[Haskell-cafe] Higher-order unification

[Simon Peyton-Jones]

| Yeah, here's a program which causes GHC to hang on compilation, but
| causes no problem for hugs.  Does this qualify as higher-order
unification?
| 
| newtype X a = X (X a -> a)
| 
| selfapp :: X a -> a
| selfapp self@(X f) = f self

It's a documented bug in GHC.  
http://www.haskell.org/ghc/docs/latest/html/users_guide/bugs.html
Nothing to do with h-o unification

Simon