Hi all, a student of mine was puzzled by the following output, where, what appears to be equivalent expressions, yields non-equivalent results: ======================================================================== kahl@dionysos:/tmp/will > hugs Tree.hs __ __ __ __ ____ ___ _________________________________________ || || || || || || ||__ Hugs 98: Based on the Haskell 98 standard ||___|| ||__|| ||__|| __|| Copyright (c) 1994-1999 ||---|| ___|| World Wide Web: http://haskell.org/hugs || || Report bugs to: hugs-bugs@haskell.org || || Version: February 2000 _________________________________________ Haskell 98 mode: Restart with command line option -98 to enable extensions Reading file "/usr/global/share/hugs/lib/Prelude.hs": Reading file "Tree.hs": Hugs session for: /usr/global/share/hugs/lib/Prelude.hs Tree.hs Type :? for help Main> printH (listToTree [1,2,3,4,5]) [] [1]--| [] [2]--| [] [3]--| [] [5]--| [] [4]--| [] Elapsed time (ms): 20 (user), 10 (system) Main> listToTree [1,2,3,4,5] Node 5 (Node 4 (Node 3 (Node 2 (Node 1 Empty Empty) Empty) Empty) Empty) Empty Elapsed time (ms): 20 (user), 0 (system) Main> printH (Node 5 (Node 4 (Node 3 (Node 2 (Node 1 Empty Empty) Empty) Empty) Empty) Empty) [] [5]--| [] [4]--| [] [3]--| [] [2]--| [] [1]--| [] Elapsed time (ms): 30 (user), 0 (system) ======================================================================== for the following definitions: ======================================================================== data Tree a = Empty | Node a (Tree a) (Tree a) deriving Show insert :: (Ord a, Show a) => Tree a -> a -> Tree a insert Empty a = Node a Empty Empty insert (Node a left right) new | new < a = Node a (insert left new) right | otherwise = Node a left (insert right new) listToTree :: (Ord a, Show a) => [a] -> Tree a listToTree [] = Empty listToTree (x:xs) = insert (listToTree xs) x printH :: ((Ord a, Show a) => Tree a) -> IO() -- Problem here! printH t = putStr (hilf1 t 0) hilf1 :: (Ord a, Show a) => Tree a -> Int -> String hilf1 Empty space = replicate space ' ' ++ "[]\n" hilf1 (Node a left right) space = hilf1 right newspace ++ replicate space ' ' ++ "[" ++ show a ++ "]--|\n" ++ hilf1 left newspace where newspace = space + length (show a ++ "[]-|") ======================================================================== I know the problem lies in the illegal parentheses on line 14, and I suspect this triggers defaulting. The following seems to support this at least partially: Main> printH (listToTree [1::Integer,2,3,4,5]) [] [1]--| [] [2]--| [] [3]--| [] [5]--| [] [4]--| [] Main> printH (listToTree [1::Int,2,3,4,5]) [] [5]--| [] [4]--| [] [3]--| [] [2]--| [] [1]--| [] However, I still have Main> (4 :: Integer) < (5 :: Integer) True Main> (5 :: Integer) < (4 :: Integer) False So it does not seem to be a bug in Integer comparison. In addition I do not understand 1) why Hugs accepts these parentheses (without -98) (btype has no context) 2) why this is the result of accepting them. I am not on hugs-bugs. Best regards, Wolfram