Hello, I'm trying to figure out how you tell if ghc has correctly infered strictness or whether or not a little more prompting from me is needed. I tried compiling with -ddump-simpl, and I guess from looking at this the DmdType bit is what I want (maybe). So if I have "DmdType LS" for a function of arity 2, does this mean the function is lazy in the first argument and strict in the second? I would be pretty confident that this was the correct interpretation, but this is the Haskell code (from AVL library).. height :: AVL e -> Int height = addHeight 0 where addHeight h E = h addHeight h (N l _ _) = addHeight h+2 l addHeight h (Z l _ _) = addHeight h+1 l addHeight h (P _ _ r) = addHeight h+2 r It seems pretty obvious to me that addHeight is strict in its first argument if + is strict for Ints (as I guess it is). But this gives "DmdType LS". Even if I rewrite it.. height :: AVL e -> Int height = addHeight 0 where addHeight h E = h addHeight h (N l _ _) = let h' = h+2 in h' `seq` addHeight h' l addHeight h (Z l _ _) = let h' = h+1 in h' `seq` addHeight h' l addHeight h (P _ _ r) = let h' = h+2 in h' `seq` addHeight h' r .. it still gives "DmdType LS". So does this.. height :: AVL e -> Int height = addHeight 0 where addHeight h E = h addHeight h (N l _ _) = h `seq` addHeight (h+2) l addHeight h (Z l _ _) = h `seq` addHeight (h+1) l addHeight h (P _ _ r) = h `seq` addHeight (h+2) r So am I interpreting core correctly? Thanks -- Adrian Hey