[Haskell] Haskell Digest, Vol 168, Issue 3
Geraldus
heraldhoi at gmail.com
Sun Aug 6 07:46:09 UTC 2017
Wow, looks very promising.
сб, 5 авг. 2017 г. в 17:29, <haskell-request at haskell.org>:
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> Today's Topics:
>
> 1. [ANN] brittany - haskell source code formatting tool -
> hackage release (lennart spitzner)
>
>
> ----------------------------------------------------------------------
>
> Message: 1
> Date: Fri, 4 Aug 2017 15:01:51 +0200
> From: lennart spitzner <hexagoxel at hexagoxel.de>
> To: undisclosed-recipients: ;
> Subject: [Haskell] [ANN] brittany - haskell source code formatting
> tool - hackage release
> Message-ID: <14f23926-b296-865d-7eeb-1a232427fd07 at hexagoxel.de>
> Content-Type: text/plain; charset=utf-8
>
> Greetings,
>
> I am happy to (finally) announce the first hackage release of brittany, a
> configurable haskell source code formatter based on ghc-exactprint [2].
>
> https://hackage.haskell.org/package/brittany
> https://github.com/lspitzner/brittany
>
>
> *Introduction*
>
> Brittany aims to nicely layout the code and retain empty lines and
> comments as
> they appear in the input. For that it uses a fundamentally different
> approach
> (see [7]/theory) than other formatters. The project is not finished, yet it
> already is usable and produces better results than other formatters in many
> cases. Of course these words come from its creator, so see for yourself: I
> have included some examples at the bottom of this mail; see [3] and [4] for
> some more.
>
> I wish to stress that this project will only progress at a very slow speed
> barring support from the community. I hereby offer to work on this and ask
> for funding. See the "future" paragraph below.
>
>
> *Changelog*
>
> Since the "alpha-release" announced previously [5] the most important
> changes
> are:
>
> - Release under the AGPL-v3;
> - Release on hackage;
> - Make horizontal alignment less aggressive by default (see example [6]);
> - Add high-level documentation (see [7]). This might be of interest to
> anyone
> considering to write a formatter (haskell or even otherwise);
> - Improve testsuite setup;
> - Improve layouting in many many cases and fix various bugs;
> - Add a library interface (this integrates with haskell-ide-engine [8]);
>
> Brittany still..
>
> - does not touch anything other than top-level type signatures and
> bindings (imports, classes, instances, data decls, .. are not modified);
> - contains some bugs (but it checks its own output for validity and
> aborts);
> - does not handle many "uncommon" syntactic constructs/extentions
> (e.g. arrow notation);
>
> In preparation of this release the `butcher` and `czipwith` packages were
> published on hackage as well. I will cover those in separate announcements.
>
>
> *Building*
>
> Brittany currently requires ghc-8.0 (no support for previous ghc versions
> is
> planned, but 8.2 will be). Now that this package is on hackage, cabal users
> should be able to install it directly; stack users will currently have to
> clone
> and go from there (a stack.yaml is provided). Detailed building guides for
> cabal, cabal-new and stack are in the project README.
>
> Inclusion in stackage is coming as soon as all dependencies are included.
>
>
> *Known issues*
>
> - Bad performance for large inputs (really noticeable at >1k loc). The
> cause
> is already determined - quadratic instead of linear complexity in one
> specific function (see issue #34 [9]). Should be fixable and has high
> priority.
> - The config (file) lacks documentation.
> - Comments are not always reproduced exactly when reformatting. There is a
> lack
> of testcases for comments in the testsuite. There is the known case of
> comments in List/MonadComprehensions that currently breaks idempotency
> (the
> comments move further left each roundtrip through brittany) where a
> solution
> will most likely involve some non-trivial changes in ghc-exactprint
> (see [10]).
> - As mentioned above: only certain module elements are transformed, and
> not all syntactical constructs are supported. re-layouting of imports,
> data
> decls, classes and instances are on the radar, but all require a good
> amount
> of work.
> - CPP is not officially supported. This is mostly a WONTFIX. One can
> enable it
> by force, and it works to a degree, but it is relatively easy to find
> cases
> where it will break (conditional code not being reformatted, leading to
> syntax errors and theoretically also to change semantics)).
> - No fine-grained (per file or even per-function) control/configuration,
> e.g.
> it is not yet possible to add some pragma/comment to disable reformatting
> this one carefully layouted-by-hand function that brittany messes up.
> - No adaption to ghc-8.2 yet.
>
>
> *Future/Outlook*
>
> As far as I can tell brittany already works rather well - I use it all the
> time, even though I still run into issues from time to time. Still,
> brittany is
> not finished (these projects never really are, are they?).
>
> Up on my list are ghc-8.2 adaption, fixing the performance bug mentioned
> above,
> layouting of data decls, layouting of instances, and controlling
> behaviour/config via flags in the source (as comments).
> But implementing new functionality costs a lot of time, even with the DSL
> used
> internally: One has to understand the GHC AST (which is not always
> documented),
> think of all possible interactions ("do users really use record syntax when
> having more than one constructor?" "are GADT records a thing?"), write the
> layouting transformation and test it.
>
> I have already invested a good amount of my free time into this project
> but its
> scope is too large and I decided to put a limit on my personal investment.
> This means that barring some form of support from the community I don't
> see new
> features being implemented at any certain pace. This leaves the following
> paths:
>
> 1) This project is supported monetarily: I hereby offer to (part-time)
> work on
> this provided appropriate funding. I am not sure who exactly might be
> interested in providing this kind of support - I am no student anymore
> so
> GSoC is out of the question. Feel free to contact me on- or off-list if
> interested.
>
> 2) (More) Contributors add tests, report (and maybe fix) bugs and most
> importantly implement new functionality (layouting for any syntactic
> constructs of the haskell language not yet supported, etc.)
>
> I realize that this is not a trivial project to dive into, and there is
> a
> good amount of stuff one has to get familiar with before one can start
> making use of the abstractions (the DSL) provided.
>
> On the other hand, I _think_ that the project source code is relatively
> well-structured (although in-source comments are really sparse,
> admittedly)
> and the high-level (markdown) documentation <strike>will scare everyone
> away due to their length</strike> will allow understanding the project
> relatively quickly.
>
> 3) The project will progress only rather slowly.
>
> Regardless I plan to continue maintaining this project, fix bugs as they
> come
> up and also work on expanding functionality when I find the time.
>
>
> *Contributing*
>
> In ascending order of involvement, you can contribute by:
>
> - Reporting issues, especially instances of bad layouting (especially when
> it
> is not a pure matter of opinion);
> - Add to the testsuite, specifically to the `tests.blt` file of the
> `littests`
> test. It contains a large number of tests already, but the coverage is
> not
> very good.
> - If you want to really help implementing more stuff, the high-level docs
> [7]
> are the right place to get a rough overview, especially the theory
> document
> [11]. I have not documented how to write new layouters yet, so for now I
> recommend looking at the existing ones, e.g. in `Expr.hs`.
>
>
> -- lennart
>
>
> [1] https://hackage.haskell.org/package/brittany
> https://github.com/lspitzner/brittany/
> [2] https://mpickering.github.io/posts/2015-07-23-ghc-exactprint.html
> https://hackage.haskell.org/package/ghc-exactprint
> [3]
> https://github.com/lspitzner/brittany/blob/da692a4341399390018fb03773e15865d967fb8c/doc/showcases/BrittanyComparison.md
> [4] https://github.com/lspitzner/brittany/tree/master/doc/showcases
> [5]
> https://mail.haskell.org/pipermail/haskell-cafe/2016-September/124793.html
> [6]
> https://github.com/lspitzner/brittany/blob/da692a4341399390018fb03773e15865d967fb8c/doc/showcases/Layout_Alignment.md#items-that-are-not-single-line-break-up-alignment
> [7]
> https://github.com/lspitzner/brittany/blob/master/doc/implementation/index.md
> [8] https://github.com/haskell/haskell-ide-engine
> [9] https://github.com/lspitzner/brittany/issues/34
> [10] https://github.com/alanz/ghc-exactprint/issues/53
> [11]
> https://github.com/lspitzner/brittany/blob/master/doc/implementation/theory.md
>
>
> --
>
> some layouting examples - would be (re)produced in exactly this way by
> brittany:
>
> > main = do
> >
> > now <- getCurrentTime
> > let (_, _, week) = toWeekDate . utctDay $ now
> > putStrLn $ ("it's "++) $ case week of
> > 6 -> "the weekend"
> > 7 -> "the weekend"
> > _ -> "a weekday"
> >
> > localtime <- utcToLocalZonedTime now
> > let hr = todHour . localTimeOfDay . zonedTimeToLocalTime $ localtime
> > case hr of
> > _ | hr < 12 -> putStrLn "it's before noon"
> > | otherwise -> putStrLn "it's after noon"
>
> > -- 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
>
>
>
>
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> ------------------------------
>
> End of Haskell Digest, Vol 168, Issue 3
> ***************************************
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