- Haskell-Cafe - Haskell.org

C call blocking indefinitely/behaving differently when called from Haskell
by Oliver Charles 15 Aug '16

15 Aug '16

Hi all, I'm trying to interface with a Basler USB3 camera <http://www.baslerweb.com/en/products/> from a Haskell application, but I'm experiencing some difficulty. The camera comes with a C++ library that makes it fairly straight forward. The following code can be used to acquire a camera source: PylonAutoInitTerm pylon; CInstantCamera camera( CTlFactory::GetInstance().CreateFirstDevice()); camera.RegisterConfiguration( (CConfigurationEventHandler*) NULL, RegistrationMode_ReplaceAll, Cleanup_None); cout << "Using device " << camera.GetDeviceInfo().GetModelName() << endl; Using the inline-c and inline-c-cpp libraries, I am trying to perform this same call from a Haskell executable. I have the following: {-# LANGUAGE QuasiQuotes, TemplateHaskell #-} import qualified Language.C.Inline as C import qualified Language.C.Inline.Cpp as C C.context C.cppCtx C.include "pylon/PylonIncludes.h" C.include "iostream" C.using "namespace Pylon"; C.using "namespace std"; main :: IO () main = [C.block| void { PylonAutoInitTerm pylon; CInstantCamera camera( CTlFactory::GetInstance().CreateFirstDevice()); camera.RegisterConfiguration( (CConfigurationEventHandler*) NULL, RegistrationMode_ReplaceAll, Cleanup_None); cout << "Using device " << camera.GetDeviceInfo().GetModelName() << endl; }|] However, when the resulting executable is ran, it hangs - failing to print "Using device". inline-c generates a Test.cpp file, which contains #include "pylon/PylonIncludes.h" #include "iostream" using namespace Pylon; using namespace std; extern "C" { void inline_c_Main_0_e23f0c6a0bc10367be76252744bf4e6c74493314() { PylonAutoInitTerm pylon; CInstantCamera camera( CTlFactory::GetInstance().CreateFirstDevice()); camera.RegisterConfiguration( (CConfigurationEventHandler*) NULL, RegistrationMode_ReplaceAll, Cleanup_None); cout << "Using device " << camera.GetDeviceInfo().GetModelName() << endl; } } If I modify this exact file, I can turn it into something that can be run, by simply adding: int main() { inline_c_Main_0_e23f0c6a0bc10367be76252744bf4e6c74493314(); } At this point, I can now compile that very C++ code with G++ and run it: [nix-shell:~/work/circuithub/receiving-station]$ g++ Test.cpp -I/home/ollie/work/circuithub/receiving-station/pylon5/include -L/home/ollie/work/circuithub/receiving-station/pylon5/lib64 -Wl,-E -lpylonbase -lpylonu tility -lGenApi_gcc_v3_0_Basler_pylon_v5_0 -lGCBase_gcc_v3_0_Basler_pylon_v5_0 -Wl,--enable-new-dtags -Wl,-rpath,/home/ollie/work/circuithub/receiving-station/pylon5/lib64 [nix-shell:~/work/circuithub/receiving-station]$ ./a.out GetDeviceDiscoveryInfo: bFunctionClass = 14, bFunctionSubClass = 3, bFunctionProtocol = 0. Device is not an U3V device. GetDeviceDiscoveryInfo: bFunctionClass = 14, bFunctionSubClass = 3, bFunctionProtocol = 0. Device is not an U3V device. Using device acA3800-14um So as we can see, the C++ code is not the problem. Does anyone know why I don't see the same behaviour from my Haskell application? I imagine there might be some thread trickery happening behind the scenes, but I don't know what to even begin looking for. Thanks, let me know if you need any more information. - Ollie

2 1

Re: [Haskell-cafe] library for set of heterogeneous values?
by Anthony Clayden 15 Aug '16

15 Aug '16

> Frames - http://acowley.github.io/Frames/ - is built on > top of vinyl and provides one way to access data either as > an array of structures or a structures of arrays. Thanks Doug, Nice ability to define column types on the fly, and interpret them from incoming CSV. Yes and treat as structure of arrays. AFAICT Frames keeps each set of records distinct; and wants each set to be same type/same columns and types. So there's no heterogeneous repository. > whether it allows the kind of filtering you were asking for. There's standard filtering features you'd get with Set or List. I'm not seeing any ability to match/join across different datasets. That is, you'd have to write your own code. AntC

1 0

Unable to correctly infer function type, via pattern matching?
by David Banas 15 Aug '16

15 Aug '16

Hi all, I wonder if anyone can help me find my error, in this code: It’s note clear to me why x :: a is an error, except that maybe the type of f is not being correctly inferred? Am I, maybe, not allowed to use pattern matching, on the right side of ‘=‘? Thanks, -db data Stream a = Cons a (Stream a) newtype StreamMap a b = SM (Stream a -> Stream b) instance Arrow StreamMap where pure f = SM g where g (Cons x xs) = Cons (f x) (g xs) SM f >>> SM g = SM (g . f) first (SM g) = SM h -- h :: Stream (a, c) -> Stream (b, c) where h :: Stream (a, c) -> Stream (b, c) h (Cons (x, y) zs) = Cons ((f x), y) (h zs) g :: Stream a -> Stream b g (Cons x xs) = Cons (f x) (g xs) Couldn't match expected type ‘b1’ with actual type ‘a’ ‘a’ is a rigid type variable bound by the type signature for g :: interactive:IHaskell152.Stream a -> interactive:IHaskell152.Stream b1 at :10:17 ‘b1’ is a rigid type variable bound by the type signature for g :: interactive:IHaskell152.Stream a -> interactive:IHaskell152.Stream b1 at :10:17 Relevant bindings include xs :: interactive:IHaskell152.Stream a (bound at :11:27) x :: a (bound at :11:20) g :: interactive:IHaskell152.Stream a -> interactive:IHaskell152.Stream b1 (bound at :11:12) In the first argument of ‘f’, namely ‘x’ In the first argument of ‘IHaskell152.Cons’, namely ‘(f x)’

2 1

Re: [Haskell-cafe] Twitter coding kata
by Damian 14 Aug '16

14 Aug '16

I don't know about the feed, but a while ago I was playing with some exercises at exercism.io. Maybe you'd find it interesting. Regards, Damian Op 14 aug. 2016 21:30 schreef "Michael Litchard" <michael(a)schmong.org>: I've been told that there is a twitter feed that gives out little haskell exercises. Can't find it. Anyone know about it? _______________________________________________ Haskell-Cafe mailing list To (un)subscribe, modify options or view archives go to: http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe Only members subscribed via the mailman list are allowed to post.

4 3

Twitter coding kata
by Michael Litchard 14 Aug '16

14 Aug '16

I've been told that there is a twitter feed that gives out little haskell exercises. Can't find it. Anyone know about it?

1 0

Function and pattern bindings
by James Brown 14 Aug '16

14 Aug '16

I am reading Haskell report 2010 and I can't understand the differences between function bindings and pattern bindings. Can anyone explain the differences?

2 1

The relationship between F-algebras and the Free Monad
by William Yager 14 Aug '16

14 Aug '16

Hello all, I recently read the article "Understanding F-algebras"[1], which goes over the usage of F-algebras for e.g. evaluating ASTs. This article goes over how 1. Data.Fix creates the initial F-algebra over a functor f. 2. We can express our AST as a non-recursive functor instead of a recursive type 3. We can express our evaluator as an Algebra (of the type `f a -> a`, where f is the type of our AST and `a` is the Algebra's carrier type, i.e. our result type) 4. We can express terms in our language as members of the type `Fix AST` (i.e. the initial F-algebra over our AST). 5. By using a catamorphism over our evaluator algebra, we can easily construct an efficient evaluator. As a brief example of these principles, see the following program (using DeriveFunctor): data AST a = Lit Int | Add a a deriving Functor -- data Fix f = Fix (f (Fix f)) -- defined in Data.Fix type AST' = Fix AST program :: AST' program = Fix $ Add (Fix $ Lit 5) (Fix $ Lit 4) alg :: AST Int -> Int alg (Lit i) = i alg (Add l r) = l + r eval :: AST' -> Int eval = Data.Fix.cata alg main = print $ eval program This is super cool! One thing that stood out to me is that there are a number of similarities here with the usage of the Free Monad. In particular, see "Why free monads matter" [2]. This article is doing basically the exact same thing. You express your AST as a non-recursive functor parametrized over the type of subterms. However, instead of making your terms of type `Fix AST`, they are of type `Free AST a`. Now, the recursive constructor for Free is almost identical to the constructor for Fix, except of course the additional type parameter `a`. However, both types are of the form `data T = R (f T)`. Free simply has the additional `Pure` constructor as well. So obviously, there is some sort of relationship here. However, I don't have a good enough grasp on these concepts for the relationship to make itself fully apparent. Some things I've noticed: Operations on `Fix AST` terminate because the AST type has leaf constructors without recursion. So a catamorphism over an evaluation algebra can plausibly terminate because eventually it will hit a leaf node and the evaluation will stop. On the other hand, operations on `Free AST a` can also terminate because you might run into a `Pure` constructor. The difference being that `Pure` is a part of the wrapper type (Free) and not the wrapped type (AST). A practical question I have is: Can we use the Free Monad to write AST terms using `do` notation (useful for DSLs) and then use the elegant catamorphism evaluator trick (or something similar) to evaluate our ASTs? Or does evaluating the Free Monad require something more general due to the Pure constructor? It looks like `Control.Monad.Free.iter` might be equivalent to `Data.Fix.cata`, but I'm not sure. It looks like a rough translation works in this case: data AST a = Add a a deriving Functor -- No more "Const" type AST' a = Free AST a program :: AST' Int program = Free $ Add (Pure 5) (Pure 4) alg :: AST Int -> Int alg (Add l r) = l + r eval :: AST' Int -> Int eval = Control.Monad.Free.iter alg main = print $ eval program So, intuitively, it seems like Free lets us do basically the same thing as Fix but with the evaluation result present as the last argument of the expression type. Sorry for being a bit rambly, and I may also be completely off base here, so correct me if I'm not making any sense. Cheers, Will [1] https://www.schoolofhaskell.com/user/bartosz/understanding-algebras [2] http://www.haskellforall.com/2012/06/you-could-have-invented-free-monads.ht…

1 0

(job) haskell software engineer for autopilot/simulation environment
by Greg Horn 13 Aug '16

13 Aug '16

We are a small, fast moving R&D group in Kitty Hawk <https://kittyhawk.aero/> writing autopilots in Haskell and code-generating to C. The ground station and simulation environment are written almost entirely in Haskell, and are mostly open-source. We are currently flight testing a few different novel vehicles. We're looking for an experienced software engineer familiar with simulation and control of dynamic systems, real-time systems, robotics, or similar. The role is initially to support and expand the existing simulation and control infrastructure, but will be flexible based on your interests and expertise. If this is interesting to you, please see the full description at: https://jobs.lever.co/kittyhawk.aero/89a6630b-4210-4a4a-89d8-936d458f6c8a?l… Best regards, Greg

1 0

Re: [Haskell-cafe] library for set of heterogeneous values?
by Anthony Clayden 13 Aug '16

13 Aug '16

> I don't know if they're at all suitable for your purposes, > but you should look (at least for inspiration) at both > vinyl and dependent-map. Thanks David, vinyl is a record 'solution', not a set-of-records repository Really there's now too many bewildering choices for records; representing the records is not the difficult part. dependent-map, and vault [Heinrich Apfelmus,thank you Sergei for the suggestion] seem to be (key, value) stores so I'm not seeing how I 'query'/filter the values (the whole records) if I don't already know the keys for those records. Contrast that with Data.Set [*], you could stream the contents to a list and filter. (Which would be horribly inefficient for my purposes.) [*] Data.Set seems to have been swallowed into the new collections library, which is not currently maintained :-( AntC

2 1

Need an example of new type constructor with zero data constructors
by James Brown 12 Aug '16

12 Aug '16

In the Haskell report 2010, a data declaration has the format of: <https://lh3.googleusercontent.com/-G-z92n-50B0/V63XKCCrJDI/AAAAAAAAAGA/w-Zd…> For a new type, there could be zero or more data constructors. What's the use case for a new type that has zero data constructor?

6 8

Hac φ: a Haskell Exchange in Philadelphia, Oct 21–23
by Richard Eisenberg 12 Aug '16

12 Aug '16

Hac Phi, a yearly weekend of Haskell in Philadelphia, will take place Oct. 21–23, 2016, at the University of Pennsylvania. Hac Phi is a gathering of hackers and Haskell enthusiasts. Come bring a project you’re working on or offer to help someone else on a project of theirs. Come give a talk if you’ve got something to share. Come to learn something new. What do we mean by a “Haskell Exchange”? Less pressurized than a hackathon, more informal than a conference, bigger than a meetup – Hac Phi is a weekend where academics, professionals, and hobbyists can all meet, mingle, hack on each others’ projects, and generally have a good time. (And it’s not to be confused with *the* Haskell eXchange, an entirely different event.) All the details are on [the wiki page](https://wiki.haskell.org/Hac_Phi); please [register online](https://goo.gl/forms/XXTxKFYAryVTjlgo2 <https://goo.gl/forms/XXTxKFYAryVTjlgo2>) if you’re coming. We hope to see you there! —The Hac φ team Antal Spector-Zabusky Kenny Foner

1 0

When you don't want to restrict the type of array...
by Christopher Howard 12 Aug '16

12 Aug '16

Hi. I recently learned how to use Haskell IArrays and MArrays, and they are quite convenient. I find myself often using some type of MArray for performance reasons, but also some IArray type for array data that is static in a set of computations. Then I started wanting to use arrays inside other kinds of data types, and so quickly ran into the question: what do you do if you want a data type to contain an array, but you don't know in advance what array type you'll be working with (immutable vs. mutible, boxed vs. unboxed). My exploration of this question led to discovering something called GADTs, which allowed me to do definitions like so data Surface a where ISurface :: IArray a e => (a Int Vertex) -> (a Int Face) -> Surface a MSurface :: MArray a e m => (a Int Vertex) -> (a Int Face) -> Surface a Am I heading down the right track here, or is there some better approach? -- https://qlfiles.net My PGP public key ID is 0x340EA95A (pgp.mit.edu)

2 1

Read lines of a file into a Vector
by Jake 11 Aug '16

11 Aug '16

I want to write a function that will read the contents of a file and return a Vector of its lines: readLines :: Handle -> IO (Vector String) I have an implementation that works but seems to naive and inefficient to me because it reads the entire file contents, *then *splits it into lines, and *then* converts it to a Vector from a list. readLines h = fromList . lines <$> hGetContents h I would like to a) use hGetLine and continue until I get an isEOFError and b) read directly into a Vector instead of a list. I started something using Data.Vector.unfoldr but I the presence of the IO monad around my String was causing issues I couldn't figure out how to solve. I'd also be curious to see how to do either one of these things separately and I assume they'd each help make my program more efficient on their own. Or, maybe my implementation is not as terrible as I thought because some laziness/fusion/optimization magic is happening behind the scenes? Thanks, Jake Waksbaum

3 2

[ANN] normalization-insensitive-2.0
by Patrick Pelletier 09 Aug '16

09 Aug '16

normalization-insensitive is identical to case-insensitive, except it is insensitive to Unicode normalization, rather than case. The module Data.Unicode.NormalizationInsensitive provides the NI type constructor which can be parameterized by a string-like type like: String, ByteString, Text, etc.. Comparisons of values of the resulting type will be insensitive to normalization. https://hackage.haskell.org/package/normalization-insensitive https://github.com/ppelleti/normalization-insensitive I created this to solve a problem I was running into comparing filenames on Mac OS X. Because Mac OS X converts all filenames to Normalization Form D, the filenames I read back from disk were different than the filenames I had written to disk. This package solved the problem very neatly. Under the hood, normalization-insensitive uses the unicode-transforms package, which Harendra Kumar announced a few days ago on haskell-cafe. This avoids having to pull in any heavyweight dependencies like ICU. Thanks to Bas van Dijk for writing case-insensitive, upon which normalization-insensitive is based. And thanks for Harendra Kumar for reviewing normalization-insensitive and providing feedback, as well as writing unicode-transforms. Although this is the first release of normalization-insensitive, the version number is 2.0 to avoid any confusion with the version numbers of case-insensitive. --Patrick

1 0

Re: [Haskell-cafe] Suggestions for an empirical master thesis
by Doug McIlroy 08 Aug '16

08 Aug '16

>The number of bugs would have to be normalized using the numbers of users of a project (maybe measured in number of downloads). Do you expect more bugs for frequently downloaded packages, or fewer downloads for packages with many bug reports or bug rate diminishing with downloads? It's a slippery topic. Doug

3 2

Re: [Haskell-cafe] Suggestions for an empirical master thesis
by Doug McIlroy 06 Aug '16

06 Aug '16

> >The number of bugs would have to be normalized using the numbers of users of a project (maybe measured in number of downloads).

1 0

Comparable Haskell text(s) to "ML for the Working Programmer"?
by Lawrence Bottorff 06 Aug '16

06 Aug '16

Is there a book or books that cover as much, as well as the Lawrence Paulson "ML for the Working Programmer (2nd ed)" for Haskell? What I'd like in Haskell form is pretty much exactly what Paulson covers in his brilliant book. LB

3 2

a wiki in yesod package
by Ruben Astudillo 06 Aug '16

06 Aug '16

Hi all I've been looking for a package or helpful material to do a wiki based on yesod. I seen the example on the book[1] and thought maybe somebody published something. by the way: which is the mailing list of yesod? the haskell-web is really silent. [1]: http://www.yesodweb.com/book/wiki-chat-example -- -- Ruben Astudillo

2 1

Design Question - Functions taking 'subtype' like arguments but has to be restricted to one type
by Gurudev Devanla 06 Aug '16

06 Aug '16

Hello All, I have a design question where I could use some of your thoughts and suggestions. Here is the setup. I apologize for the long email but I have resisted asking this question, since it needs a long explanation, until now. I have a set of data structures defined as follows -- An Item that can be of two types, one whose value can be changed, one whose value are frozen once created data Item = FreeToChange {freeToChangeCount:: Int} | CannotChange {frozenCount:: Int} -- The item is part of a basket data Basket = Basket { name:: String, item::Item } -- The cart can have both kind of Baskets at the start of the program, or during runtime. data Cart = List Basket You can imagine this be a shopping cart with fixed set of items. Where the count of some of the items in the basket can be changed during shopping but not the count of the items once they are tagged as frozen. Therefore, valid operation are: 1. I can create an Basket with either FreeToChange item or CannotChange item. 2. I can update the count for FreeToChange item in the Basket 3. But, once I create an instance of the Basket to contain the CannotChange item, we cannot update the count anymore or update the Basket. One approach I have taken is to throw an error if this happens by pattern matching on type. But, this is an runtime check. addToBasket :: Basket -> Basket addToBasket b = let i = item b i' = case i of FreeToChange f -> FreeToChange {freeToChangeCount = f + 1} CannotChange f -> error ("This operation is not allowed") in b {item=i'} Here are my questions: 1. Is there a way to design the above data structures in such a way I could use the type system. 2. Since, these are runtime changes, is it even a good design pattern to push this responsibility to a type system? Thanks Guru

7 11

Suggestions for an empirical master thesis
by Jon Kristensen 06 Aug '16

06 Aug '16

Hi, everyone! I'm looking for a master thesis topic that is empirical in nature (like, statistics, hypothesis testing, etc.). The work could involve analyzing either package metadata (Cabal information), code (AST), and/or data from some other source, possibly comparing similar data from some non-Haskell domain. As an example, one idea that was suggested to me was to look at usage aggregation, or like, how much of a given package another package is actually using (which could be relevant in any orphan-instance discussion). From an academic standpoint, it would be good to pick a metric that can be validated in some way. Thank you! Best, Jon

3 3

Views of data types
by Corentin Dupont 04 Aug '16

04 Aug '16

Hi guys, I have a typeclass like that: class Signal s where type SignalData s :: * The idea is that when some signal "s" fires, it returns a data of type (SignalData s). This is all fine except when I instantiate the class with: data Input a = Input [(a, String)] instance Signal (Input a) type SignalData (Input a) = a The concrete type of Input a is not known, so its difficult to store in lists, to serialize... So I need to create a "view" for the it: class (Signal s, Signal v) => SignalView s v where view :: s -> v data InputView = InputView [(Int, String)] instance Signal InputView type SignalData InputView = Int instance SignalView (Input a) InputView view (Input as) = InputView (zip [0…] (snd <$> as)) Is this a common pattern? I'm not sure I get it right...

2 1

[ANN] Compose :: Melbourne 2016 Speakers!
by Lyndon Maydwell 04 Aug '16

04 Aug '16

Hello Everyone! In case you haven't heard, Compose :: Melbourne (the new sister-conference of Compose) has now announced its program of presentations for the first day: http://www.composeconference.org/2016-melbourne/day-one-program/ Compose is a conference for functional programmers, focused on technologies such as Haskell, Scala, Clojure, OCaml, F#, SML and others. Compose :: Melbourne will run on the 29th and 30th of August (this month!) We're excited to have a wide range of talks on a diverse selection of topics including an opening keynote by Manuel M.T. Chakravarty (the author of Haskell for Mac). There will be a single track of 10 speakers from Melbourne, Australia, and around the world! ## Unconference and Workshops The second day of the conference will take the form of an unconference. The day will also feature a collection of organised, as well as spontaneous workshops including introductions to Haskell and Purescript: http://www.composeconference.org/2016-melbourne/unconference/ ## Financial Assistance If you need help attending Compose :: Melbourne, then contact us. We have put in place a financial-assistance plan: http://www.composeconference.org/2016-melbourne/assistance/ ## Volunteering As Compose :: Melbourne will be running in just a few short weeks, we're currently looking for volunteers to help assist with running the workshops on day-two. If you feel like lending a hand, then don't hesitate to get in touch! ## Sponsorship If you, or your organisation wishes to lend assistance to Compose :: Melbourne, we are accepting sponsorship. If you want to learn more, then please view our sponsorship-prospectus: https://github.com/composeconference/Compose-Melbourne/wiki/Sponsorship-Tie… ## Getting in Touch To get in touch with the organisers of Compose :: Melbourne, then email the committee at <composemel-admin(a)googlegroups.com>. For more information, see the home-page of Compose Conference: http://www.composeconference.org/

1 0

memory usage: general questions
by Christopher Howard 04 Aug '16

04 Aug '16

Hi. I've spent the last few days reading about strictness, non-strictness, laziness, thunks, and persistence, and to be honest I'm still in a bit of a fog. A few questions, which I hope might help me out: Supposing I have an expression f (f (f b))) where f :: B -> B and B is some ginormous persistent data structure. and f is an "updating" function outputting some modified copy version of it's argument So, a few questions: 1) Supposing that f does not short-circuit: Is it correct to say that it is definitely advantageous (from a memory usage perspective) for f to be a strict function? Or is this heavily dependent on whether or not b contains unevaluated data structures (e.g., a list)? 2) As far as the overall peak size of our memory graph: How will it be affected by the size of b, if f is non-strict? and if f is strict? 3) Are the "overwritten" portions of each B (i.e., those parts of the persistent data we no are no longer needed) guaranteed to be pushed out of memory at any particular point? Is this something we know will (might?) happen as soon as the GC is run? Or does it happen right when each f is applied to it's argument? -- https://qlfiles.net To protect my privacy, please use PGP encryption. It's free and easy to use! My public key ID is 0x340EA95A (pgp.mit.edu)

3 3

ANN: unicode-transforms-0.1.0.1 (unicode normalization)
by Harendra Kumar 04 Aug '16

04 Aug '16

This is for those who want unicode normalization but do not want a dependency on the heavyweight icu libraries. It has the same API as the text-icu package. It is based on the utf8proc C implementation. https://hackage.haskell.org/package/unicode-transforms https://github.com/harendra-kumar/unicode-transforms A pure Haskell implementation is a work in progress, it works for the NFD normalization form as of now. I could make it perform better than the current utf8proc C implementation and it even beats the ICU implementation in one of the benchmarks. I intend to finish it when I find time to work on it again. Contributions are welcome! -harendra

1 0

[Job] Formal Tech is hiring
by Iavor Diatchki 03 Aug '16

03 Aug '16

Hello, Formal Tech, a Galois spin-off, is looking for a mid to senior level engineer to work on CyberChaff ( https://formal.tech/products/cyberchaff/) Applicants should be proficient in Haskell and at least one other programming language. This is a full time position with benefits. If you are interested, please send your resume to careers(a)formal.tech Cheers, -Iavor

1 0

Measuring allocations with 'weigh' - what about thunks?
by Mitchell Rosen 03 Aug '16

03 Aug '16

weigh (https://www.fpcomplete.com/blog/2016/05/weigh-package) is a library measures how much allocation evaluating a function causes. It's basically a nice interface to GHC.Stats.getGCStats. Here is an example that measures *\n -> n+1*: import Weigh main :: IO () main = mainWith (func "+1" plusOne 5) plusOne :: Int -> Int plusOne = \n -> n + 1 which prints Case Bytes GCs Check +1 16 0 OK when run (64 bit machine; allocating 1 Int = 16 bytes). So my question is, what about the thunk allocated by *(+)*? My rough understanding of the heap is this: Code Heap ---- ---- 1 1 1 1 1 plusOne 1 +-------+----------+----+ +----+---+ | THUNK | reserved | --|--> | I# | 5 | +-------+----------+----+ +----+---+ 1 1 1 1 1 deepseq it +-------+----------+----+ +----+---+ | IND | | --|--> | I# | 5 | +-------+-----|----+----+ +----+---+ | 1 1 `------------> +----+---+ | I# | 6 | +----+---+ 1 1 GC +----+---+ | I# | 6 | +----+---+ So haven't we allocated 5 bytes, not two? Three for the GC'd thunk, and two for the new Int? Any clarification or pointers (heh) to some GHC reading would be greatly appreciated! Thanks, Mitchell

1 0

[ANN] HaRe 0.8.3.0 Released
by Alan & Kim Zimmerman 03 Aug '16

03 Aug '16

Now that ghc-mod 5.6.0.0 is out, I have been able to release HaRe for GHC 8.0.1 There are no functional changes, this release just adds support for GHC 8.0.1. Just a heads up for anyone who is interested, my plans for the near future are 1. Complete adding default annotations to ghc-exactprint. This will allow pretty printing a GHC AST that has been generated via some process other than parsing source, by adding annotations to it. 2. Return to haskell-ide-engine The initial focus will be on enabling the remote ghci mode into it. In general, my focus is on improving the tooling experience around GHC. Alan

1 0

What's the state of programming on the Xeon Phi with Haskell?
by Jules Mazur 02 Aug '16

02 Aug '16

I recently gained access to a Xeon Phi (Knights Corner edition, a bit dated but useful to play around with), and I'm interested in using Haskell to program for the Phi platform. Sadly, the only lead I've got about working with both technologies is a 2014 paper by Liu, et al. at Intel Research (available via [this site](https://www.researchgate.net/publication/262310691_The_Intel_Labs_Has…) In a 3-month-old [Reddit thread](https://www.reddit.com/r/haskell/comments/4hokvy/is_there_any_way_t…, one of the authors mentions that the compiler may be released at a future date, but implied that it will likely have some degree of instability. Are there any libraries or compilers, or even extensions or modifications for GHC or other existing compilers, that allow compilation for the Xeon Phi?

1 0

ANN: haskell-src-exts-simple
by Bertram Felgenhauer 02 Aug '16

02 Aug '16

Dear all, I've just released haskell-src-exts-simple 1.18.0.0 on hackage [1]. (This is the first release. The first two components of the version follow haskell-src-exts.) >From the README: This package provides a shim for haskell-src-exts, exposing the same AST but without annotations. This package is useful for synthesizing and manipulating HSE ASTs that don't carry source location information. It may also aid in porting packages from haskell-src-exts 1.17 to 1.18, but it is not a drop-in replacement for the old annotation-free AST. See [2] for details. Happy hacking, Bertram [1] https://hackage.haskell.org/package/haskell-src-exts-simple [2] https://github.com/int-e/haskell-src-exts-simple/blob/master/COMPATIBILITY.…

1 1

Haskell in Leipzig 2016: Call for Participation
by Joachim Breitner 02 Aug '16

02 Aug '16

Haskell in Leipzig September 14-15, 2016 HTKW Leipzig, Germany http://hal2016.haskell.org/ We have received many interesting submissions for HAL and were able to assemble a great program, which you can find here: http://hal2016.haskell.org/program.html Abstracts and final schedule will be added soonish™. As you can see, we have an interesting program spanning from practical, real-word uses of Haskell over data structures and libraries to game- and music programming. Besides the 12 talks, there are three tutorials to attend. As a special treat, on the evening of September 14, Anton Kholomiov will give a live music coding performance! If you are interested in attending, please head over to http://nfa.imn.htwk-leipzig.de/LDEC2016/registration/ and follow the instructions. HAL is cheap, and even cheaper for students, and yet cheaper if you pay by the early registration deadline of August 15¹ Also check out the other two conferences of LDEC (WLP and WLFP), and if you like them, make it a week full of functional programming! Thanks, Joachim Breitner on behalf of the program committee ¹ Note that the early registration deadline is for the money, so make sure you allow for the bank to transfer it in time. -- Dr. rer. nat. Joachim Breitner Wissenschaftlicher Mitarbeiter http://pp.ipd.kit.edu/~breitner

1 0

PEPM 2017 Second Call for Papers
by Jeremy Yallop 02 Aug '16

02 Aug '16

SECOND CALL FOR PAPERS Workshop on PARTIAL EVALUATION AND PROGRAM MANIPULATION (PEPM 2017) NEWS: Keynote talk by Neil Jones, DIKU (see below). http://conf.researchr.org/home/PEPM-2017 Paris, France, January 16th - 17th, 2017 (co-located with POPL 2017) PEPM is the premier forum for discussion of semantics-based program manipulation. The first ACM SIGPLAN PEPM symposium took place in 1991, and meetings have been held in affiliation with POPL every year since 2006. PEPM 2017 will be based on a broad interpretation of semantics-based program manipulation, reflecting the expanded scope of PEPM in recent years beyond the traditionally covered areas of partial evaluation and specialization. Specifically, PEPM 2017 will include practical applications of program transformations such as refactoring tools, and practical implementation techniques such as rule-based transformation systems. In addition, the scope of PEPM covers manipulation and transformations of program and system representations such as structural and semantic models that occur in the context of model-driven development. In order to maintain the dynamic and interactive nature of PEPM and to encourage participation by practitioners, we also solicit submissions of short papers, including tool demonstrations, and of posters. Scope ----- Topics of interest for PEPM 2017 include, but are not limited to: * Program and model manipulation techniques such as: supercompilation, partial evaluation, fusion, on-the-fly program adaptation, active libraries, program inversion, slicing, symbolic execution, refactoring, decompilation, and obfuscation. * Program analysis techniques that are used to drive program/model manipulation such as: abstract interpretation, termination checking, binding-time analysis, constraint solving, type systems, automated testing and test case generation. * Techniques that treat programs/models as data objects including metaprogramming, generative programming, embedded domain-specific languages, program synthesis by sketching and inductive programming, staged computation, and model-driven program generation and transformation. * Application of the above techniques including case studies of program manipulation in real-world (industrial, open-source) projects and software development processes, descriptions of robust tools capable of effectively handling realistic applications, benchmarking. Examples of application domains include legacy program understanding and transformation, DSL implementations, visual languages and end-user programming, scientific computing, middleware frameworks and infrastructure needed for distributed and web-based applications, embedded and resource-limited computation, and security. This list of categories is not exhaustive, and we encourage submissions describing applications of semantics-based program manipulation techniques in new domains. If you have a question as to whether a potential submission is within the scope of the workshop, please contact the programme chairs. Submission categories and guidelines ------------------------------------ Three kinds of submissions will be accepted: Regular Research Papers, Short Papers and Posters. * Regular Research Papers should describe new results, and will be judged on originality, correctness, significance and clarity. Regular research papers must not exceed 12 pages in ACM Proceedings style (including appendix). * Short Papers may include tool demonstrations and presentations of exciting if not fully polished research, and of interesting academic, industrial and open-source applications that are new or unfamiliar. Short papers must not exceed 6 pages in ACM Proceedings style (including appendix). * Posters should describe work relevant to the PEPM community, and must not exceed 2 pages in ACM Proceedings style. We invite poster submissions that present early work not yet ready for submission to a conference or journal, identify new research problems, showcase tools and technologies developed by the author(s), or describe student research projects. At least one author of each accepted contribution must attend the workshop and present the work. In the case of tool demonstration papers, a live demonstration of the described tool is expected. Suggested topics, evaluation criteria, and writing guidelines for both research tool demonstration papers will be made available on the PEPM 2017 web site. Student participants with accepted papers can apply for a SIGPLAN PAC grant to help cover travel expenses and other support. PAC also offers other support, such as for child-care expenses during the meeting or for travel costs for companions of SIGPLAN members with physical disabilities, as well as for travel from locations outside of North America and Europe. For details on the PAC programme, see its web page. Publication and special issue ----------------------------- All accepted papers, short papers and posters included, will appear in formal proceedings published by ACM Press. Accepted papers will be included in the ACM Digital Library. Authors of selected papers from PEPM 2016 and PEPM 2017 will also be invited to expand their papers for publication in a special issue of the journal Computer Languages, Systems and Structures (COMLAN, Elsevier). Keynote ------- Neil Jones (DIKU) will give the PEPM keynote talk, titled Compiling Untyped Lambda Calculus to Lower-level Code by Game Semantics and Partial Evaluation Best paper award ---------------- PEPM 2017 continues the tradition of a Best Paper award. The winner will be announced at the workshop. Submission ---------- Papers should be submitted electronically via HotCRP. https://pepm17.hotcrp.com/ Authors using LaTeX to prepare their submissions should use the new improved SIGPLAN proceedings style, and specifically the sigplanconf.cls 9pt template. Important Dates --------------- For Regular Research Papers and Short Papers: * Abstract submission : Tuesday 13th September 2016 * Paper submission : Friday 16th September 2016 * Author notification : Monday 24th October 2016 * Camera ready : Monday 28th November 2016 For Posters: * Poster submission : Sunday 30th October 2016 * Author notification : Friday 10th November 2016 * Camera ready : Monday 28th November 2016 PEPM workshop: * Workshop : Monday 16th - Tuesday 17th January 2017 The proceedings will be published 2 weeks pre-conference. AUTHORS TAKE NOTE: The official publication date is the date the proceedings are made available in the ACM Digital Library. This date may be up to two weeks prior to the first day of your conference. The official publication date affects the deadline for any patent filings related to published work. (For those rare conferences whose proceedings are published in the ACM Digital Library after the conference is over, the official publication date remains the first day of the conference.). PEPM'17 Programme Committee --------------------------- Elvira Albert (Complutense University of Madrid, Spain) Don Batory (University of Texas at Austin, USA) Martin Berger (University of Sussex, UK) Sebastian Erdweg (TU Delft, Netherlands) Andrew Farmer (Facebook, USA) Matthew Flatt (University of Utah, USA) John Gallagher (Roskilde University, Denmark) Robert Glück (DIKU, Denmark) Jurriaan Hage (Utrecht University, Netherlands) Zhenjiang Hu (National Institute of Informatics, Japan) Yukiyoshi Kameyama (University of Tsukuba, Japan) Ilya Klyuchnikov (Facebook, UK) Huiqing Li (EE, UK) Annie Liu (Stony Brook University, USA) Markus Püschel (ETH Zurich, Switzerland) Ryosuke SATO (University of Tokyo, Japan) Sven-Bodo Scholz (Heriot-Watt University, UK) Ulrik Schultz (co-chair) (University of Southern Denmark) Ilya Sergey (University College London, UK) Chung-chieh Shan (Indiana University, USA) Tijs van der Storm (Centrum Wiskunde & Informatica, Netherlands) Jeremy Yallop (co-chair) (University of Cambridge, UK)

1 0

FINAL CALL FOR TALKS (Aug 8 deadline): Haskell Implementors Workshop 2016, Sep 24, Nara
by Edward Z. Yang 01 Aug '16

01 Aug '16

Deadline is in a week! Submit your talks! Call for Contributions ACM SIGPLAN Haskell Implementors' Workshop http://haskell.org/haskellwiki/HaskellImplementorsWorkshop/2016 Nara, Japan, 24 September, 2016 Co-located with ICFP 2016 http://www.icfpconference.org/icfp2016/ Important dates --------------- Proposal Deadline: Monday, 8 August, 2016 Notification: Monday, 22 August, 2016 Workshop: Saturday, 24 September, 2016 The 8th Haskell Implementors' Workshop is to be held alongside ICFP 2016 this year in Nara. It is a forum for people involved in the design and development of Haskell implementations, tools, libraries, and supporting infrastructure, to share their work and discuss future directions and collaborations with others. Talks and/or demos are proposed by submitting an abstract, and selected by a small program committee. There will be no published proceedings; the workshop will be informal and interactive, with a flexible timetable and plenty of room for ad-hoc discussion, demos, and impromptu short talks. Scope and target audience ------------------------- It is important to distinguish the Haskell Implementors' Workshop from the Haskell Symposium which is also co-located with ICFP 2016. The Haskell Symposium is for the publication of Haskell-related research. In contrast, the Haskell Implementors' Workshop will have no proceedings -- although we will aim to make talk videos, slides and presented data available with the consent of the speakers. In the Haskell Implementors' Workshop, we hope to study the underlying technology. We want to bring together anyone interested in the nitty-gritty details behind turning plain-text source code into a deployed product. Having said that, members of the wider Haskell community are more than welcome to attend the workshop -- we need your feedback to keep the Haskell ecosystem thriving. The scope covers any of the following topics. There may be some topics that people feel we've missed, so by all means submit a proposal even if it doesn't fit exactly into one of these buckets: * Compilation techniques * Language features and extensions * Type system implementation * Concurrency and parallelism: language design and implementation * Performance, optimisation and benchmarking * Virtual machines and run-time systems * Libraries and tools for development or deployment Talks ----- At this stage we would like to invite proposals from potential speakers for talks and demonstrations. We are aiming for 20 minute talks with 10 minutes for questions and changeovers. We want to hear from people writing compilers, tools, or libraries, people with cool ideas for directions in which we should take the platform, proposals for new features to be implemented, and half-baked crazy ideas. Please submit a talk title and abstract of no more than 300 words. Submissions should be made via HotCRP. The website is: https://icfp-hiw16.hotcrp.com/ We will also have a lightning talks session which will be organised on the day. These talks will be 5-10 minutes, depending on available time. Suggested topics for lightning talks are to present a single idea, a work-in-progress project, a problem to intrigue and perplex Haskell implementors, or simply to ask for feedback and collaborators. Organisers --- End forwarded message ---

1 0

Re: [Haskell-cafe] [ANN] hgmp-0.1.0.0
by Claude Heiland-Allen 01 Aug '16

01 Aug '16

Hi Sergey, café, On 01/08/16 21:13, Sergey Bushnyak wrote: > Nice work! How it differs from > https://hackage.haskell.org/package/integer-gmp ? Good question! integer-gmp is a binding of enough of GMP to make implementing Integer possible. It is very low level in the GHC package heirarchy, so trying to make it provide high level code is painful, if not impossible. It exposes the bare minimum of functionality to let most of Integer be implemented by the base package. hgmp uses the public integer-gmp internal details (also ghc-prim for the lower level stuff like copying byte arrays to/from Haskell heap / foreign memory) to expose helpers using Integer and Rational for interacting with foreign code that expects mpz_t and mpq_t data structures. So the package heirarchy is something like this diagram (fixed width font recommended): hgmp -- Integer and Rational FFI helpers for libgmp API / | \ | | base -- Integer numeric instances, the standard Prelude, etc | | | : | integer-gmp -- bindings for Integer implementation (bare minimum) | | / ghc-prim -- very low level compiler specifics hgmp eventually should also contain bindings to the functions in GMP, I'm considering the best way to go about it. My current thought is to generate raw and higher-level bindings semi-automatically from the C API header file gmp.h - any other suggestions? Claude > On 08/01/2016 10:57 PM, Claude Heiland-Allen wrote: >> Hi all, >> >> hgmp 0.1.0.0 is released! [0] >> >> hgmp is a Haskell interface to GMP[1] (for GHC with the default >> integer-gmp implementation of Integer). Contains type definitions and >> marshalling functions, to be able to write FFI bindings using >> Haskell's Integer and Rational types. Function bindings may come in a >> future version. >> >> A simple example illustrating binding to GMP's next probable-prime >> function: >> >> {-# LANGUAGE ForeignFunctionInterface #-} >> >> import Foreign.Ptr (Ptr(..)) >> import Numeric.GMP.Types (MPZ) >> import Numeric.GMP.Utils (withInInteger, withOutInteger_) >> import System.IO.Unsafe (unsafePerformIO) >> >> foreign import ccall safe "__gmpz_nextprime" >> mpz_nextprime :: Ptr MPZ -> Ptr MPZ -> IO () >> >> nextPrime :: Integer -> Integer >> nextPrime n = >> unsafePerformIO $ >> withOutInteger_ $ \rop -> >> withInInteger n $ \op -> >> mpz_nextprime rop op >> >> You can cabal install (or otherwise get it) from Hackage[2], or get >> (or browse[3]) the freshest sources from git: >> >> git clone https://code.mathr.co.uk/hgmp.git >> >> Any and all feedback welcome! I'm sure there are some things that >> could be improved, and ideas for future versions will be appreciated too. >> >> [0] https://mathr.co.uk/blog/2016-08-01_hgmp_0_1_0_0_released.html >> [1] https://gmplib.org/ >> [2] http://hackage.haskell.org/package/hgmp >> [3] https://code.mathr.co.uk/hgmp >> >> Thanks, >> >> >> Claude > -- https://mathr.co.uk

1 0

[ANN] hgmp-0.1.0.0
by Claude Heiland-Allen 01 Aug '16

01 Aug '16

Hi all, hgmp 0.1.0.0 is released! [0] hgmp is a Haskell interface to GMP[1] (for GHC with the default integer-gmp implementation of Integer). Contains type definitions and marshalling functions, to be able to write FFI bindings using Haskell's Integer and Rational types. Function bindings may come in a future version. A simple example illustrating binding to GMP's next probable-prime function: {-# LANGUAGE ForeignFunctionInterface #-} import Foreign.Ptr (Ptr(..)) import Numeric.GMP.Types (MPZ) import Numeric.GMP.Utils (withInInteger, withOutInteger_) import System.IO.Unsafe (unsafePerformIO) foreign import ccall safe "__gmpz_nextprime" mpz_nextprime :: Ptr MPZ -> Ptr MPZ -> IO () nextPrime :: Integer -> Integer nextPrime n = unsafePerformIO $ withOutInteger_ $ \rop -> withInInteger n $ \op -> mpz_nextprime rop op You can cabal install (or otherwise get it) from Hackage[2], or get (or browse[3]) the freshest sources from git: git clone https://code.mathr.co.uk/hgmp.git Any and all feedback welcome! I'm sure there are some things that could be improved, and ideas for future versions will be appreciated too. [0] https://mathr.co.uk/blog/2016-08-01_hgmp_0_1_0_0_released.html [1] https://gmplib.org/ [2] http://hackage.haskell.org/package/hgmp [3] https://code.mathr.co.uk/hgmp Thanks, Claude -- https://mathr.co.uk

1 0

[ANN] ghc-mod-5.6.0.0: Supporting GHC 8.0 and Cabal 1.24
by Daniel Gröber 01 Aug '16

01 Aug '16

I'm pleased to announce the release of ghc-mod 5.6.0.0! What's new? =========== * Support for GHC 8.0 and Cabal 1.24 Nothing too spectacular to report here, just regular maintenance work. * Type Contexts fixed Thanks to @Lierdakil `ghc-mod type` now finally displays type (class) constraints in most cases. This has been on the TODO list for a very long while now, going back to at least GHC 7.8. GHC's API just doesn't have a nice, simple, way for doing this and we had to resort to manually walking the typechecked AST while collecting constraints in various places. * Various bug fixes and smaller improvements From the change log: * Merge #737, `map-file` caching issues * Merge #767, Add `browse` option to show symbol "parents" * Fix #438, Case splitting not working * Fix #790, Don't try to use 'cabal' or 'stack' when it's not installed What is ghc-mod? ================ ghc-mod is both a back-end program for enhancing editors and other development environments with support for Haskell as well as a library for abstracting the black magic incantations required to use the GHC API in various environments, especially Cabal and Stack projects. The library is used by projects like HaRe[1], and haskell-ide-engine[2] Getting ghc-mod =============== GitHub: https://github.com/DanielG/ghc-mod Hackage: http://hackage.haskell.org/package/ghc-mod Editor frontends: - Emacs (native): https://github.com/DanielG/ghc-mod https://github.com/iquiw/company-ghc - Vim: https://github.com/eagletmt/ghcmod-vim https://github.com/eagletmt/neco-ghc - Atom: https://github.com/atom-haskell/ide-haskell Known issues ============ For issues other than the ones mentioned below visit our issue tracker: https://github.com/DanielG/ghc-mod/issues Frequently reported issues -------------------------- ghc-mod once compiled is bound to one version of GHC since we link against the GHC API library. This used to not be a very big problem but since Stack made it exceedingly easy for users to use more than one version of GHC without even knowing the number of problems in this area has exploded. We are tracing the issue in the following issue: https://github.com/DanielG/ghc-mod/issues/615 (Support switching GHC versions without recompiling ghc-mod) If you do notice any other problems please report them: https://github.com/DanielG/ghc-mod/issues/new ---- [1]: https://github.com/alanz/HaRe [2]: https://github.com/haskell/haskell-ide-engine

1 0

RFC: New version of haskell-src-exts without simplified AST
by Matthew Pickering 31 Jul '16

31 Jul '16

Dear all, For several months I have had a branch of haskell-src-exts which has been updated for all the new features in GHC 8. However, I have not yet released the changes as in this version I also removed the simplified AST. To those unfamiliar, HSE provides two ASTs, one which has source locations and one which doesn't. I have removed the one which doesn't. This simplifies maintenance and I think also makes the library easier to use. I have held back releasing this version as there are some people who use the simplified AST. The changes necessary for the new version are mechanical and easy to make. For example, David Fox updated haskell-names to use my branch [1] with few problems. The question is, are there any users of the library who object to this change? Matt [1]: https://github.com/haskell-suite/haskell-names/pull/73

3 7

Re: [Haskell-cafe] RFC: revisiting the simplified haskell-src-exts AST
by Matthew Pickering 31 Jul '16

31 Jul '16

Hello Bertram, This is a good idea. I also considered this but to provide a proper compatibility layer it is necessary to "bundle" pattern synonyms with suitable type constructors so that when users import the type constructor then they also import the suitable pattern synonyms. This feature was only implemented in GHC 8.0. It is currently not much effort to maintain HSE to support back to at least GHC 7.4 so it didn't seem worth sacrificing this. It would be good to provide this shim in future versions of the library but at the moment the feature isn't mature enough. Message me when you release this to Hackage and I will add a link to the README. Matt On Sat, Jul 30, 2016 at 11:22 PM, Bertram Felgenhauer via Haskell-Cafe < haskell-cafe(a)haskell.org> wrote: > Dear all, > > the latest major release of haskell-src-exts (version 1.18) removed > the annotation free variant of the Haskell AST. It occurred to me that > using ghc's pattern synonyms it is possible to offer a light-weight > simplified view on the annotated AST. For example, > Language.Haskell.Exts.Syntax defines > > data Name l = Ident l String | Symbol l String > > and we can provide a simplified view with all annotations equal to () > by doing > > {-# LANGUAGE PatternSynonyms #-} > import qualified Language.Haskell.Exts.Syntax as H > > type Name = H.Name () > pattern Ident a = H.Ident () a > pattern Symbol a = H.Symbol () a > > Because the type isn't changed, no code has to be reimplemented to > work with this AST. > > A first rough cut at an implementation can be found on github [1]. > Before releasing it on hackage (which requires some more polishing) > I'd appreciate feedback on the approach. Would you consider using > such a package? Is there a better approach? Also any thoughts on > usability (e.g., how to approach documentation) would be welcome. > > Cheers, Bertram > > [1] https://github.com/int-e/haskell-src-exts-simple > > > P.S. This grew out of an effort to update lambdabot to HSE-1.18, > which made me feel awful about all the superfluous and ugly () in > the resulting code. I also have some numbers showing that the > annotation-free view makes updating the code smoother: > > Using the annotation-free view, the update touches 75 lines: > src/Lambdabot/Plugin/Haskell/Eval.hs | 18 +- > src/Lambdabot/Plugin/Haskell/Pointful.hs | 201 +++++++++++++++---------------- > src/Lambdabot/Plugin/Haskell/Pretty.hs | 14 +- > src/Lambdabot/Plugin/Haskell/UnMtl.hs | 62 ++++----- > src/Lambdabot/Plugin/Haskell/Undo.hs | 115 ++++++++--------- > 5 files changed, 72 insertions(+), 75 deletions(-) > > Using the haskell-src-exts 1.18 AST, the update touches 208 lines: > src/Lambdabot/Plugin/Haskell/Pointful.hs | 87 ++++++++++++++----------------- > src/Lambdabot/Plugin/Haskell/Pretty.hs | 12 ++-- > src/Lambdabot/Plugin/Haskell/UnMtl.hs | 10 +-- > src/Lambdabot/Plugin/Haskell/Undo.hs | 34 ++++++------ > 5 files changed, 204 insertions(+), 206 deletions(-) > _______________________________________________ > Haskell-Cafe mailing list > To (un)subscribe, modify options or view archives go to: > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > Only members subscribed via the mailman list are allowed to post.

1 0

RFC: revisiting the simplified haskell-src-exts AST
by Bertram Felgenhauer 30 Jul '16

30 Jul '16

Dear all, the latest major release of haskell-src-exts (version 1.18) removed the annotation free variant of the Haskell AST. It occurred to me that using ghc's pattern synonyms it is possible to offer a light-weight simplified view on the annotated AST. For example, Language.Haskell.Exts.Syntax defines data Name l = Ident l String | Symbol l String and we can provide a simplified view with all annotations equal to () by doing {-# LANGUAGE PatternSynonyms #-} import qualified Language.Haskell.Exts.Syntax as H type Name = H.Name () pattern Ident a = H.Ident () a pattern Symbol a = H.Symbol () a Because the type isn't changed, no code has to be reimplemented to work with this AST. A first rough cut at an implementation can be found on github [1]. Before releasing it on hackage (which requires some more polishing) I'd appreciate feedback on the approach. Would you consider using such a package? Is there a better approach? Also any thoughts on usability (e.g., how to approach documentation) would be welcome. Cheers, Bertram [1] https://github.com/int-e/haskell-src-exts-simple P.S. This grew out of an effort to update lambdabot to HSE-1.18, which made me feel awful about all the superfluous and ugly () in the resulting code. I also have some numbers showing that the annotation-free view makes updating the code smoother: Using the annotation-free view, the update touches 75 lines: src/Lambdabot/Plugin/Haskell/Eval.hs | 18 +- src/Lambdabot/Plugin/Haskell/Pointful.hs | 201 +++++++++++++++---------------- src/Lambdabot/Plugin/Haskell/Pretty.hs | 14 +- src/Lambdabot/Plugin/Haskell/UnMtl.hs | 62 ++++----- src/Lambdabot/Plugin/Haskell/Undo.hs | 115 ++++++++--------- 5 files changed, 72 insertions(+), 75 deletions(-) Using the haskell-src-exts 1.18 AST, the update touches 208 lines: src/Lambdabot/Plugin/Haskell/Pointful.hs | 87 ++++++++++++++----------------- src/Lambdabot/Plugin/Haskell/Pretty.hs | 12 ++-- src/Lambdabot/Plugin/Haskell/UnMtl.hs | 10 +-- src/Lambdabot/Plugin/Haskell/Undo.hs | 34 ++++++------ 5 files changed, 204 insertions(+), 206 deletions(-)

1 0

ANN: network-2.6.3.0
by evan＠evan-borden.com 30 Jul '16

30 Jul '16

Good day, I am pleased to announce the release of network 2.6.3.0. This release is primarily focused on stability, but includes a few new APIs. Thank you to the contributors for their continued excellence. https://hackage.haskell.org/package/network-2.6.3.0 Release Notes, Version 2.6.3.0: * New maintainers: Evan Borden (@eborden) and Kazu Yamamoto (@kazu-yamamoto). The maintainer for a long period, Johan Tibell (@tibbe) stepped down. Thank you, Johan, for your hard work for a long time. * New APIs: ntohl, htonl,hostAddressToTuple{,6} and tupleToHostAddress{,6}. [#210](https://github.com/haskell/network/pull/210) * Added a Read instance for PortNumber. [#145]( https://github.com/haskell/network/pull/145) * We only set the IPV6_V6ONLY flag to 0 for stream and datagram socket types, as opposed to all of them. This makes it possible to use ICMPv6. [#180](https://github.com/haskell/network/pull/180) [#181](https://github.com/haskell/network/pull/181) * Work around GHC bug #12020. Socket errors no longer cause segfaults or hangs on Windows. [#192](https://github.com/haskell/network/pull/192) * Various documentation improvements and the deprecated pragmas. [#186](https://github.com/haskell/network/pull/186) [#201](https://github.com/haskell/network/issues/201) [#205](https://github.com/haskell/network/pull/205) [#206](https://github.com/haskell/network/pull/206) [#211](https://github.com/haskell/network/issues/211) * Various internal improvements. [#193](https://github.com/haskell/network/pull/193) [#200](https://github.com/haskell/network/pull/200)

2 2

Re: [Haskell-cafe] Breaking in library, and getting stacktrace
by Carlos D'Agostino 29 Jul '16

29 Jul '16

Without knowing too much about your project setup, and if I'm understanding correctly, see http://haddock.stackage.org/lts-5.1/base-4.8.2.0/Debug-Trace.html#v:traceSt… Keep in mind that you have to build with the corresponding flags in order to get it working correctly. Assuming you're using stack that would be: stack build --enable-profiling --library-profiling --ghc-options="-fprof-auto-rtsopts" Though I'm not sure if that's 100% what you're looking for since it doesn't break as much as that it logs with a stack trace. Hope it helps! > ---------------------------------------------------------------------- > > Message: 1 > Date: Thu, 28 Jul 2016 16:43:03 +0300 > From: Constantine Kharlamov <hi-angel(a)ya.ru> > To: haskell-cafe(a)haskell.org > Subject: [Haskell-cafe] Breaking in library, and getting stacktrace > Message-ID: <147361469713383(a)web5j.yandex.ru> > Content-Type: text/plain; charset="utf-8" > > An HTML attachment was scrubbed... > URL: < > http://mail.haskell.org/pipermail/haskell-cafe/attachments/20160728/b4652af… > > > > ------------------------------ > > Subject: Digest Footer > > _______________________________________________ > Haskell-Cafe mailing list > Haskell-Cafe(a)haskell.org > http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe > > > ------------------------------ > > End of Haskell-Cafe Digest, Vol 155, Issue 33 > ********************************************* > -- Carlos D'Agostino.

1 0

Breaking in library, and getting stacktrace
by Constantine Kharlamov 28 Jul '16

28 Jul '16

1 0

Question, re: upgrading Stack manually.
by David Banas 27 Jul '16

27 Jul '16

Hi Stackers, Is this a show stopper, wrt/ upgrading Stack manually, via: - stack unpack stack-1.1.2 - pushed <directory created, above> - stack setup - stack build Warning: /Users/dbanas/Documents/Projects/stack/upgrade_2016-07-27/stack-1.1.2/stack.yaml: Unrecognized field in ProjectAndConfigMonoid: nix ? Thanks, -db

2 1

good choice for random number generator ?
by briand＠aracnet.com 27 Jul '16

27 Jul '16

There's quite a few. Many are very old. I would have like to use vector-random and got this : Data/Vector/Random/Mersenne.hs:33:18: Could not find module ‘Data.Vector.Fusion.Stream’ It is a member of the hidden package ‘vector-0.10.12.3@vecto_1COyUuV1LrA1IjYnWfJnbs’. Perhaps you need to add ‘vector’ to the build-depends in your .cabal file. Use -v to see a list of the files searched for. Data/Vector/Random/Mersenne.hs:35:18: Could not find module ‘Data.Vector.Fusion.Stream.Size’ It is a member of the hidden package ‘vector-0.10.12.3@vecto_1COyUuV1LrA1IjYnWfJnbs’. Perhaps you need to add ‘vector’ to the build-depends in your .cabal file. Use -v to see a list of the files searched for. I wouldn't be opposed to fixing it, but I'm wondering at this point there isn't a better package to use instead. I'm looking for both integer and floating point random numbers, uniform and gaussian. gsl-random looks promising as does mwc-random. any other suggestions ? Thanks, Brian

6 10

How do I debug this RTS segfault?
by Lana Black 26 Jul '16

26 Jul '16

Hello, I have run into this RTS bug recently. In short, when executing multiple consequtive forks, after 500-600 or so the process is terminated by SIGSEGV. I know this kind of thing is totally artificial, but still. The problem I have is that I can't get any meaningful backtrace in gdb. For example, for threaded RTS I get this (gdb) bt #0 0x0000000000560d63 in base_GHCziEventziThread_ensureIOManagerIsRunning1_info () Backtrace stopped: Cannot access memory at address 0x7fffff7fcea0 For non-threaded RTS I get this (gdb) bt #0 0x00000000007138c9 in stg_makeStablePtrzh () Backtrace stopped: Cannot access memory at address 0x7fffff7fc720 Build command: ghc --make -O2 -g -fforce-recomp fork.hs Add threaded if needed. I was able to reproduce this bug with both GHC 7.10.3 and todays HEAD with the code below. >import System.Exit (exitSuccess) >import System.Posix.Process (forkProcess) > >fork_ n | n > 0 = processPid =<< forkProcess (fork_ $! n - 1) > | otherwise = putStrLn "I'm done!" > >processPid pid | pid > 0 = exitSuccess > | pid < 0 = putStrLn "OOOPS, forkProcess failed!" > | otherwise = pure () > >main = fork_ 1000 > With best regards.

4 5

Forcing the kind in data
by Michael Roth 26 Jul '16

26 Jul '16

Hi, if I have: data Foobar a b = Foobar it has kind: * -> * -> * How can I force the kind to: (* -> *) -> * -> * ? Thank you!

3 2

Different behaviour with -XAllowAmbiguousTypes in 7.10.3b and 8.0.1
by Max Amanshauser 26 Jul '16

26 Jul '16

Hi, while porting a library to Haskell, which deals with persisting finite state automata to various stores, depending on the user's choice and the instances provided for types s(tate) e(vent) a(ction), I ran into different behaviour in ghc 7.10.3b and 8.0.1 related to ambiguity checks. This is a minimised and somewhat contrived example: > -- testme.hs > > {-# LANGUAGE MultiParamTypeClasses #-} > {-# LANGUAGE FlexibleInstances #-} > {-# LANGUAGE AllowAmbiguousTypes #-} > > module TestMe where > > data MyStore = MyStore > > class FSMStore st s e a where > fsmRead :: st -> String -> s > > instance (Num s) => FSMStore MyStore s e a where > fsmRead st i = 23 > > get :: (FSMStore st s e a) => st -> String -> s > get st i = fsmRead st i With GHC 8.0.1 I get: > *TestMe> :l test.hs > [1 of 1] Compiling TestMe ( test.hs, interpreted ) > > test.hs:19:12: error: > • Could not deduce (FSMStore st s e0 a0) > arising from a use of ‘fsmRead’ > from the context: FSMStore st s e a > bound by the type signature for: > get :: FSMStore st s e a => st -> String -> s > at test.hs:18:1-47 > The type variables ‘e0’, ‘a0’ are ambiguous > Relevant bindings include > st :: st (bound at test.hs:19:5) > get :: st -> String -> s (bound at test.hs:19:1) > These potential instance exist: > instance Num s => FSMStore MyStore s e a > -- Defined at test.hs:12:10 > • In the expression: fsmRead st i > In an equation for ‘get’: get st i = fsmRead st i > Failed, modules loaded: none. However, when I remove the type signature for get: > Prelude> :l test.hs > [1 of 1] Compiling TestMe ( test.hs, interpreted ) > Ok, modules loaded: TestMe. > *TestMe> :t get > get :: FSMStore st s e a => st -> String -> s > *TestMe> get MyStore "asdf" > 23 GHC inferred the exact same type I provided, but this time it compiles successfully. When going back to GHC 7.10.3b, without type signature: > GHCi, version 7.10.3: http://www.haskell.org/ghc/ :? for help > :Prelude> :l test.hs > [1 of 1] Compiling TestMe ( test.hs, interpreted ) > > test.hs:19:1: > Could not deduce (FSMStore st s e0 a0) > from the context (FSMStore st s e a) > bound by the inferred type for ‘get’: > FSMStore st s e a => st -> String -> s > at test.hs:19:1-23 > The type variables ‘e0’, ‘a0’ are ambiguous > When checking that ‘get’ has the inferred type > get :: forall st s e a. FSMStore st s e a => st -> String -> s > Probable cause: the inferred type is ambiguous > Failed, modules loaded: none. So my questions are: *) What's with the different behaviour depending on whether the type sig is inferred or provided? *) Is GHC 7.10.3b or 8.0.1 closer to the correct behaviour w.r.t. -XAllowAmbiguousTypes? -- Regards, Max Amanshauser.

2 1

Use GHC API in standalone executable?
by Phyx 25 Jul '16

25 Jul '16

I guess this depends on what you want to do. I've seen various level of GHC API usage in standalone applications, but it just depends on how much of the compiler pipeline you want to use. Their are ways to override the paths or provide stubs for programs ghc expects to be there. I've packaged API calls into shared libraries myself before, in that case I was mostly accessing the compiler frontend.

1 0

Is there any way in GHC plugin to refer exposed but defined in a hidden module?
by Hiromi ISHII 25 Jul '16

25 Jul '16

Hi Cafe, I'm currently writing a simple GHC Typechecker plugin to augment typelevel naturals with a presburger arithmetic solver [^1]. I want to use type-class constraints to give premisses to the solver, for example, `Empty a` constraint means "a is false (empty type)". So I have to get TyCon information in TcPluginM monad and I wrote as follows: ```haskell do md <- lookupModule (mkModuleName "Proof.Propositional.Empty") (fsLit "equational-reasoning") classTyCon <$> (tcLookupClass =<< lookupOrig md (mkTcOcc "Empty")) ``` But this code doesn't work as expected. For example, the code ```haskell {-# LANGUAGE DataKinds, TypeOperators, GADTs, TypeFamilies, ExplicitForAll, FlexibleContexts #-} import Data.Type.Equality import GHC.TypeLits (type (+), type (<=), type (<=?)) import Proof.Propositional (Empty(..)) predSucc :: Empty (n :~: 0) => proxy n -> (n + 1 <=? n + n) :~: 'True predSucc _ = Witness ``` resulted in the following compile-time error: ``` Can't find interface-file declaration for type constructor or class equational-reasoning-0.4.0.0:Proof.Propositional.Empty Probable cause: bug in .hi-boot file, or inconsistent .hi file Use -ddump-if-trace to get an idea of which file caused the error ``` The probem is, Empty class is provided by separate existing package [^2], but is once defined in hidden module and re-exported from exposed from exposed module. If I expose the module where Empty is originally defined and change the module name passed to lookupModule appropriately, then the first code becomes working as expected. So the question: is there any way to retrieve TyCon information defined in hidden module but exported? [^1]: https://github.com/konn/ghc-typelits-presburger/ [^2]: https://github.com/konn/equational-reasoning-in-haskell -- Hiromi ISHII konn.jinro(a)gmail.com Doctoral program in Mathematics, University of Tsukuba

1 0

linking dlls with relative paths on Windows
by Phyx 25 Jul '16

25 Jul '16

Hi Peter, I forgot to respond to this, if you haven't received an answer to this yet then feel free to open a ticket on the ghc trac and I will take a look as soon as I have working Internet again. I don't know what the status is of this for now, the linked to stackoverfow article should work though. Also 7.10.3 has some issues when loading dependent dlls in the same folder as the main one being loaded when not on the search path. 8.0.1 should be fine. Kind regards, Tamar

1 0

Munich Haskell Meeting, 2016-07-27 @ 19:30 Augustiner Bierhalle
by Christian Neukirchen 25 Jul '16

25 Jul '16

Dear all, This week, our monthly Munich Haskell Meeting will take place again on Wednesday, July 27 at Augustiner Bierhalle (Neuhauser Str.) at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle so we can reserve enough seats! It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-jul-2016/ Everybody is welcome! cu, -- Christian Neukirchen <chneukirchen(a)gmail.com> http://chneukirchen.org

1 0