- Haskell-Cafe - Haskell.org

Future of lucid
by Simon Jakobi 10 Jun '20

10 Jun '20

Hi! I recently noticed that the issue tracker for the lucid package at https://github.com/chrisdone/lucid has been disabled. Does this have any implications for the future maintenance of the package? Is anyone still committed to maintaining the package? (I've CC'd Oleg who made the most recent commit to the repo.) The context for my question is that we'd like to use lucid for the Dhall documentation generator that is being developed as a part of this year's GSoC. Thanks! Simon

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Re: [Haskell-cafe] Looking for a paper [Dijkstra-Dot]
by Anthony Clayden 10 Jun '20

10 Jun '20

> Richard O'Keefe wrote: > ... More seriously, in "f x", there is an explicit > operator already. It's "f". The space is needed for lexical > reasons only. If you say no, functions are not operators -- > though in Haskell infix operators are functions -- but > application is the operator, so you should write "f @ x <http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe>" (usual > FP notation) or "f.x" (Dijkstra), then although it isn't > technically true, I've always felt that there is an infinite > regress lurking in the background: > if x + y means (+) x y > which really stands for (+)@x @ <http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe> y > then shouldn't that in turn stand for (@)((@)(+)x)y > and what should _that_ stand for? Heh, heh there's another corner where Haskell semantics appears to give an infinite regress; and we have to suppose there's some internal magic that can't be expressed in the surface language: Report section 6.4.1 Numeric Literals. "An integer literal represents the application of the function `fromInteger` to the appropriate value of type `Integer`." OK. How do we write in Haskell that "appropriate value"? We could write `7 :: Integer` but that's shorthand for `(fromInteger #7#) :: Integer`, in which I've used `#7#` to denote the "appropriate value" doo-hickey. There's no way in Haskell to write a literal that's type `Integer`, except by invoking `fromInteger`. `(fromInteger (7 :: Integer)) :: Integer` ? Both the explicit and implicit `fromInteger` in there are no-ops. AntC

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Library maintainers: Include your library in CodeWorld web-based Haskell environment
by Chris Smith 10 Jun '20

10 Jun '20

Hello, I'm the maintainer of CodeWorld. In addition to the K-12 education uses, CodeWorld provides a web-based programming environment at http://code.world/haskell to write short snippets of Haskell and share it easily with others. I am trying to ensure that as many interesting Haskell libraries as possible are available on the platform. If you are interested in ensuring that a library is included, whether you're the maintainer or just am interested user, please take a look at the package list at https://github.com/google/codeworld/blob/master/codeworld-available-pkgs/co… Packages that fit here are: 1. No I/O, except for stdin/out/err. Since CodeWorld runs code in a web browser, there is no filesystem, for example. 2. Do not rely on native libraries, or have dependencies that do. This all depends on the library building with GHCJS. 3. Do not require use of Template Haskell by clients. It's okay if your package needs template Haskell to build, but people using your library via CodeWorld cannot yet use TH themselves. If you have a library you'd like to see included that's not in that list, please let me know, either with just an email or with a pull request at the GitHub link above. Thanks, Chris

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Generating PDF from HTML with Pandoc
by Geraldus 09 Jun '20

09 Jun '20

Hi dear Cafe! I'm trying to achieve trivial task to generate PDF from HTML template using Pandoc. So far I've tried `wkhtmltopdf` and `pdflatex` creators, both with no luck. I want to put few words about `pdflatex` and `xelatex` creators first, for someone who will struggle with same task in future, it's quite hard to find code examples on the web. Initially I wasn't able to render document with `pdflatex` creator. I would like to mention that `pdflatex` required a lot of LaTeX stuff to be installed, especially font packages. Also I've spent several hours to make rendering happen because I haven't specified template in `WriterOptions`. `pdflatex` do not capable to handle Cyrillic Unicode characters, and finally I figured out I have to use `xelatex` creator. Also I've found and used default template: > pandoc <- readHtml def (toStrict $ renderHtml html) > tpl' <- getDefaultTemplate "latex" > makePDF "xelatex" [] writeLaTeX (def {writerTemplate = Just tpl'}) pandoc But in this case I got white space instead of Cyrillic chars in resulting PDF and a bunch of warnings about missing chars in default font in console. I assume the font itself is specified in template. I've looked into default template and it's huge. I guess I can prepare more simple template for my own needs but it will take a lot of time to get familiar with LaTeX document syntax. I've tried `wkhtmltopdf`, which seems to be lightweight and easy solution. It seemed to work well except encoding issues: resulting PDF contains Cyrillic which rendered incorrectly. I've tried to pass `["encoding utf-8"]` as arguments in `makePDF` call, but this results in runtime error: > --margin-bottom specified in incorrect location Googling around this issue led me to glue that when I pass encoding argument to `wkhtmltopdf` it breaks expected arguments order in command which Pandoc generates. This is likely could be easily fixed, but Pandoc have a lot of opened issues on Github and also it requires some digging into `wkhtmltopdf` command line arguments syntax. I've looked into Pandoc sources and it seems possible to provide simple patch, but I need a guidance. According to `wkhtmltopdf` it distinguish global args, page args, cover args, table of contents args. `encoding` argument is page level argument, but Pandoc put extra args specified in `makePDF` after default page arguments (`pdfargs` in following code sample): > let args = mathArgs ++ concatMap toArgs > [("page-size", getField "papersize" meta') > ,("title", getField "title" meta') > ,("margin-bottom", Just $ fromMaybe "1.2in" > (getField "margin-bottom" meta')) > ,("margin-top", Just $ fromMaybe "1.25in" > (getField "margin-top" meta')) > ,("margin-right", Just $ fromMaybe "1.25in" > (getField "margin-right" meta')) > ,("margin-left", Just $ fromMaybe "1.25in" > (getField "margin-left" meta')) > ,("footer-html", getField "footer-html" meta') > ,("header-html", getField "header-html" meta') > ] ++ pdfargs Likely this breaks everything. The quickest and dirtiest workaround I see is to check each argument, and if it is a page level argument put it for each page object. Another solution may be to specify encoding for Pandoc document some other way, but I can't guess how to do that yet. Maybe someone have already faced similar task and knows easier way to render HTML to PDF with Haskell. I will very grateful for any help, advice or other glues how to achieve my goal. Arthur.

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Re: [Haskell-cafe] Looking for a paper [Dijkstra-Dot]
by Anthony Clayden 09 Jun '20

09 Jun '20

> Richard O'Keefe wrote: > This is one of the notational issues where I venture to disagree > with the Master. It's on a par with arguing that a number like > 1234 would be easier to read as 1`2`3`4 where the semantics of > x`y is x*10+y. Thanks Richard, and more to the point/dot: If dot means function application then `3.14` must be `3` applied to `14`. Or perhaps the Master expects Floats to be written European-style with commas? Good luck with that in Haskell. Let's also use Euro-style space as thousands separator! Or perhaps Dijkstra as more mathematician doesn't dirty his hands with Floats. Meta: all the above is tongue-in-cheek. AntC

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Re: [Haskell-cafe] Looking for a paper [Dijkstra-Dot]
by Anthony Clayden 09 Jun '20

09 Jun '20

>> On 6/5/20 7:05 AM, Anthony Clayden wrote: ... >>* Also it doesn't seem to know Haskellers very well; nor Dijkstra's *>>* well-known support for Haskell in education. *>> >>* There's other bits and pieces of 'Publications' on that the-magus site; *>>* including spoofs of Dijkstra which can't even spell his first name *>>* right. I rather suspect the ewd.pdf is a spoof that didn't turn out very *>>* funny. So altogether it's a couple of dudes shooting the breeze. * > These all seem pretty irrelevant to the point being made, which I think > has merit. (See my prev post about its lack of merit.) No Haskeller I've ever come across would accuse Dijkstra of "stick[ing] to the antiquated imperative paradigm". Dijkstra advocated teaching Haskell as an antidote to imperativism. EWD1300 is advocating for his own 'notational conventions', chiefly for writing math and formalising proofs. I don't see anything very specific to programming languages; certainly nothing specific to any paradigm. The pdf (words imputed to 'Haskeller') doesn't understand 'first-class': The term dates back to Strachey 1967; it's to do with semantics of names; what in a FP context we'd call 'referential transparency'. It has nothing to do with syntax. Column 2 of page 1 is bogus. Even if 'Haskeller' didn't know that CompSci archaeology, they'd certainly know the ($) operator. Whether or not it's the most important operator, there _is_ an operator and it is first-class. 'Haskeller' gets several answers wrong at the top of p2; finally gets to $ and gets that wrong too: EWD's question re `length $ [] = 0` is not a way to define `length`. Any Haskell beginner could stick that into an actual Haskell compiler and see why. Towards the bottom of p2 EWD admits "I do not know your Haskell very well ...". I'd say this faux-Haskeller knows Haskell less well than faux-EWD. Just before that admission is another piece of bogus notation for operator sections of `x * y`. None of that appears in EWD1300. > This is all just a language design curiosity to me, though, > and I'm not looking to start a new religious war until some of the > present ones are resolved. Well, don't look for pointers to language design from the couple of jokers portrayed in that pdf. I find it actually insulting to the good sense the real Dijkstra always showed; and insulting to Haskellers -- what's with all this gratuitous imputing of emotion? What's with just getting Haskell wrong? It's easy to check those claims; it's easy to get the (alleged) 'thought' peer-reviewed from the Haskell community. AntC

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Reminder: ZuriHac is happening (remotely) this weekend be great fun!
by Jasper Van der Jeugt 09 Jun '20

09 Jun '20

Hi everybody! This is a reminder that not only will ZuriHac be happening this year, but because it will be remote, the number of attendees has virtually no upper limit. We're quite excited (and a little bit nervous) to see how a remote event will play out. We will for sure lose a little bit of the magic feeling of hacking on projects together, however we hope that getting together online will still be a great experience. Another benefit is that people can join from all over the world, and that the event will generate a lot fewer CO2 emissions this year, so we can all feel good about ourselves! A brief summary of what will be there - Talks by Alexis King, Rob Rix, Gabriel Gonzalez, Philip Wadler and Simon Meier & Ognjen Marić will be live-streamed on our Youtube channel: <https://www.youtube.com/channel/UC2zfPMH_srjxUN5EYrfIhCw>. - Well-Typed will teach two advanced sessions, one about Datatype-Generic Programming and one about InfoSec and Haskell. - Julie Moronuki will teach a beginner track. - There is a GHC track with talks by Richard Eisenberg, Divesh Otwani, Facundo Dominguez and Nicolas Frisby. - Of course, lots of Haskell hacking and socialing! You can find all information & register on our website: <https://zfoh.ch/zurihac2020> Warm regards Jasper Van der Jeugt

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First call for draft papers for IFL 2020 (Implementation and Application of Functional Languages)
by Jurriaan Hage 08 Jun '20

08 Jun '20

Hello, Please, find below the final call for draft papers for IFL 2020. Please forward these to anyone you think may be interested. Apologies for any duplicates you may receive. best regards, Jurriaan Hage Publicity Chair of IFL ================================================================================ IFL 2020 32nd Symposium on Implementation and Application of Functional Languages venue: online 2nd - 4th September 2020 https://www.cs.kent.ac.uk/events/2020/ifl20/ ================================================================================ ### Scope The goal of the IFL symposia is to bring together researchers actively engaged in the implementation and application of functional and function-based programming languages. IFL 2020 will be a venue for researchers to present and discuss new ideas and concepts, work in progress, and publication-ripe results related to the implementation and application of functional languages and function-based programming. Topics of interest to IFL include, but are not limited to: - language concepts - type systems, type checking, type inferencing - compilation techniques - staged compilation - run-time function specialisation - run-time code generation - partial evaluation - (abstract) interpretation - meta-programming - generic programming - automatic program generation - array processing - concurrent/parallel programming - concurrent/parallel program execution - embedded systems - web applications - (embedded) domain specific languages - security - novel memory management techniques - run-time profiling performance measurements - debugging and tracing - virtual/abstract machine architectures - validation, verification of functional programs - tools and programming techniques - (industrial) applications ### Post-symposium peer-review Following IFL tradition, IFL 2020 will use a post-symposium review process to produce the formal proceedings. Before the symposium authors submit draft papers. These draft papers will be screened by the program chair to make sure that they are within the scope of IFL. The draft papers will be made available to all participants at the symposium. Each draft paper is presented by one of the authors at the symposium. After the symposium every presenter is invited to submit a full paper, incorporating feedback from discussions at the symposium. Work submitted to IFL may not be simultaneously submitted to other venues; submissions must adhere to ACM SIGPLAN's republication policy. The program committee will evaluate these submissions according to their correctness, novelty, originality, relevance, significance, and clarity, and will thereby determine whether the paper is accepted or rejected for the formal proceedings. We plan to publish these proceedings in the International Conference Proceedings Series of the ACM Digital Library, as in previous years. ### Important dates Submission deadline of draft papers: 17 August 2020 Notification of acceptance for presentation: 19 August 2020 Registration deadline: 31 August 2020 IFL Symposium: 2-4 September 2020 Submission of papers for proceedings: 7 December 2020 Notification of acceptance: 3 February 2021 Camera-ready version: 15 March 2021 ### Submission details All contributions must be written in English. Papers must use the ACM two columns conference format, which can be found at: http://www.acm.org/publications/proceedings-template ### Peter Landin Prize The Peter Landin Prize is awarded to the best paper presented at the symposium every year. The honoured article is selected by the program committee based on the submissions received for the formal review process. The prize carries a cash award equivalent to 150 Euros. ### Organisation IFL 2020 Chair: Olaf Chitil, University of Kent, UK IFL Publicity chair: Jurriaan Hage, Utrecht University, The Netherlands ### Virtual symposium Because of the Covid-19 pandemic, this year IFL 2020 will be an online event, consisting of paper presentations, discussions and virtual social gatherings. Registered participants can take part from anywhere in the world. ### Acknowledgments This call-for-papers is an adaptation and evolution of content from previous instances of IFL. We are grateful to prior organisers for their work, which is reused here.

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Re: [Haskell-cafe] Looking for a paper [Dijkstra-Dot]
by Anthony Clayden 08 Jun '20

08 Jun '20

> Ben Franksen wrote: >>* Well, don't look for pointers to language design from the couple of* >>* jokers portrayed in that pdf.* >> >>* I find it actually insulting to the good sense the real Dijkstra* >>* always showed; and insulting to Haskellers ...* > I really don't get why you're so upset about this harmless opinionated > piece that, in a humorous and obviously exaggerated way, It's not apparent to me this is humour, not even intended as humour. Notoriously, it's very difficult to get across sarcasm/irony on the interwebs. The tongue-in-cheek is not apparent to one of the authors, who has actually implemented these ideas blog.languager.org/2014/09/pugofer.html and it seems inflicted them on undergraduates. Including "8. layout is the only way to denote nesting ...". While they were at it, why not introduce sugar for function definition: > length . [] = 0 would be easy to desugar as an equation defining `length`. It's not apparent from the original thread May 2019 this is all a big hoot. If it's humour, who's the butt of the joke? A caricature of a Haskell newbie who doesn't understand Haskell, and can only regurgitate FP ideals as cheap dogma, played like a trout until "Exasperated". This is cruel sport, not Socratic method. Not humorous. > applies some of Dijkstra's ideas about programming language syntax ... It's not apparent to me that EWD1300 is about programming languages; the piece addresses "polite mathematics", name-checks Whitehead, Leibniz, Tarski -- who are not well-known for their work on programming languages. > Putting these words into Dijkstra's mouth is just an artist's freedom, If it's intended as art, the least they could do is put their name to it. > Despite your endless ranting the authors quite obviously do understand > EWD1300. That's not apparent to me either. > I also don't see how this has anything to do with Dijkstra promoting > Haskell for teaching. I'm not expecting the real Dijkstra would be uncritical of Haskell. I do expect that since Dijkstra saw Haskell's value for teaching, he would respect the (always difficult) design/syntax choices in the language. It's the faux-EWD's snide tripping-up of Haskeller that is uncharacteristic of Dijkstra. Also criticising Haskell's use of semicolon, which comes from ALGOL, as the real Dijkstra would be well aware. Also criticising allowing multiple constructs to express the same algorithm/semantics -- ALGOL also has plenty of that, and by design. And cheap shots about Haskell not supporting "assignments, pointers, gotos ..." -- we all know Dijkstra considers them harmful. AntC

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Re: [Haskell-cafe] Generalization of types during inference
by Olaf Klinke 08 Jun '20

08 Jun '20

> f 0 x = 0 > f 1 x = f 0 () > f n x = f (n-1) 'a' That's very interesting, I learned something new about GHC today. I used to believe that my Haskell compiler always type checks declarations on its own, and after that unifies its result with the type declaration that I provide. Polymorphic recursion yields a case where the compiler's inference procedure is evidently not independent of my provided type declaration. Can the above be abused to compile programs containing false type declarations? (It seems the answer is no, but maybe I lack the fantasy.) Thanks, Olaf

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