December 2021 - Haskell-Cafe

Error message??
by Gregory Guthrie 15 Dec '21

15 Dec '21

I don't understand the error here: -- ------------------------------------------ -- Find permutation by index iPerm :: Int -> [a] -> (Int,Int) iPerm k list = nPerm k $ length list where nPerm k n = divMod k (fact(n - 1)) -- indexPerm :: Int -> [a] -> [a] indexPerm _ [] = [] indexPerm g list = d :: indexPerm r (delete d list) -- line 19 *** where (q,r) = iPerm g list d = list !! q Adding a type signature for indexPerm changes the error (below), but seems to be the same basic issue. I thought I might need: indexPerm :: Eq a => Int -> [a] -> [a] to match the restriction on delete argument types, although I would have thought that would be inferred if needed, but it gives the same error message. ----------------------------------------------------------------------- Prelude> (compiling) [1 of 1] Compiling Main ( syntaxtest.hs, interpreted ) yntaxtest.hs:19:20: error: * Couldn't match expected type `indexPerm r (delete1 d1 list1)' with actual type `a' because type variables `indexPerm', `r', `delete1', `d1', `list1' would escape their scope These (rigid, skolem) type variables are bound by an expression type signature: forall (indexPerm :: * -> * -> *) r (delete1 :: * -> * -> *) d1 list1. indexPerm r (delete1 d1 list1) at syntaxtest.hs:19:25-51 * In the expression: d :: indexPerm r (delete d list) In an equation for `indexPerm': indexPerm g list = d :: indexPerm r (delete d list) where (q, r) = iPerm g list d = list !! q * Relevant bindings include d :: a (bound at syntaxtest.hs:21:10) list :: [a] (bound at syntaxtest.hs:19:13) indexPerm :: Int -> [a] -> [delete d list] (bound at syntaxtest.hs:18:1) | 19 | indexPerm g list = d :: indexPerm r (delete d list) | ^ | 19 | indexPerm g list = d :: indexPerm r (delete d list) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Failed, no modules loaded. ----------------------------------------------------------------------- (error with the explicit type signature) syntaxtest.hs:19:20: error: * Couldn't match expected type `indexPerm r (delete d list)' with actual type `a' `a' is a rigid type variable bound by the type signature for: indexPerm :: forall a. Int -> [a] -> [a] at syntaxtest.hs:17:1-30 * In the expression: d :: indexPerm r (delete d list) In an equation for `indexPerm': indexPerm g list = d :: indexPerm r (delete d list) where (q, r) = iPerm g list d = list !! q * Relevant bindings include d :: a (bound at syntaxtest.hs:21:10) list :: [a] (bound at syntaxtest.hs:19:13) indexPerm :: Int -> [a] -> [a] (bound at syntaxtest.hs:18:1) | 19 | indexPerm g list = d :: indexPerm r (delete d list) | ^ | 19 | indexPerm g list = d :: indexPerm r (delete d list) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Failed, no modules loaded. Gregory Guthrie

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Fully (UK Home) Funded PhD Positions in the Safety and Security of Advanced Systems Group (Exeter, UK, Deadline 2021-01-24)
by Achim D. Brucker 15 Dec '21

15 Dec '21

Several fully funded PhD scholarships for UK applicants are available in the Security and Trust of Advanced Systems Group [1] (Prof. Achim Brucker [2] and Dr. Diego Marmsoler [3]) at the Department of Computer Science of the University of Exeter, UK [4]. We are looking for enthusiastic and outstanding Computer Science or Mathematics students with a strong background in at least one of the following topics: * safety or security of (software) systems, * formal modelling or formal reasoning/verification, * program analysis or program verification, * language-based security * semantics of programming languages, * theorem proving, model checking, * cryptographic protocols, * distributed systems (e.g., blockchain), * specification-based testing, and * design and implementation of security architectures. This award provides annual funding to cover UK tuition fees and a tax-free stipend. For students who pay UK tuition fees the award will cover the tuition fees in full, plus at least £15,009 per year tax-free stipend. The studentship will be awarded on the basis of merit for 3.5 years of full-time study. Interested candidates should contact the potential supervisors Prof. Achim Brucker (a.brucker(a)exeter.ac.uk) or Dr. Diego Marmsoler (d.marmsoler(a)exeter.ac.uk) to discuss their application. For more details, please consult the official advertisements: * Compositional Verification of Smart Contracts in Isabelle: https://www.exeter.ac.uk/study/funding/award/?id=4326 * Formal Verification for Safety- or Security-Critical Systems: https://www.exeter.ac.uk/study/funding/award/?id=4328 * Software Engineering for Security- or Safety-Critical Systems: https://www.exeter.ac.uk/study/funding/award/?id=4329 * Open Call: https://www.exeter.ac.uk/study/funding/award/?id=4343 The closing date for applications is midnight on the 24th of January 2022. Best, Achim and Diego [1] http://emps.exeter.ac.uk/computer-science/research/cyber-security/ [2] https://www.brucker.ch/ [3] https://marmsoler.com/ [4] http://emps.exeter.ac.uk/computer-science/ -- Prof. Achim Brucker | Chair in Cybersecurity & Head of Group | University of Exeter https://www.brucker.ch | https://logicalhacking.com/blog @adbrucker | @logicalhacking

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Postdoc position - hardware acceleration of Haskell
by Rob Stewart 14 Dec '21

14 Dec '21

Hi haskell-cafe, I have an opening for a postdoc position at Heriot-Watt University in Edinburgh, on hardware acceleration of functional programming languages. In particular, Haskell. Candidates should have a background in hardware design and FPGA programming. Hardware engineering experience should include circuit design, developing processor architectures, memory hierarchies and/or instruction sets. Candidates should have some understanding of functional programming. Programming language implementation experience is desirable, but not essential. The role will involve developing a special purpose processor for Haskell, aimed at outperforming the throughput and energy performance of CPUs. The project has close industry ties in Ireland and the Netherlands. It is a three year project, starting in May 2022. The HAFLANG project: https://haflang.github.io Job details and application form: https://enzj.fa.em3.oraclecloud.com/hcmUI/CandidateExperience/en/sites/CX/j… The application deadline is 28th February 2022. Contact the PI, Rob Stewart, with inquiries (R.Stewart(a)hw.ac.uk) Please share this widely. -- Rob Stewart Assistant Professor of Computer Science Heriot-Watt University, Edinburgh W: https://www.macs.hw.ac.uk/~rs46

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[CFP] Functional Conf 2022 online - have you got Haskell insights to share with the community?
by John Sinclair 13 Dec '21

13 Dec '21

Have you devised an innovative or novel application of Haskell? Have you solved a tricky problem using FP? This is a great opportunity to share what you've been working on. If it's related to functional programming, Functional Conf would love to hear from you! We are looking for deep technical topics related to Functional Programming. Learn more and submit your proposal here: https://confng.in/oVspOYAc <https://llink.to/?u=https:%2F%2Fsignal2domain.online%2Fclick%3Fredirect%3Dh…> Submissions close: 15 Jan 2022 Functional Conf is Asia's premiere functional programming conference. The event runs 24-26 March 2022 and due to COVID uncertainties will be held online. Over the course of 3 days, you'll get cutting edge insights from global thought leaders, practitioners and developers from prominent FP languages (this could be you!). At our last conference Edward Kmett who chairs the Haskell core libraries committee presented. The conference is designed to help attendees: - Understand the fundamental concepts of FP - Learn how others are leveraging FP to solve real world problems - Explore practical usages and gotchas in FP concepts from experts - Exchange real-world experience with your programing peers If you are just getting started with FP or work with it everyday, you'll love Functional Conf 2022! Here's a short video of past speakers sharing a little of their experience at Functional Conf: https://confng.in/EFX1sthg <https://llink.to/?u=https:%2F%2Fsignal2domain.online%2Fclick%3Fredirect%3Dh…> Submit your proposal here: https://confng.in/JzhW9cSX <https://llink.to/?u=https:%2F%2Fsignal2domain.online%2Fclick%3Fredirect%3Dh…> Hope to see you there! Best regards, John Sinclair and the Functional Conf Team

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ImplicitParams in GHC 9.0.1
by ☂Josh Chia (謝任中) 13 Dec '21

13 Dec '21

Hi, I have the following code that builds successfully with "stack build" under GHC 8.10.7 but fails to build under GHC 9.0.1: https://github.com/jchia/ip-bug The compiler is switched by commenting/uncommenting the compiler line in stack.yaml. GHC 9.0.1 gives me the error I paste at the end. Is this expected (maybe as part of "simplified subsumtion" in https://gitlab.haskell.org/ghc/ghc/-/wikis/migration/9.0#compiler-changes)? If so, how can the code be fixed? If not, is it a compiler bug? (This problem came up while using gi-gtk-3.0.38, where implicit params are used a lot). Josh /home/jchia/gh/ip-bug/src/Lib.hs:10:28: error: • Couldn't match type ‘(?self::Int) => Char’ with ‘Char’ Expected: Int -> Char -> Char Actual: Int -> ((?self::Int) => Char) -> Char • In the expression: foo In the expression: (let ?self = x in foo) :: Int -> Char -> Char In the expression: ((let ?self = x in foo) :: Int -> Char -> Char) x | 10 | bar x = ((let ?self = x in foo) :: Int -> Char -> Char) x | ^^^ /home/jchia/gh/ip-bug/src/Lib.hs:13:26: error: • Couldn't match type ‘(?self::Int) => Char’ with ‘Char’ Expected: Char -> Char Actual: ((?self::Int) => Char) -> Char • In the expression: foo x In the expression: let ?self = x in foo x In an equation for ‘baz’: baz x = let ?self = x in foo x | 13 | baz x = let ?self = x in foo x | ^^^^^

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DataKinds and Data.Char
by Olaf Klinke 13 Dec '21

13 Dec '21

Dear Café, Question: Is DataKinds promotion of Char values possible, and if yes, how? I want to define a data type of text where a certain character has special meaning. I could say: data SpecialText = SpecialText Char Text but it would be favourable if the type system forbids combining texts with distinct special characters. data SpecialText char = SpecialText Text Ideally, we could use DataKinds to specialize the char phantom type parameter to a promoted Char value, but neither 'x' nor ''x' is accepted by GHC, presumably for good reasons. After all, 'x' is syntactic sugar for the real constructor of a Char value (which is what? Data.Data.toConstr 'x' yields 'x'.) One certainly can define data types symbolizing selected single Char values to use as the phantom type, but that means the library author decides which Chars the user can declare as special. Thanks Olaf

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GHC debug plugin
by Daneel Yaitskov 12 Dec '21

12 Dec '21

Hi, I would like to enable stack traces at launch time and run program without HasCallStack overhead by default. I've got an idea to use GHC plugin which would duplicate all functions in modules with specified prefix. Duplicated functions should get disambiguating prefix (e.g. "debug") and HasCallStack constraint. Bodies of prefixed functions should be rewritten to use prefixed functions from matching modules (should be easy to do - hook just after renaming GHC phase when all names are fully qualified?). This way main function could choose "runLib" or "debugRunLib". Did anybody make something similar? -- Best regards, Daniil Iaitskov

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Re: [Haskell-cafe] Wiki account request
by howard.b.golden＠gmail.com 12 Dec '21

12 Dec '21

Hi Hyeon, I have created your Haskell wiki account. You should receive a temporary password by separate email. Please let me know if you have any problems. Regards, Howard On Mon, 2021-12-13 at 06:05 +0900, 김지현 wrote: > Hi folks, > > I'd like to create a new haskell wiki account with a username > "simnalamburt". At first, I tried to send an email to the "wiki- > account-request" mailing list as written in > https://wiki.haskell.org/index.php?title=Special:UserLogin, but I > couldn't find the mailing list. If that mailing list is gone, I think > the notice in the login page should be updated. > > If creating a wiki account takes a long time, can anyone do me a > favor? I just want to change the outdated link "Using haskell- > language-server with Vim or NeoVim." in the > https://wiki.haskell.org/Vim page to point to > https://haskell-language-server.readthedocs.io/en/latest/configuration.html… > . > > Best, > Hyeon Kim

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Priority queue benchmarks
by David Feuer 10 Dec '21

10 Dec '21

I've started working on performance of the venerable but somewhat neglected pqueue package. The changes I've made so far are pretty obviously good, and make a big difference in even the most informal testing. But to make decisions about smaller points, I really need benchmarks, and the package has none. Does anyone know of a benchmark suite for priority queues? One that includes algorithms that involve persistent queue use would be particularly desirable, but I'll take anything.

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Call for Workshop Proposals: ICFP 2022
by Ilya Sergey 08 Dec '21

08 Dec '21

CALL FOR WORKSHOP AND CO-LOCATED EVENT PROPOSALS ICFP 2022 27th ACM SIGPLAN International Conference on Functional Programming September 11 - 16, 2022 Ljubljana, Slovenia https://icfp22.sigplan.org/ The 27th ACM SIGPLAN International Conference on Functional Programming will be held in Ljubljana, Slovenia on September 11 - 16, 2022, with the option of virtual participation. ICFP provides a forum for researchers and developers to hear about the latest work on the design, implementations, principles, and uses of functional programming. Proposals are invited for workshops (and other co-located events, such as symposiums) to be affiliated with ICFP 2022 and sponsored by SIGPLAN. These events should be less formal and more focused than ICFP itself, include sessions that enable interaction among the attendees, and foster the exchange of new ideas. The preference is for one-day events, but other schedules can also be considered. The workshops are scheduled to occur on September 11th (the day before ICFP) and September 15-16th (the two days after ICFP). ---------------------------------------------------------------------- Submission details Deadline for submission: December 24, 2021 Notification of acceptance: January 10, 2022 Prospective organizers of workshops or other co-located events are invited to submit a completed workshop proposal form in plain text format to the ICFP 2022 workshop co-chairs (Arthur Azevedo de Amorim and Zoe Paraskevopoulou) via email to icfp-workshops-2022(a)googlegroups.com by December 24, 2021. (For proposals of co-located events other than workshops, please fill in the workshop proposal form and just leave blank any sections that do not apply.) Please note that this is a firm deadline. Organizers will be notified if their event proposal is accepted by January 10, 2022, and if successful, depending on the event, they will be asked to produce a final report after the event has taken place that is suitable for publication in SIGPLAN Notices. The proposal form is available at: http://www.icfpconference.org/icfp2022-files/icfp22-workshops-form.txt Further information about SIGPLAN sponsorship is available at: http://www.sigplan.org/Resources/Proposals/Sponsored/ ---------------------------------------------------------------------- Selection committee The proposals will be evaluated by a committee comprising the following members of the ICFP 2022 organizing committee, together with the members of the SIGPLAN executive committee. Workshop Co-Chair: Arthur Azevedo de Amorim (Boston University) Workshop Co-Chair: Zoe Paraskevopoulou (Northeastern University) General Chair: Andrej Bauer (University of Ljubljana) Program Chair: Zena Ariola (University of Oregon) ---------------------------------------------------------------------- Further information Any queries should be addressed to the workshop co-chairs (Arthur Azevedo de Amorim and Zoe Paraskevopoulou), via email to icfp-workshops-2022(a)googlegroups.com.

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