On Tue, 19 Jun 2007, Stefan O'Rear wrote:
Like all good UNIX compilers, GHC will only print warnings if you ask it to, with -Wincomplete-patterns (iirc). -Wall enables most of them, the full list is in The Glorious Glasgow Haskell Compilation System User's Guide (a valuable read!)
Since GHC is not a C compiler (philosophy: "the programmers knows what he does") but a Haskell compiler (philosophy: "assist the programmer on finding mistakes") the warnings should be on by default, to encourage good programming style and find mistakes early. "Non-exhaustive patterns" often indicates possible situations for crashes. "unused identifier" often indicates that one has not completed the implementation of a function. Unfortunately GHC-6.4 warns about unnecessarily imported modules, but when you remove the import statement, some identifiers are missing.