Hi, the following example causes ghc to loop (or run rather long): --- snip --- data U = MkU (U -> Bool) russel :: U -> Bool russel u@(MkU p) = not $ p u x :: Bool x = russel (MkU russel) --- snip --- I think, a compiler should always terminate, shouldn't it!? Compilation succeeds for "russel $ MkU russel" instead of "russel (MkU russel)". (Surely, x is bottom and therefore the example is senseless) Regards Christian