[jhc] Typechecker hiccup?

I just tried to compile this program (based on figure one in "The GRIN Project: A Highly Optimising Back End for Lazy Functional Languages"): {-# OPTIONS_JHC -N -fffi #-} import Jhc.Basics import Jhc.Int import Jhc.Num import Jhc.Order default (Integer, Double) main = sum (upto 1 10) upto m n | m > n = [] | otherwise = m : upto (m+1) n sum [] = 0 sum (x:xs) = x + sum xs And I got a stupid error about a missing "put" method for IORef. It seems that the typechecker isn't getting rid of all the MetaVars in this program...