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

[David Feuer]

Congrats! I look forward to seeing how this develops.

On Sun, Sep 4, 2016 at 11:27 AM, lennart spitzner
<lsp at informatik.uni-kiel.de> wrote:
> 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
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