HLint (formerly Dr. Haskell) reads Haskell programs and suggests changes that hopefully make them easier to read. HLint also makes it easy to disable unwanted suggestions, and to add your own custom suggestions.
$ hlint darcs-2.1.2 CommandLine.lhs:49:1: Warning, eta reduce Found: quotedArg ftable = between (char '"') (char '"') $ quoteContent ftable Why not: quotedArg = between (char '"') (char '"') . quoteContent CommandLine.lhs:94:1: Error, use concatMap Found: concat $ map escapeC s Why not: concatMap escapeC s Ssh.hs:155:17: Error, use isPrefixOf Found: take 1 path == "~" Why not: "~" `isPrefixOf` path ... many other suggestions ...
HLint can only be compiled by GHC 6.10.1 or above (it makes use of view patterns), but does not require any copy of GHC to run. HLint should be able to give hints for any Haskell code, including most GHC extensions. As with any good tool, HLint has been used in the development of itself, and all suggestions have been fixed.
- Haskell Style Scanner - check for poor layout/spacing etc.