- Haskell-Cafe - Haskell.org

Annotations in abstract syntax tree
by j.romildo＠gmail.com 27 Apr '12

27 Apr '12

Hello. I need to annotate abstract syntax tree with additional information in a compiler. Using the Annotations package[1] I have written the following small program: import Annotations.F.Annotated import Annotations.F.Fixpoints data ExprF r = Num Double | Var String | Add r r | Sub r r | Mul r r | Div r r deriving (Eq,Show) type BareExpr = Fix ExprF e :: BareExpr e = In (Mul (In (Num 5)) (In (Add (In (Var "x")) (In (Num 8))))) type ValExpr = Fix (Ann Double ExprF) type Memory = [(String,Double)] eval :: Memory -> BareExpr -> ValExpr eval _ (In (Num x)) = In (Ann x (Num x)) eval m (In (Var x)) = let y = case lookup x m of Just k -> k Nothing -> 0 in In (Ann y (Var x)) eval m (In (Add x y)) = op m (+) Add x y eval m (In (Sub x y)) = op m (-) Sub x y eval m (In (Mul x y)) = op m (*) Mul x y eval m (In (Div x y)) = op m (/) Div x y op m f k x y = let x'@(In (Ann v1 _)) = eval m x y'@(In (Ann v2 _)) = eval m y in In (Ann (f v1 v2) (k x' y')) With these definitions we can represent simple arithmetic expressions and we can also evaluate them, annotating each node in the abstract syntax tree with its corresponding value. Now I want to add statements to this toy language. One statement may be a print statement containing an expression whose value is to be printed, an assign statement containing an identifier and an expression, or a compound statement containing two statements to be executed in sequence. How the data types for statements can be defined? How a function to execute an statement anotating its node with the corresponding state (memory plus output) after its execution can be defined? Without annotations the type of statements could be: data Stm = PrintStm Expr | AssignStm String Expr | CompoundStm Stm Stm How to enable annotations in this case? Note that Stm uses both Expr and Stm. [1] http://hackage.haskell.org/package/Annotations Romildo

4 6

Automatic discovery of tests
by G 27 Apr '12

27 Apr '12

Hi, trying to learn haskell and the associated build env. I come from a java/scala world so trying to understand the how to invoke tests. Have a cabal file that invokes a main function to execute a test. But wondering if there is any automatic discovery of tests as per junit. I have seen test-framework-th but to me that implies putting a testGroupGenerator into each module. Am i correct about that and if so is there an example of calling multiple modules tests ? Or is there a better way just to invoke specific functions prefixed with case_ prop_ etc in the entire src/test directory of the cabal build ? Thanks

1 0

Re: [Haskell-cafe] [Haskell] ANN: Portackage - a hackage portal
by Andrew Seniuk 27 Apr '12

27 Apr '12

Excuse the delay, I have no home internet. > On Fri, Apr 27, 2012 at 1:16 AM, <briand(a)aracnet.com> wrote: > Great idea. Maybe the format can start as compactly as possible, > i.e. 1 entry per line to make it easy to browse as many entries > as possible in one page. > > It looks as though disabling just the dependencies would go a > long way to accomplish that. Yep, and in fact the version I uploaded while reading your message has the deps column elided (and one or two others). Enforcing single-line rows is a but a few tweaks away. The thing is, the module namespace was the main motivator for this project, so I'm also seeing whether I can get away with a single view, package-oriented as presently, and still give good focus to the modules names. Soon I hope to include "accordion" views of the module namespace, with cookie-based (?) persistent state so user's collapse/expand tree state is preserved. > I'd like to vote to make the synopsis to be the second column. > > will each column type have an enable/disable ? I like the idea (although that one wasn't in the upload). Hopefully when I explore the JavaScript UI tools a bit more, the columns (key structure) will be totally configurable by drag-and-drop, with columns sizable, and keys selected from a listbox. (?) stuff like that > it's probably best if a click on a specific target, say the actual > name of the package, sends you to the hackage entry instead of a > click anywhere on the row. I find myself clicking on the page > by accident and it sending me off to some random hackage entry. :) That's a feature! But seriously, you're right, and as a bonus the links can be specific to the columns (package -> hackage, modules -> API pages, homepages -> hps, maintainer -> sendto [1]). (A 2-finger or Mod- click anywhere on a row might still be nice, but a bare tap is admittedly way too accident prone with touch input.) > I really like the idea - makes your hackage surfing > much more enjoyable ! > > Brian And thank-you for sharing your thoughts! I'm committed to improving it, until the ideas run out. > On Fri, Apr 27, 2012 at 4:12 AM, Christoph Breitkopf <chbreitkopf(a)googlemail.com> wrote: > this already looks great. So here's my wish-list, in case you have > too much time on yours hands ;-) Thanks! Yes I suppose I do have too much time on my hands, but the pain of that is conterbalanced by all the excitement. > Quality/popularity indicators (I'm aware that some of these are > real work and better provided by hackage itself): > - used by how many other packages (number of edges to that package > in the dependency graph of all packages) > - haddock coverage, test coverage, etc. > - like, +1, whatnot button > - link to issue tracker, if there is one If there's interest, this could become integrated with hackage at some point in the future. Next thing is to get a "last upload" field which can replace the version field. The codependency graph :) would be a nice metric to add, I'll look into it. I remember seeing a package that does this someplace on hackage. The +1 button is a good one! In short I'll try to implement all these ideas, thanks to you both for the encouraging comments. -Andrew [1] I omitted the maintainer column, thinking its inclusion might be harmful, making the emails so easy for a bot to collect.

1 0

ANN: Portackage - a hackage portal
by Andrew Seniuk 27 Apr '12

27 Apr '12

Hello, This is to announce a provisional webpage to summarise hackage.haskell.org. http://www.fremissant.net/portackage It is a lot of data, so will be a bit slow to load. Columns can be sorted by clicking the headers, but this will also take some seconds on a typical client. The initial sort is by module name. Clicking a table row links to the project page on hackage. Although I believe this is a complete list of all packages/modules in hackage, it is probably still buggy, so if you see anything amiss please let me know. Also, a subsequent version in the near future will update automatically based on the http://hackage.haskell.org/packages/archive/recent.rss RSS feed, but for now it's based on a recent snapshot. Haskell code which prepares the page will be released after a few more days testing and refinement. Some previous work [1] provided a list of all modules, but is not being maintained, and I was unable to rearouse the author's interest. Feature requests and suggestions are welcome! Kind Reg'ds, Andrew Seniuk [1] http://folk.ntnu.no/hammar/explore-hackage/

1 1

Re: [Haskell-cafe] [Haskell] ANN: Portackage - a hackage portal
by Andrew Seniuk 26 Apr '12

26 Apr '12

Jonathan, On Thu, Apr 26, 2012 at 4:13 PM, Jonathan Daugherty <jtd(a)galois.com> wrote: >> Although I believe this is a complete list of all packages/modules in >> hackage, it is probably still buggy, so if you see anything amiss >> please let me know. > > It might not be showing the most recent releases of everything. As an > example, it shows a much older version of my vty-ui library (1.0) and > its metadata, instead of the latest version, 1.5. As a result the > version, module list, description, homepage, etc., are not current. Thank-you, I'd realised this issue but forgot to address it. It is due to a false assumption on my part that the .cabal entries in the 00-index.tar file were in increasing version order. I'll address this problem today. Cheers, Andrew

1 1

ANN: signed-multiset-0.1
by Stefan Holdermans 26 Apr '12

26 Apr '12

I am pleased to announce the first release of signed-multiset, which implements an abstract datatype for multisets with negative membership. The package can be obtained from http://hackage.haskell.org/package/signed-multiset-0.1 As always, feedback is welcome. Cheers, Stefan signed-multiset-0.1 ------------------- Multisets (or bags) are sets in which elements may occur more than once. The number of times an element occurs in a multiset is called its multiplicity. This package provides an efficient implementation of so-called signed multisets, which generalise multisets by allowing for negative membership. That is, elements in a signed multiset can have negative multiplicities. See also: Wayne D. Blizard. Negative membership. Notre Dame Journal of Formal Logic/, 31(3):346--368, 1990.

7 29

JSON library suggestions?
by Jeff Shaw 26 Apr '12

26 Apr '12

Hello, Up until now I've been using Aeson, but I've found that its number type isn't going to work for me. I need to use decimal numbers while avoiding conversions from and to Double, which Aeson doesn't allow. There are quite a few more JSON libraries for Haskell, which all appear to use Rational for numbers, so I'm wondering if anyone can recommend one. Thanks, Jeff

5 7

Haskell Weekly News: Issue 224
by Daniel Santa Cruz 26 Apr '12

26 Apr '12

Welcome to issue 224 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of April 15 to 21, 2012. Announcements Some of these announcements are a bit behind, for which I apologize. Better late than never... The long awaited version of cabal-install is out! [1] http://goo.gl/LlO7s Janis Voigtlander is looking for contributors for the May 2012 edition of the Haskell Comunities and Activities Report. If you have anything Haskell related that you have been working on, make sure to send Janis a note. The deadline is May 1st. [2] http://goo.gl/AW3gR Jeremy O'Donoghue announced the release of wxHaskell 0.90. "his release represents a significant milestone for us as it includes support for wxWidgets 2.9.x." [3] http://goo.gl/vTYTp Janis Voigtlander also issued a call for papers for the Haskell Symposium 2012, Copenhagen, Denmark on 13th September, 2012, directly after ICFP. [4] http://goo.gl/fR2hB Eric Kow released the 9th edition of the Parallel Haskell Digest. [5] http://goo.gl/gBIhK Quotes of the Week * TSC: The type families might have little type children * mm_freak: i'd love to have an embeddable Agda type checker and evaluator mm_freak: that would make a great scripting language for haskell programs * shachaf: You can't spell "-funsafe" without "fun" and "safe". * elliott: By the way, I find the inclusion of a package named "colour" in a section titled "Color" offensive :) * elliott: I don't think Haskell can ever hope to enter the enterprise if we can't model non-standard colourblind observers with it. * danharaj:oh hey this looks nice. Mathnerd314: every open-source math library under the sun glued together into a Python framework danharaj: nevermind o_o * elliott: What do we do with people who paste code blocks on IRC? We yell at them. * acowley: I am a bull in a math shop * elliott: I like how edwardk's answer to every question always goes "most abstract solution to the problem possible --> microoptimisation details". elliott: I swear I've seen him go from category theory to unboxed types and unsafeCoerce in a single line of IRC. * shachaf: It is a sobering thought that by the time Galois was my age, he had been dead for almost two months. Top Reddit Stories * Why do Monads Matter? (or it's Monad tutorial season again) Domain: cdsmith.wordpress.com, Score: 64, Comments: 27 On Reddit: [6] http://goo.gl/DCJYV Original: [7] http://goo.gl/8glhF * Ur/Web records: can we apply lessons from them to Haskell? Domain: blog.ezyang.com, Score: 53, Comments: On Reddit: [8] http://goo.gl/9m3Sw Original: [9] http://goo.gl/dNcET * Blank Canvas - a new Haskell graphics library based on HTML5 and <canvas> Domain: ittc.ku.edu, Score: 42, Comments: 10 On Reddit: [10] http://goo.gl/H3SMB Original: [11] http://goo.gl/if7kG * Client Side Yesod, an FRP-inspired approach Domain: yesodweb.com, Score: 41, Comments: 44 On Reddit: [12] http://goo.gl/gECTq Original: [13] http://goo.gl/Rn0LS * Understanding Haskell Kinds Domain: softwaresimply.blogspot.com, Score: 38, Comments: 18 On Reddit: [14] http://goo.gl/XxiwQ Original: [15] http://goo.gl/xaqDM * Adding SIMD Support to Data Parallel Haskell Domain: ghc-simd.blogspot.co.uk, Score: 35, Comments: 8 On Reddit: [16] http://goo.gl/R8M9L Original: [17] http://goo.gl/ZeJ7e * Working With HTML In Haskell Domain: adit.io, Score: 31, Comments: 24 On Reddit: [18] http://goo.gl/4NMBc Original: [19] http://goo.gl/EOvM1 * Descending the level ladder Domain: monoidal.blogspot.com, Score: 26, Comments: 13 On Reddit: [20] http://goo.gl/9IYZL Original: [21] http://goo.gl/TJm0D * Why is Haskell so large? Domain: self.haskell, Score: 25, Comments: 29 On Reddit: [22] http://goo.gl/KQnbj Original: [23] http://goo.gl/KQnbj * Parallel Haskell Digest 9: GSoC, STM, SIMD, and the Downfall of Imperative Programming? Domain: well-typed.com, Score: 25, Comments: 1 On Reddit: [24] http://goo.gl/Z5bF3 Original: [25] http://goo.gl/eLnVs * blaze-html 0.5 released Domain: jaspervdj.be, Score: 25, Comments: 3 On Reddit: [26] http://goo.gl/7XtMD Original: [27] http://goo.gl/RkbR7 * Four Tips for New Haskell Programmers Domain: softwaresimply.blogspot.com, Score: 22, Comments: 72 On Reddit: [28] http://goo.gl/GQ4O1 Original: [29] http://goo.gl/Ye57L * Check for interest - an argument/option parser using type level strings Domain: self.haskell, Score: 22, Comments: 13 On Reddit: [30] http://goo.gl/eOtE5 Original: [31] http://goo.gl/eOtE5 * New Cabal feature: cabal bench Domain: blog.johantibell.com, Score: 22, Comments: 3 On Reddit: [32] http://goo.gl/ClkjJ Original: [33] http://goo.gl/sA3aD Top StackOverflow Questions * The Pause monad votes: 20, answers: 5 Read on SO: [34] http://goo.gl/DNIo1 * To what extent are macros “functions in reverse?” votes: 15, answers: 6 Read on SO: [35] http://goo.gl/ZoEht * Curry-Howard isomorphism votes: 13, answers: 3 Read on SO: [36] http://goo.gl/1pzKd * How does Djinn work? votes: 12, answers: 3 Read on SO: [37] http://goo.gl/RnEny * How is co-recursion handled? votes: 12, answers: 2 Read on SO: [38] http://goo.gl/DXtj1 * Distinction between typeclasses MonadPlus, Alternative, and Monoid? votes: 11, answers: 1 Read on SO: [39] http://goo.gl/4LZd7 * Why can't Existential Types use record syntax? votes: 11, answers: 2 Read on SO: [40] http://goo.gl/4Gn96 * Given a Haskell type signature, is it possible to generate the code automatically? votes: 11, answers: 4 Read on SO: [41] http://goo.gl/7Xff3 * Is it possible to force a type to a class in Haskell? votes: 10, answers: 6 Read on SO: [42] http://goo.gl/SeFpb * Haskell concurrency - is forkIO really nondeterministic? votes: 10, answers: 2 Read on SO: [43] http://goo.gl/z2q9Y * Where to find programming exercises for applicative functors? votes: 9, answers: 4 Read on SO: [44] http://goo.gl/CXOYU Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.general/19239 2. http://www.haskell.org/pipermail/haskell/2012-April/023244.html 3. http://permalink.gmane.org/gmane.comp.lang.haskell.wxhaskell.general/1178 4. http://permalink.gmane.org/gmane.comp.science.types.announce/2949 5. http://permalink.gmane.org/gmane.comp.lang.haskell.cafe/97851 6. http://cdsmith.wordpress.com/2012/04/18/why-do-monads-matter/ 7. http://www.reddit.com/r/haskell/comments/sfvbu/why_do_monads_matter_or_its_… 8. http://blog.ezyang.com/2012/04/how-urweb-records-work-and-what-it-might-mea… 9. http://www.reddit.com/r/haskell/comments/sjoh5/urweb_records_can_we_apply_l… 10. http://ittc.ku.edu/csdl/fpg/Tools/BlankCanvas 11. http://www.reddit.com/r/haskell/comments/seppr/blank_canvas_a_new_haskell_g… 12. http://www.yesodweb.com/blog/2012/04/client-side 13. http://www.reddit.com/r/haskell/comments/sm72n/client_side_yesod_an_frpinsp… 14. http://softwaresimply.blogspot.com/2012/04/less-travelled-monad-tutorial-pa… 15. http://www.reddit.com/r/haskell/comments/scagx/understanding_haskell_kinds/ 16. http://ghc-simd.blogspot.co.uk/2012/04/adding-simd-support-to-data-parallel… 17. http://www.reddit.com/r/haskell/comments/sfxck/adding_simd_support_to_data_… 18. http://adit.io/posts/2012-04-14-working_with_HTML_in_haskell.html 19. http://www.reddit.com/r/haskell/comments/sbxhb/working_with_html_in_haskell/ 20. http://monoidal.blogspot.com/2012/04/descending-level-ladder.html 21. http://www.reddit.com/r/haskell/comments/scq1q/descending_the_level_ladder/ 22. http://www.reddit.com/r/haskell/comments/sb80y/why_is_haskell_so_large/ 23. http://www.reddit.com/r/haskell/comments/sb80y/why_is_haskell_so_large/ 24. http://www.well-typed.com/blog/65 25. http://www.reddit.com/r/haskell/comments/sjbgv/parallel_haskell_digest_9_gs… 26. http://jaspervdj.be/posts/2012-04-21-blaze-html-0.5.html 27. http://www.reddit.com/r/haskell/comments/sl6ps/blazehtml_05_released/ 28. http://softwaresimply.blogspot.com/2012/04/four-tips-for-new-haskell-progra… 29. http://www.reddit.com/r/haskell/comments/sarkz/four_tips_for_new_haskell_pr… 30. http://www.reddit.com/r/haskell/comments/sbpmz/check_for_interest_an_argume… 31. http://www.reddit.com/r/haskell/comments/sbpmz/check_for_interest_an_argume… 32. http://blog.johantibell.com/2012/04/cabal-bench.html 33. http://www.reddit.com/r/haskell/comments/sfhv3/new_cabal_feature_cabal_benc… 34. http://stackoverflow.com/questions/10236953/the-pause-monad 35. http://stackoverflow.com/questions/10249110/to-what-extent-are-macros-funct… 36. http://stackoverflow.com/questions/10212660/curry-howard-isomorphism 37. http://stackoverflow.com/questions/10217931/how-does-djinn-work 38. http://stackoverflow.com/questions/10257326/how-is-co-recursion-handled 39. http://stackoverflow.com/questions/10167879/distinction-between-typeclasses… 40. http://stackoverflow.com/questions/10192663/why-cant-existential-types-use-… 41. http://stackoverflow.com/questions/10205793/given-a-haskell-type-signature-… 42. http://stackoverflow.com/questions/10211664/is-it-possible-to-force-a-type-… 43. http://stackoverflow.com/questions/10247555/haskell-concurrency-is-forkio-r… 44. http://stackoverflow.com/questions/10239630/where-to-find-programming-exerc…

1 0

"desactivate" my Show instance implementations temporarily
by TP 25 Apr '12

25 Apr '12

Hello, I have a module where I have made several types as instances of the Show typeclass. For debugging purpose, I would like to use the default implementation for Show (the one obtained when using "deriving", which shows all the constructors). Is there some option to do that, or have I to comment all the Show instances of my code, and add "Show" in "deriving (...)" for each of my types? If this is the only possibility, is there some script around here to do that automatically? Thanks in advance, TP

5 6

Multi-site haddock documentation with proper links?
by Ryan Newton 25 Apr '12

25 Apr '12

Hello cafe, For various reasons, some packages don't build documentation on hackage: http://hackage.haskell.org/package/accelerate Therefore I want to locally install documentation for a set of packages like this and host them on a separate website. I want all of these ~ten packages' haddock documentation to be properly interlinked with eachother, but also to link to Hackage for types and classes defined in other modules. Is this possible? Hackage haddocks are all interlinked, but that is simply because hackage is one giant local install, right? If it's not possible (and it seems not) do any haddock devs have pointers on how to implement this? Thanks, -Ryan P.S. Someone recommended to me the following simple hack -- just use sed to rewrite the links after haddock generates the html. I think I'll do that for the time being unless someone has a better suggestion.

2 3