- Haskell-Cafe - Haskell.org

what is basic Haskell?
by Johan Larson 25 Jul '14

25 Jul '14

What does a programmer need to know to be proficient in "basic Haskell"? For my money, basic programming skills are those that are required to write programs for simple tasks in the common idioms of the language. This means the practitioner should be able to read input from the terminal or files, select/combine/reformat data, and output a result. At this point, efficiency isn't really the point; only getting to a correct answer without writing anything really weird matters. In LYAH, I'd put the boundary at the end of chapter 9, which covers the IO monad. At that point the reader has studied functions, lists, tuples, types, recursion, higher order functions, four major modules, and algebraic data types. Actually, some of the later topics in chapter 8 (functors, kinds, recursive data structures) seem more like intermediate material. Thoughts? -- Johan Larson -- Toronto, Canada

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Markov Text Generator & Randomness
by Charles-Pierre Astolfi 24 Jul '14

24 Jul '14

Hi -cafe, I'm coding a Markov Text Generator (of order 1). Basically, you have a source text, and knowing the frequencies of pairs of consecutive words, you generate a somewhat syntactically correct text from this. Here's the link to my code and to a source text you can use as example. test.txt http://lpaste.net/raw/4004174907431714816 code http://lpaste.net/4147715261379641344 The kickers is that this code generates sentences with consecutive words that never appears next to each other in the source text. For example, the code generated "They sat over at because old those the lighted.", but "over at" never occurs in the source text, so it shouldn't occur in a generated sentence. The makeDb function gives is correct, so my problem actually lies in generate and/or in draw. I think there's something about RVar that I messed up, but I don't see the problem. Any ideas? Cheers, -- Charles-Pierre

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Haskell on JVM (using LLVM backend)
by Wojciech Danilo 24 Jul '14

24 Jul '14

Hello! I was recently discussing with some frients possibilities of running Haskell programs on JVM. I belive such possibility could be a breakdown for the popularity of Haskell and could be very interesting for new people and new usage-scenarios. I have seen some topics, like these: http://stackoverflow.com/questions/7261039/haskell-on-jvm http://www.haskell.org/haskellwiki/GHC/FAQ#Why_isn.27t_GHC_available_for_.N… http://www.haskell.org/pipermail/haskell-cafe/2009-June/063454.html but are a little old and do NOT mention the LLVM backend. If we've got the LLVM backend in GHC right now, why cannot we just use something like LLJVM to convert the LLVMIR into JVM bytecode? I understand that the LLVM bytecode (optained from GHC) has all the optimizations applied (including tail recursion expansion) so it **could** be possible to just run it on JVM? All the best, Wojciech Daniło

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Re: [Haskell-cafe] determining the origin of imported symbols
by Erik Rantapaa 24 Jul '14

24 Jul '14

Thanks, everyone, for all of the suggestions! On Thursday, July 24, 2014 5:53:59 AM UTC-5, Eyal Lotem wrote: > > There's also ghc's -ddump-minimal-imports which might help you. > > > On Thu, Jul 24, 2014 at 12:06 PM, JP Moresmau <jpmor...@gmail.com > <javascript:>> wrote: > >> BuildWrapper doesn't do the transformation, but it resolves all symbols >> to build a usage map, so it would tell you that Data.List.sort is used at >> line xxx, using the GHC API. So have a look at around >> https://github.com/JPMoresmau/BuildWrapper/blob/master/src/Language/Haskell…. >> BuildWrapper takes the GHC AST, transforms it into a JSON structure, and >> extracts all usage information. There is also an import reorganization >> function that may be useful. >> >> JP >> >> >> On Thu, Jul 24, 2014 at 10:29 AM, Erik Rantapaa <eran...@gmail.com >> <javascript:>> wrote: >> >>> Hi everyone, >>> >>> I looking for a way to analyze Haskell source to determine which module >>> each imported symbol comes from. My goal is to transform source code like >>> this: >>> >>> import Data.List >>> ... >>> main = do >>> nums <- fmap (map read . words) getLine :: IO [Int] >>> print $ sort nums >>> >>> to code like this: >>> >>> import qualified Prelude as B >>> import qualified Data.List as A >>> ... >>> main = do >>> nums <- B.fmap (B.map B.read B.. B.words) B.getLine :: B.IO >>> [B.Int] >>> B.print B.$ A.sort nums >>> >>> That is, I want to qualify all imported symbols with a module alias. >>> >>> Can anyone suggest modules or programs I should look at? >>> >>> Thanks, >>> ER >>> >>> _______________________________________________ >>> Haskell-Cafe mailing list >>> Haskel...@haskell.org <javascript:> >>> http://www.haskell.org/mailman/listinfo/haskell-cafe >>> >>> >> >> >> -- >> JP Moresmau >> http://jpmoresmau.blogspot.com/ >> >> -- >> You received this message because you are subscribed to the Google Groups >> "Haskell-cafe" group. >> To unsubscribe from this group and stop receiving emails from it, send an >> email to haskell-cafe...@googlegroups.com <javascript:>. >> To post to this group, send email to haskel...@googlegroups.com >> <javascript:>. >> Visit this group at http://groups.google.com/group/haskell-cafe. >> For more options, visit https://groups.google.com/d/optout. >> > > > > -- > Eyal >

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determining the origin of imported symbols
by Erik Rantapaa 24 Jul '14

24 Jul '14

Hi everyone, I looking for a way to analyze Haskell source to determine which module each imported symbol comes from. My goal is to transform source code like this: import Data.List ... main = do nums <- fmap (map read . words) getLine :: IO [Int] print $ sort nums to code like this: import qualified Prelude as B import qualified Data.List as A ... main = do nums <- B.fmap (B.map B.read B.. B.words) B.getLine :: B.IO [B.Int] B.print B.$ A.sort nums That is, I want to qualify all imported symbols with a module alias. Can anyone suggest modules or programs I should look at? Thanks, ER

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OverlappingInstances-extension-like for type families
by Leza Morais Lutonda 23 Jul '14

23 Jul '14

Hello haskell-café, I just started working with type families, and come with some difficulties. Now I have a class: class (...) ⇒ Complexable s where type ComplexSignalType s ... Is there a possibility to have this two instances (in any way)? instance (RealFloat e) ⇒ Complexable [e] where type ComplexSignalType [e] = [ℂ e] instance (RealFloat e) ⇒ Complexable [ℂ e] where type ComplexSignalType [ℂ e] = [ℂ e] Thanks. -- Leza Morais Lutonda, Lemol-C http://lemol.github.io 50 Aniversario de la Cujae. Inaugurada por Fidel el 2 de diciembre de 1964 http://cujae.edu.cu

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How many Haskell programmers are there?
by Johan Larson 23 Jul '14

23 Jul '14

Obviously this is a very fuzzy question. But what's the credible range of answers? Here's one: http://steve-yegge.blogspot.ca/2010/12/haskell-researchers-announce-discove… 38 -- Johan Larson -- Toronto, Canada

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Looking for list comprehensions use cases
by Jan Stolarek 23 Jul '14

23 Jul '14

Haskellers, recently I've been looking into the possibility of creating some new optimisations for GHC. These would be mostly aimed at list comprehensions. Here's where I need your help: 1. Do you have complex list comprehensions usage examples from real code? By complex I mean nested list comprehensions, reading from more than one list ([ ...| x <- xs, y <- ys ... ]) etc. 2. Do you have list comprehensions code that you had to optimize by hand because GHC was unable to make them fast enough? Janek

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Call for participation: Haskell tutorial at CUFP on 4 Sep 2014
by Stefan Wehr 22 Jul '14

22 Jul '14

Dear Haskellers, I'll be giving an advanced Haskell tutorial as part of the CUFP 2014 workshop. * Date/time: 4 Sep 2014, 9:00 AM - 12:30 PM * Place: Gothenburg, Sweden (affiliated with ICFP 2014) * Early registration deadline: 3 Aug 2014! The tutorial teaches important techniques for writing correct, robust, scalable, and fast Haskell programs. The topics covered are: network programming, serialization, persistence, logging, performance, scalability, testing, and concurrency. The tutorial aims at programmers with some Haskell experience. It is not necessary to be an Haskell expert, but you should know how to write functions and data types. For more details, see http://cufp.org/2014/t2-stefan-wehr-haskell-in-the-real-world.html Registration page: https://regmaster4.com/2014conf/ICFP14/register.php Please distribute this call for participation. See you in Gothenburg! Stefan

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Elementary algorithms - (Haskell language is used)
by Xinyu LIU 22 Jul '14

22 Jul '14

Hi, I spent 6 years to write the book ‘Elementary Algorithms’. I finally completed it yesterday. This book is open and free, the PDF version can be downloaded from: https://github.com/liuxinyu95/AlgoXY/blob/algoxy/preview/elementary-algorit… Why There are plenty of books about algorithms, such as ‘Introduction to algorithms’, ‘The art of computer programming’, ‘structure and interpretation of computer programs’… why another book? Is it reinvention of wheel? This book can’t compare with the above classic bibles at all. It has some features like: 1. All algorithms are described in math formulas and pseudo codes. I hope it bring some taste of elegant by using algebraic symbols. 2. All algorithms are realized in both purely functional and imperative approaches. 3. The examples are provided in multiple programming languages, including C, Haskell, Python, C++, Scheme/Lisp. Haskell is the main language for all functional implementations. Content The following content are covered in this book (in the order of appearance) • Binary search tree, insertion sort, red-black tree, AVL tree, Trie, Patricia, suffix tree, B-tree; • Binary heap, Leftist heap, skew heap, splay heap, selection sort, binomial heap, Fibonacci heap, pairing heap; • Queue, Finger tree based sequence, quick sort, merge sort, binary search, saddle-back search, KMP, Boyer-Moore, DFS, BFS, Greedy algorithm, Dynamic programming. There are two books influenced me most, one is ‘Purely functional data structure’ by Chris Okasaki, the other is ‘Introduction to algorithms’. Problems I always don’t have enough time in writing this book during the past 6 years. I am not a native speaker, the biggest problem is about English. It is lack of proof reading by native speakers. I used some result directly, if I had time, I should add more proof for those results. Future work Ideally, I think a serious algorithm book should be written in a stable environment. I planned to write this book in 10 years. But everything changes so fast in modern society. I experienced lay-offs once in 2012 due to Symbian business cut off, and now again in MS. I am not sure if I can continue this work. I think the best way is to open this book to the community. Some future work in my mind: • Proof reading and review • Provide answers to the exercises • Provide proof for the directly referenced result The whole manuscript is available at github: https://github.com/liuxinyu95/AlgoXY Best regards -- Larry, LIU Xinyu https://sites.google.com/site/algoxy/ https://github.com/liuxinyu95/AlgoXY *e*^(*π*i)+1 = 0

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