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type inference and FFI
by PICCA Frederic-Emmanuel 27 Oct '21

27 Oct '21

Hello, I have a bunch of C method that I need to call like this c'foo_unit16_t :: Ptr Word16 -> IO r c'foo_uint32_t :: Ptr Word32 -> IO r ... These methodes are called from a method like this process :: NativeType t => Dataframe t => IO r process df = do ... <pseudo code> case typeof t of WORD16 -> c'foo_unit16_t ... WORD32 -> c'foo_uint32_t ... Since there is type erasure, I would like to know what is the best way to write this process method. thanks for you help Frederic

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simple word processor
by Dennis Gaita 26 Oct '21

26 Oct '21

-1 <https://stackoverflow.com/posts/69702739/timeline> I am new to haskell and I need to create a simple word processor. It needs to read text from the cmd and implement functions that would edit functions found in the text so some other text.All functions in the text are odered. Each function i.e section,table,figures and ref must be located and numbered independently based on the order of occurence. Since tables and figures are within the sections function(just like a book), when a new section is encountered you will reset the value of tables and figures. So i did a loop where the tables and figures are inside the section loop when searching for the functions. The functions all start with this '' character (escape character) and must be replaced with text using this method: \Section{title}{id}: -> "Section n: title". Where n is the section number. \table{title}{id} : -> "Table n.m : title". Where n is the number of the last section encountered and m is the table number. And so on. I need help because my code isn't running.This is the code: import Text.Format import Data.Text.Internal.Search import Data.Text s = count . "section" -- count number of occurences of a certain word t = count . "table" f = count . "Figure" r = count . "ref" forLoop :: Int - Int - Int - Int forLoop s value = if i < s then forLoop (i + 1) format "Section{title}{id}" [show i, show {title}] then replace "Section{i}{title}" "Section {i}:{title}" else value forLoop t value = if j < t then forLoop (j + 1) format "table{title}{id}" [show i.j, show {title}] --change the text then replace "table{i}.{j}{title}" "Table {i}.{j} : {title}" else value forLoop f value = if k < f then forLoop (k + 1) format "figure{title}{id}" [show i.k, show {title}] --change the text then replace "Figure{title}{id}" "Figure {i}.{k} : {title}" else value if "ref{id}" == "table{title}" then forLoop r value = if l < r then forLoop (l + 1) format "ref{id}" [show {title}] --change the text then replace "ref{id}" "see {title} {i}.{j}" else value else Nothing if "ref{id}" == "Figure{title}" then forLoop r value = if m < r then forLoop (m + 1) format "ref{id}" [show {title}] --change the text then replace "ref{id}" "see {title} {i}.{m}" else value else Nothing if "ref{id}" == "Section{title}" then forLoop r value = if n < r then forLoop(n+1) format "ref{id}" [show{title}] then replace "ref{id}" "see {title} {i}" else value else nothing

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Numerics (was: Re: Trouble with asinh)
by Barak A. Pearlmutter 25 Oct '21

25 Oct '21

The numerics in Haskell have not been carefully vetted, for a variety of reasons. Not just under MS Windows, even under Linux. Here's an example: atan has drastic loss of precision in the imaginary direction around zero in the complex domain. $ ghci GHCi, version 8.8.4: https://www.haskell.org/ghc/ :? for help Prelude> :m + Data.Complex Prelude Data.Complex> tan (1e-20 :+ 0) 1.0e-20 :+ 0.0 Prelude Data.Complex> atan (1e-20 :+ 0) 1.0e-20 :+ (-0.0) Prelude Data.Complex> tan (0 :+ 1e-20) 0.0 :+ 1.0e-20 Prelude Data.Complex> atan (0 :+ 1e-20) 0.0 :+ (-0.0) Although there have been amazing efforts to use fancy PLT methods to improve the numerics of programs using source-to-source transformations and such, the boring janitorial work of checking and fixing numeric issues in the standard library doesn't seem to attract people. To be fair, it isn't my cup of tea either...

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[ANN] hslua 2.0.0, bridging Haskell and Lua
by Albert Krewinkel 23 Oct '21

23 Oct '21

I am pleased to announce the release of [HsLua] 2.0.0; a collection of packages offering (bidirectional) glue and abstractions bridging Haskell and Lua. HsLua is a featureful framework, enabling Haskell programmers to combine the embeddable scripting language Lua with code written Haskell. This new release is an almost complete rewrite and offers better performance, cleaner types, and adds more abstraction helpers. It supports exposing data and functions from Haskell to Lua in a convenient and structured way. Probably the best-known real world use case of HsLua is [pandoc], the universal document converter, where it serves as the central building block for [Lua filters] and custom writers. Contributions are welcome. [HsLua]: https://hslua.org [pandoc]: https://pandoc.org [Lua filters]: https://pandoc.org/lua-filters.html -- Albert Krewinkel GPG: 8eed e3e2 e8c5 6f18 81fe e836 388d c0b2 1f63 1124

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Munich Haskell Meeting, 2021-10-26 @ 19:30
by Leah Neukirchen 22 Oct '21

22 Oct '21

Dear all, next week, our monthly Munich Haskell Meeting will take place again on Tuesday, October 26 at Augustiner-Gaststätte Rumpler(!!) at 19h30. For details see here: http://muenchen.haskell.bayern/dates.html If you plan to join, please add yourself to this dudle until Tuesday 12:00 so we can reserve enough seats! 3G rules apply. It is OK to add yourself to the dudle anonymously or pseudonymously. https://dudle.inf.tu-dresden.de/haskell-munich-oct-2021/ Everybody is welcome! cu, -- Leah Neukirchen <leah(a)vuxu.org> https://leahneukirchen.org/

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unexpected compile error with wrapped HList
by Zoran Bošnjak 22 Oct '21

22 Oct '21

Hello members, I am struggling to compile the snippet below. GHC version is 8.10.4. If I try to construct the 'Variation' (with the type signature), I am getting an unexpected error. (see the comments in the code below). The error is only present if the HList is empty. I would appreciate a suggestion how to fix it. regards, Zoran --- {-# LANGUAGE DataKinds #-} {-# LANGUAGE GADTs #-} {-# LANGUAGE FlexibleContexts #-} {-# LANGUAGE FlexibleInstances #-} {-# LANGUAGE TypeOperators #-} {-# LANGUAGE PolyKinds #-} module Test where import Data.Kind data (a::k1) :<< (b::k2) infixr 5 :<< data HList (ts :: [Type]) where HNil :: HList '[] HCons :: x -> HList xs -> HList (x ': xs) data TVariation = TVariation1 | TVariation2 data Variation vt where Variation1 :: HList ts -> Variation ('TVariation1 :<< ts) Variation2 :: HList ts -> Variation ('TVariation2 :<< ts) -- This works as expected, including the explicit type signature. x1 :: Variation ('TVariation1 :<< '[()]) x1 = Variation1 (HCons () HNil) -- But the following 2 cases do not work as expected. -- 1. problem: -- This 'x0' type is inferred by GHC, -- but when specified as such, it won't compile. {- • Couldn't match type ‘k’ with ‘*’ ‘k’ is a rigid type variable bound by the type signature for: x0 :: forall k. Variation ('TVariation1 :<< '[]) at adhoc/test.hs:39:1-38 Expected type: Variation ((:<<) @TVariation @[k] 'TVariation1 ('[] @k)) Actual type: Variation ((:<<) @TVariation @[*] 'TVariation1 ('[] @*)) • In the expression: Variation1 HNil In an equation for ‘x0’: x0 = Variation1 HNil • Relevant bindings include x0 :: Variation ('TVariation1 :<< '[]) (bound at adhoc/test.hs:40:1) -} x0 :: Variation ('TVariation1 :<< '[]) x0 = Variation1 HNil class Empty t where mkEmpty :: t -- 2. problem: -- This instance declaration reports the same problem (as in x0 above). instance Empty (Variation ('TVariation1 :<< '[])) where mkEmpty = Variation1 HNil

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Downsides to disabling unticked-promoted-constructor warning?
by Markus Läll 21 Oct '21

21 Oct '21

Hi! Is there any consensus on unticked promoted constructors -- are they generally safe to use? Currently the warning is part of -Wall, but having promoted constructors unticked is just aesthetically nicer. Thanks, -- Markus Läll

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You're invited to the October virtual Haskell CoHack
by Chris Smith 19 Oct '21

19 Oct '21

Hi everyone, This Saturday, I’m once again hosting a virtual Haskell CoHack. In the past, we’ve had a great time with groups here working on various projects, whether it’s learning Haskell, hacking on GHC, writing documentation, making progress on personal projects, or just hanging out to chat with like-minded folk. You should consider coming if you would be excited to meet fellow Haskell programmers and work or learn together with them. There are details, including times, on the meetup page: https://www.meetup.com/NY-Haskell/events/280998863

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GDB and ticks
by Henning Thielemann 18 Oct '21

18 Oct '21

I am stepping through a Haskell program using the GNU debugger GDB and see function calls to handle_tick, handleProfTick, stopTicker all over the place. It sounds like they would manage profiling, but I compiled the executable without profiling.

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Looking for ESOP'22 AEC members
by Andreea Costea 18 Oct '21

18 Oct '21

For the first time since its foundation, ESOP will carry out an Artifact Evaluation process. The goal is to share with the community the research artefacts of papers accepted to its research track, acknowledging those works which have been rigorously implemented, tested and documented. To this purpose, we are looking for motivated students and postdocs to be members of the ESOP 2022 Artifact Evaluation Committee (AEC). The primary responsibility of an AEC member is to run the associated tools and confirm the results reported in the papers. If you know someone suitable for this role, please nominate them in the following form (or share the form with them for self-nomination): https://t.co/Jqa7edDqTg?amp=1 Come join us in this effort! Kind Regards, Andreea Costea and KC Sivaramakrishnan, AEC Co-Chairs of ESOP 2022

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