Hi, Sorry to post to a list, but there are no other contact addresses on the haskell.org site or in the tutorial itself. Any replies, please also CC me as I do not subscribe to any haskell.org lists. I noticed an error in the Haskell Tutorial in section 8.3. The code for the Tree parser will not work. Specifically, the following is broken: readsTree :: (Read a) => ReadS (Tree a) readsTree s = [(Branch l r, x) | ("<", t) <- lex s, (l, u) <- readsTree t, ("|", v) <- lex u, (r, w) <- readsTree v, (">", x) <- lex w ] ++ [(Leaf x, t) | (x, t) <- reads s ] It will not read a string like "<<1|2>|3>" because of the "<<" which the lexer will see as one token. Here is another implementation: showsTree :: (Show a) => Tree a -> ShowS showsTree (Leaf x) = ("Leaf " ++) . shows x showsTree (Branch l r) = ("Branch (" ++) . showsTree l . (") (" ++) . showsTree r . (')':) readsTree :: (Read a) => ReadS (Tree a) readsTree s = [(Branch l r, v) | ("Branch", t) <- lex s, (l, u) <- readsTree t, (r, v) <- readsTree u ] ++ [(Leaf x, u) | ("Leaf", t) <- lex s, (x, u) <- reads t ] ++ [(x, v) | ("(", t) <- lex s, (x, u) <- readsTree t, (")", v) <- lex u ] instance Show a => Show (Tree a) where showsPrec _ x = showsTree x instance Read a => Read (Tree a) where readsPrec _ s = readsTree s This is almost equivalent to the derived one, but will accept strings like "Branch Leaf 3 Branch Branch Leaf 1 Leaf 2 Branch Leaf 5 Leaf 4" (that is, without the parentheses). Regards, Pete