackage.haskell.org/trac/ghc/ticket/3064). All I think I know is this: * this is a performance issue with the system used to solve type constraints. * the solver is undergoing an overhaul to resolve performance issues in addition to other issues. * An efficient constraint solver is difficult. NP-Complete in the general case? Beyond that I'm at a loss. What can I read to understand the constraint satisfaction problem as it stands in GHC? Is there a paper on the implementation of the current solver? Anything on how the new solver will differ from the current? I think I located one page on the new solver: http://hackage.haskell.org/trac/ghc/wiki/TypeFunctionsSolving Cheers, Corey O'Connor