- Haskell-Cafe - Haskell.org

Stack lock issue
by Dominick Samperi 01 Oct '21

01 Oct '21

Hi, Stack install does its thing in some hashed directory under .stack-work by default, but I want to write to <package-root>/bin as part of the configure process. I'm trying to do this as follows: -- configure file contains: cd $(stack path --project-root) echo "..." > .bin/foo.sh cd - > cd <project-root> > stack install I'm doing this under Windows with the born shell in my path. Problem: the use of stack to find the project-root directory is blocked waiting for the outer stack to terminate! This may have something to do with Windows "Device or resource busy" lock. Is there a better way? Thanks, Dominick <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_cam…> Virus-free. www.avg.com <http://www.avg.com/email-signature?utm_medium=email&utm_source=link&utm_cam…> <#DAB4FAD8-2DD7-40BB-A1B8-4E2AA1F9FDF2>

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Cabal or stack in 2021 ?
by Alexis Praga 01 Oct '21

01 Oct '21

Hi, As an intermediate beginner, I've been back into Haskell for the last months for a small project, using stack as the building tool. Why stack ? A few years back, I learned that it was the "best" way to build projects to avoid "cabal hell", which I understood at the time as "managing dependencies with cabal is hard". As such, I've use stack since and have been quite happy with it. The only drawback is that building a project can be quite long. This is usually not a problem, except for writing Haskell scripts using shelly (for example), where the stack layout is a bit impractical for fast-paced development. A solution is to use `runghc` or a script interpreter [1]. However, I've seen some projects where cabal is used to build directly instead of cabal, so it looks like the situation improved. My question is this: in 2021, is there a reason to switch back to cabal ? Thanks, [1] https://www.fpcomplete.com/haskell/tutorial/stack-script/ -- Alexis Praga

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Re: [Haskell-cafe] Pattern guards seen in the wild?
by Anthony Clayden 01 Oct '21

01 Oct '21

Thank you all for the examples. Hehe real-world data structures are messy. Especially if dictated by systems utilities that don't care for functional programming. In the back of my mind is: do these idioms date from before there were pattern synonyms? Would matching to a pattern synonym give clearer code in the case branching? (Would it be worth declaring a synonym for just one usage?) There's only one of those examples where I feel expressing without the Pattern guard would be awkward. Tom's example 1., whose characteristics are: * There's a long straggly sequence of matchers; * With a particularly awkward branch in the middle, needing sub-analysis of a _component_ of the scrutinee, and only if such a component is present; * If the sub-analysis fails to match, the logic must unnest itself and resume matching at the next branch of the straggle. The awkward branch (slightly reformatted) is > (GET, [x]) | Just (path', mime) <- List.lookup x staticFiles > -> Just (StaticFile mime path') `staticFiles` is a module-wide variable, so matching is looking outside the scrutinee, therefore couldn't be expressed as a pattern synonym. The `lookup` might return a `Nothing`, so the inner pattern match could fail/this is doing more than a 'local binding' with `let`, which "always succeed" says the Language Report.

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Re: [Haskell-cafe] Haskell's "historical futurism" needs better writing, not better tools
by Anthony Clayden 01 Oct '21

01 Oct '21

Hi Michael, oh dear, oh dear, oh dear. The seeds of your confusion are very evident from your message. How to back you out of whatever deep rabbit-hole you've managed to get your head into? > ... Your average reader (already a programmer) would be better served by a comparative approach: Here's how to say something in a couple of other programming languages, here's how to say something roughly equivalent in Haskell -- BUT, here's how it's subtly different in Haskell. No. Just no. Haskell is not "subtly different" to (say) Java in the way that C++ or C# are different. (I'll leave others to judge how subtly different they are.) Haskell is dramatically and fundamentally different. You can't just 'translate' an algorithm from OOP to Haskell. Many newbies try, and there's many tales of woe on StackOverflow. Just No. I really don't know how you could have got any experience with Haskell and say "subtly". I suggest you unlearn everything you think you know about Haskell, and strike out in an entirely different direction. The best approach would be to spend a few days playing with lambda calculus. (That's what I did before tackling Haskell.) > (I've actually been curtly informed on the beginners' list -- yes, the beginner' list! -- that my problems of comprehension can be solved simply: "Learn lambda calculus.") Lambda calculus is an excellent place for beginners to start. What could be easier to learn? It's certainly easier than grokking a Turing machine; and much easier than Haskell: less than a handful of primitives yet can compute anything computable. > And since the concepts are seldom described in concrete enough and time-honored programming language terms (by comparison to other programming languages) I'm guessing that the concepts you're talking of simply don't correspond to anything in time-honoured (procedural) programming. Anybody writing about Haskell (including anybody writing the User Guide) assumes a base level of understanding of Haskell. You've clearly veered off the track and haven't yet reached base. Remember the User Guide builds on top of the Language Report. (On the point of 'time-honoured': lambda calculus is almost exactly the same age as Turing machines. The first well-known programming language using lambda-calculus ideas (LISP 1966) is almost exactly the same age as the first OOP language (Simula 1967). Which is the more time-honoured?) You do have a point that the terminology in Haskell is often mysterious > [SPJ said] F# had settled on the term "workflow" instead of "monad", and he felt this was wise. Yes many have yearned for a more warm-and-cuddly term than "monad". But the terminology barrier starts before that. Haskell typeclasses are not 'classes' in any sense recognisable from OOP. There are no objects, no hidden state, no destructive assignment. We might go back to February 1988 when a strawman for what became typeclasses used OVERLOAD/INSTANCE. AntC

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Re: [Haskell-cafe] Haskell's "historical futurism" needs better writing, not better tools
by Anthony Clayden 01 Oct '21

01 Oct '21

> Switching subtopics to the "Chirality" section, ... I take Ben's point (with which I agree) to be that "Chirality" is an even more obscure word than "Endomorphism". (Except perhaps in the realm of subatomic particle physics.) Grokking this material is hard enough without having to reach for a dictionary. If you mean 'left-biased' vs 'right-biased', or 'from-front' vs 'from-rear' or 'Cons-oriented' vs 'Snoc-oriented', say that. (And I'll be interested to see how anyone explains this without `fromList` jigging their elbow.) Now I can see Foldable structures are abstract, not spatial. But Cons is recursive on its (textually) right operand, whereas `Bin` or `Node` are symmetric between their (textually) left/right recursive operands. I guessed that's what the Chirality section was talking about, so I skimmed the first sentence and skipped on.

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Re: [Haskell-cafe] Pattern guards seen in the wild?
by Anthony Clayden 01 Oct '21

01 Oct '21

Thanks Viktor, you've answered (in the negative) one of my follow-on q's which was: isn't the comma just standing for Boolean `&&` ? > which would otherwise be something like: ... I would go: > smtpGreeting :: Int -> SmtpReply -> SmtpM B.ByteString > smtpGreeting _ r = > | replyCont r = pure B.empty > | code `div` 100 /= 2 = B.empty <$ modify' bail code > | otherwise = smtpSendHello > where > code = replyCode r > bail code s = > s { smtpErr = ProtoErr code $ replyText r } > but I find the pattern guard form to read "declarative", Hmm? Your `code <- ...` left-arrow doesn't look at all declarative to me. It's reminiscent of a binding in a do-block, or a 'source' in a comprehension. Strong imperative/sequential overtones. > with less "if then else" baggage and nesting getting in the way of seeing the essential conditions. My suggestion above also avoids "if then else". I guess a case of de gustibus ... To my taste, GHC Haskell is just too bloated/there's too many (equivalent) ways of writing code/there's too many idioms I have to keep up with to read code. It's not that there's anything particularly 'wrong' with any one of them; it's the sheer number of them. I'd have to say patterns/matching suffer a low power to weight ratio, where 'weight' means syntactic clutter and gotcha's: View pattern arrow-from-nowhere, I'm looking at you; pattern signatures double-forall's, empty forall's, double-constraints, I'm looking at you.

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canonicalization of interval libraries
by Olaf Klinke 29 Sep '21

29 Sep '21

Emily Pillmore wrote: > Hello Haskell! > > I'm pleased to announce that the Core Libraries Committee Elections for September 2021 have concluded, and we have selected 2 new CLC members: > > - [Andrew Lelechenko]( https://github.com/Bodigrim ) > > - [Melanie Brown]( https://github.com/bi-functor ) > I could not help but notice that both new members have either written or contributed to an interval library. There are a handful out there (disclaimer: I have written one of them) but as far as I know there is no de-facto standard. Why is that? Is it because the applications of intervals are too diverse and hence no single type fits all? Or is it because it is such a niche application that no single library could gather enough traction? I'm curious whether others see the need to have a de-facto standard interval library that is both general and performant, as we are used to from our "core libraries". Judging from the number of downloads on hackage, people are mostly interested in intervals of floating point numbers and intervals of time. Olaf P.S. Yes, I am aware of the relevant xkcd comic on standards.

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[ANN] CLC Elections Outcome - September 2021
by Emily Pillmore 29 Sep '21

29 Sep '21

Hello Haskell! I'm pleased to announce that the Core Libraries Committee Elections for September 2021 have concluded, and we have selected 2 new CLC members: - [Andrew Lelechenko]( https://github.com/Bodigrim ) - [Melanie Brown]( https://github.com/bi-functor ) The candidate pool was especially broad for this election and it was very difficult to choose, but we'd like to thank everyone for applying nonetheless. It is genuinely heartwarming to see so many people eager to help support the Haskell ecosystem in an official capacity! We encourage any and all candidates to continue helping to support the core libraries as we renovate the CLC. As mentioned in the latest CLC update (see: https://discourse.haskell.org/t/state-of-the-core-libraries-committee-updat… ), we are set to begin writing a new process and ways of working for the CLC now that the elections have concluded. We aim to have these finished within the month. Happy Hacking! Emily Pillmore - on behalf of the CLC

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Very binding semicolon
by Anthony Clayden 28 Sep '21

28 Sep '21

>From the department of improbable syntax/I don't get how this works, but it does: > f :: [a] -> [a] > ;; f xs = xs ++ reverse xs Nicely (to my eye) groups/indents the binding under the signature. Especially handy with ScopedTypeVariables, to show how the scoped vars 'belong' > f :: forall a. [a] -> [a] > ;; f xs = xs ++ ys > where > ys :: [a] > ys = reverse xs The doubled `;;` stands out like a ditto. It could be a single semicolon (which means there's an empty decl/binding between the semis -- I don't see that's allowed by the syntax). Unfortunately, for multi-line bindings you need to repeat the `;;` > f :: [a] -> [a] > ;; f [] = [] > ;; f xs = xs ++ reverse xs

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[TFP'22] first call for papers: Trends in Functional Programming 2022, 10-11 February (with Lambda Days 2022 & TFPIE 2022)
by Peter Achten 27 Sep '21

27 Sep '21

====== TFP 2022 ====== 23rd Symposium on Trends in Functional Programming 10-11 February, 2022 Krakow, Poland https://trendsfp.github.io/index.html == Important Dates == Submission deadline for pre-symposium review Wednesday 1st December, 2021 Submission deadline for draft papers Wednesday 12th January, 2022 Notification for pre-symposium submissions Friday 21st January, 2022 Notification for draft submissions Friday 21st January, 2022 Symposium dates Thursday 10th - Friday 11th February, 2022 Submission deadline for post-symposium reviewing Wednesday 16th March, 2022 Notification for post-symposium submissions Friday 13rd May, 2022 The Symposium on Trends in Functional Programming (TFP) is an international forum for researchers with interests in all aspects of functional programming, taking a broad view of current and future trends in the area. It aspires to be a lively environment for presenting the latest research results, and other contributions. Please be aware that TFP uses two distinct rounds of submissions. TFP 2022 will be co-located with two other functional programming events. TFP 2022 will be accompanied by the International Workshop on Trends in Functional Programming in Education (TFPIE), which will take place on February 11. Simultaneously with TFP, Lambda Days '22 is a two day conference where academia meets industry, where research and practical application collide. == Scope == The symposium recognizes that new trends may arise through various routes. As part of the Symposium's focus on trends we therefore identify the following five article categories. High-quality articles are solicited in any of these categories: * Research Articles: Leading-edge, previously unpublished research work * Position Articles: On what new trends should or should not be * Project Articles: Descriptions of recently started new projects * Evaluation Articles: What lessons can be drawn from a finished project * Overview Articles: Summarizing work with respect to a trendy subject Articles must be original and not simultaneously submitted for publication to any other forum. They may consider any aspect of functional programming: theoretical, implementation-oriented, or experience-oriented. Applications of functional programming techniques to other languages are also within the scope of the symposium. Topics suitable for the symposium include, but are not limited to: * Functional programming and multicore/manycore computing * Functional programming in the cloud * High performance functional computing * Extra-functional (behavioural) properties of functional programs * Dependently typed functional programming * Validation and verification of functional programs * Debugging and profiling for functional languages * Functional programming in different application areas: security, mobility, telecommunications applications, embedded systems, global computing, grids, etc. * Interoperability with imperative programming languages * Novel memory management techniques * Program analysis and transformation techniques * Empirical performance studies * Abstract/virtual machines and compilers for functional languages * (Embedded) domain specific languages * New implementation strategies * Any new emerging trend in the functional programming area If you are in doubt on whether your article is within the scope of TFP, please contact the TFP 2022 program chairs, Wouter Swierstra and Nicolas Wu. == Best Paper Awards == To reward excellent contributions, TFP awards a prize for the best paper accepted for the formal proceedings. TFP traditionally pays special attention to research students, acknowledging that students are almost by definition part of new subject trends. A student paper is one for which the authors state that the paper is mainly the work of students, the students are listed as first authors, and a student would present the paper. A prize for the best student paper is awarded each year. In both cases, it is the PC of TFP that awards the prize. In case the best paper happens to be a student paper, that paper will then receive both prizes. == Instructions to Author == Papers must be submitted at: https://easychair.org/conferences/?conf=tfp22 Authors of papers have the choice of having their contributions formally reviewed either before or after the Symposium. == Pre-symposium formal review == Papers to be formally reviewed before the symposium should be submitted before an early deadline and receive their reviews and notification of acceptance for both presentation and publication before the symposium. A paper that has been rejected in this process may still be accepted for presentation at the symposium, but will not be considered for the post-symposium formal review. == Post-symposium formal review == Draft papers will receive minimal reviews and notification of acceptance for presentation at the symposium. Authors of draft papers will be invited to submit revised papers based on the feedback received at the symposium. A post-symposium refereeing process will then select a subset of these articles for formal publication. == Paper categories == Draft papers and papers submitted for formal review are submitted as extended abstracts (4 to 10 pages in length) or full papers (20 pages). The submission must clearly indicate which category it belongs to: research, position, project, evaluation, or overview paper. It should also indicate which authors are research students, and whether the main author(s) are students. A draft paper for which all authors are students will receive additional feedback by one of the PC members shortly after the symposium has taken place. == Format == Papers must be written in English, and written using the LNCS style. For more information about formatting please consult the Springer LNCS web site. == Program Committee == Program Co-chairs Nicolas Wu - Imperial College London Wouter Swierstra - Utrecht University The remainder of the PC will be announced on the conference website.

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