Hi, Printing the core one of my programs I see: data Prelude;1() a = Preluse;1() a What is this? A single element tuple? I didn't think Haskell had these. My program has a monad similar to IO. It appears these Prelude;1() things are created in the lambda lifted version of f1. Perhaps is it the parenthesis around (System m)? data Return a = Return a World data System a = System (World -> Return a) data World = World instance Monad System where (System m) >>= k = System f1 where f1 w = f2 w' where Return r w' = m w System f2 = k r return a = System (\ w -> Return a w) It's a bit difficult to correlate arguments of lifted lambdas to the original source. Is there a convention YHC uses for adding the extra arguments to lifted lambdas? Thanks! -Tom