pl a b = a ++ b pl a = a ++ The second definition cannot be accept by neigher ghci nor ghc. What's the problem? (ghc 6.12.3) -- ---------------- WU XingBo -------------- next part -------------- An HTML attachment was scrubbed... URL: <http://www.haskell.org/pipermail/beginners/attachments/20101210/527bab0a/attachment.htm>