[Haskell-cafe] [ANN] brittany - haskell source code formatting tool - experimental/alpha

Greetings, I am happy to announce a first alpha release of brittany (0.7.0.0), a haskell source code formatting tool based on ghc-exactprint [2] (and thus ghc's parser). https://github.com/lspitzner/brittany Two small feature cases that brittany would produce/leave unmodified: > -- Newlines are used sparingly: Only after "do" and when the > -- `liftBaseOpDiscard` application would lead to overflowing 80 columns. > main :: IO () > main = do > pool <- createPostgresqlPool (toS databaseConnectionString) 10 > initiate $ \chan -> forever $ do > flip runDbConn pool $ do > makeSureQueueIsFull chan > void $ liftBaseOpDiscard (consumeMsgs chan responseQueue Ack) > (uncurry processMsg) > threadDelay 1000000 > -- Alignment of patterns > go [] "" = True > go [WildCard ] "" = True > go (WildCard :rest) (c:cs) = go rest (c : cs) || go (WildCard : rest) cs > go (Union globs:rest) cs = any (\glob -> go (glob ++ rest) cs) globs > go [] (_:_) = False > go (_:_) "" = False Yet this is an alpha release, for the following reasons: - Brittany currently only transforms top-level type signatures and (function) bindings. - Not all syntactical constructs (even of plain 2010 haskell) are understood. All common constructs should work, but "common" is purely subjective. - Not all (syntactic) extensions are supported, either. - Needs more testing. (And less than a hundred automated testcases is not very much to explore every syntactic corner of haskell.) On the other hand - I have started using the tool successfully, albeit selectively. - There are checks in place that detect 1) if output is not valid haskell or 2) if source comments are not transcribed to the output. That is, running into non-handled cases should lead to error messages that are harmless, not into any silent it-overwrote-my-code-with-garbage. *How to build?* Brittany requires ghc-8. See https://github.com/lspitzner/brittany#building A hackage release is not planned yet. *Brittany's formatting style* Currently brittany does _not_ give the user many choices. A few flags exist, most prominently to change the indentation (default 2) or the columns (default 80). I am open to suggestions of how to improve the style, but trying to make everyone happy is not a fulfilling goal for me. *Implementation/documentation/performance* The implementation and its core ideas are not documented. The core algorithm in theory has linear complexity in input size; the implementation probably is quadratic dues to some misuses of plain lists or other such implementation details. Providing at least a high-level overview is on my to-do list. [1] https://github.com/lspitzner/brittany [2] https://hackage.haskell.org/package/ghc-exactprint -- lennart