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by tech＠jimtyrerrobotics.ca 18 Oct '20

18 Oct '20

hello, I'm an industrial robot tech and the code I write seems to be composed of 99% side-effects ;-) That's the big dumb ones bolted to the floor that make cars and stuff. Decades of imperative sequence coding seem to have fossilized something in my brain. Trying to teach myself Haskell and going nowhere very slowly. Spent the last 8 weeks slowly plodding through "Real World Haskell" and "Learn you a Haskell" with the intention of re-writing a bash script in Haskell. I've normally learned programming by writing something I need instead of tutorials with which I seem to have an attention deficit problem. I use Linux for work and have written a bash script that uses bc and heredocs to write an .adoc file and then calls asciidoctor-pdf to generate an invoice. It's about 90 lines so I am not a scripting pro either. So typing './invoice Wk38' rolls a file called Wk38-of-2020-Invoice.pdf to send to clients. It was while writing this script that I stumbled upon pandoc and then Haskell. And that's where the trouble started. Tha abstraction and macro-approach of Haskell could provide a whole bag of tools for maintaining code (text files) on lines of multiple robots. About the existing script: I write plain text files on my phone that look like this: 14 Sep 0745 1600 Foo y 15 Sep 0815 1500 Foo y 16 Sep 0745 1400 Foo y 17 Sep 0745 1430 Foo y 18 Sep 0745 1400 Foo y and this one is called Wk38 and the fields are: |Date|Time In|Time Out|Proj|Lunch. Then I email it to myself and run the script. So I would be very grateful if someone could write some code for me and put my bootstraps in my fumbling hands: Get the name of the Wkxx file from the command line when running a Haskell standalone executable. fileName <- getArgs Load the lines of the file into a list of list of String[[]]. (or a better way?) lines <- fmap Text.lines (Text.readFile fileName) Recurse through each line of the list(s) and: *: Construct a date::String from the first two fields. (just a string, does not need a real "Date") *: Calc dailyElapsedTime::Double from difference between fields 4 and 3. *: Subtract 0.5hr lunch from dailyElapsedTime if field 6 == "y" *: Add dailyElapsedTime to accumlatedWeekTime::Double. *: Charge = If accumlatedWeekTime < 40hrs then multiply by rate1 *: elseif accumlatedWeekTime > 40hrs then multiply by rate2 *: Append |Date|Time In|Time Out|Charge|Project| to adoc file. If I could load it into ghci and step through it the lights may come on. Thanks very much Noodles

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Re: [Haskell-cafe] ANN: stack-2.5.1
by waldmann 17 Oct '20

17 Oct '20

> Doesn't compile for me GHC 8.10.2 when building using cabal [...] for stack-2.5.0.1, this worked: cabal install --constraint 'base16-bytestring==0.1.1.7' --constraint 'optparse-applicative==0.15.1.0' https://github.com/commercialhaskell/stack/issues/5298#issuecomment-7023387… NB : seems to me there's a whole recent-social-history-of-haskell essay waiting to be written around that question (build 'stack' with 'cabal'). - J.W.

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ANN: stack-2.5.1
by Emanuel Borsboom 15 Oct '20

15 Oct '20

See https://haskellstack.org/ for installation and upgrade instructions. **Changes since v2.3.3** Major changes: * Add the `snapshot-location-base` yaml configuration option, which allows to override the default location of snapshot configuration files. This option affects how snapshot synonyms (LTS/Nightly) are expanded to URLs by the `pantry` library. * `docker-network` configuration key added to override docker `--net` arg Behavior changes: * File watching now takes into account specified targets, old behavior could be restored using the new flag `--watch-all` [#5310](https://github.com/commercialhaskell/stack/issues/5310) Other enhancements: * `stack ls dependencies json` now includes fields `sha256` and `size` for dependencies of `type` `archive` in `location`. [#5280](https://github.com/commercialhaskell/stack/issues/5280) * Build failures now show a hint to scroll up to the corresponding section [#5279](https://github.com/commercialhaskell/stack/issues/5279) * Customisable output styles (see `stack --help` and the `--stack-colors` option, and `stack ls stack-colors --help`) now include `info`, `debug`, `other-level`, `secondary` and `highlight`, used with verbose output. Bug fixes: * Fix `stack test --coverage` when using Cabal 3 * `stack new` now generates PascalCase'd module name correctly. [#5376](https://github.com/commercialhaskell/stack/issues/5376) * Connection issues to Casa server no longer cause builds to failure. Casa acts only as an optimizing cache layer, not a critical piece of infrastructure. * Fix modified time busting caches by always calculating sha256 digest during the build process. [#5125](https://github.com/commercialhaskell/stack/issues/5125) **Thanks to all our contributors for this release:** * Andrea Condoluci * Andreas Herrmann * Andres Schmois * Ariel D. Moya Sequeira * Brandon Chinn * Cheah Jer Fei * DerpyCrabs * Emanuel Borsboom * Felix Yan * Jannik Theiß * Jens Petersen * Junji Hashimoto * Kirill Zaborsky * Michael Snoyman * Mihai Maruseac * Mike Pilgrem * Niklas Hambüchen * Ondřej Slámečka * Piper McCorkle * Thomas Lopatic * tomjaguarpaw

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Re: [Haskell-cafe] Overlapping instances: are functions and typeclass methods treated differently?
by Daniel Díaz 13 Oct '20

13 Oct '20

On Thu, Oct 8, 2020 at 2:12 PM Henning Thielemann < lemming(a)henning-thielemann.de> wrote: > > On Thu, 8 Oct 2020, Daniel Díaz wrote: > > > But now consider this instance: > > > > > newtype Wrapper a = Wrapper (Maybe a) > > > instance Show a => Show (Wrapper a) where > > > show (Wrapper x) = show x > > > > This compiles just fine, despite—to my mind—suffering from the exact > same problem that the "foo" function had. > > Why does it work? > > There is an instance Show (Maybe a) in Prelude, but no instance Show > (Wrapper a), so no overlapping. Sorry, I wasn't very clear there. The problem is not with the "Show (Wrapper a)" instance itself, but with its implementation of "show". It depends (just as the function "foo" did) on "Show (Maybe a)", for which there are overlapping instances. And yet "foo" compiles without problem, while the typeclass method doesn't.

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showing execution steps
by Luc Duponcheel 04 Oct '20

04 Oct '20

Hi, Is there a way to let ghci (or executable code generated by ghc) show all intermediate rewrite results when an expression is evaluated to its final result? Luc -- __~O -\ <, (*)/ (*) reality goes far beyond imagination

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ghc-9 needs type declaration where ghc-8 didn't (with RankNTypes)
by Johannes Waldmann 02 Oct '20

02 Oct '20

Dear Cafe, and thanks, Georgi, for answering my previous question here's another difference I noticed (based on real code, but reduced to a minimal test case) GHCi, version 9.0.0.20200925: https://www.haskell.org/ghc/ :? for help Prelude> :set -XRankNTypes Prelude> let f :: (forall a . a -> ()) -> () ; f = g ; g x = undefined <interactive>:2:43: error: • Couldn't match type ‘p0’ with ‘forall a. a -> ()’ Expected: (forall a. a -> ()) -> () Actual: p0 -> () Cannot instantiate unification variable ‘p0’ with a type involving polytypes: forall a. a -> () • In the expression: g In an equation for ‘f’: f = g The declaration is accepted by ghc-8. For ghc-9, I have to give a type signature for g (copy that of f), or replace `f = g` with `f x = g x`. - J.W.

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Novel error triggered building aeson on Mac
by Vanessa McHale 01 Oct '20

01 Oct '20

Hi all, I recently ran into the following interesting bug (reproducible on Mac; I used ghcup to install GHC and cabal-install): cabal unpack aeson-1.2.1.0 cabal build -w ghc-8.0.2 (yields this error log) Configuring library for aeson-1.2.1.0.. Preprocessing library for aeson-1.2.1.0.. Building library for aeson-1.2.1.0.. [ 1 of 23] Compiling Data.Attoparsec.Time.Internal ( attoparsec-iso8601/Data/Attoparsec/Time/Internal.hs, dist/build/Data/Attoparsec/Time/Internal.o ) [ 2 of 23] Compiling Data.Attoparsec.Time ( attoparsec-iso8601/Data/Attoparsec/Time.hs, dist/build/Data/Attoparsec/Time.o ) [ 3 of 23] Compiling Data.Aeson.Types.Internal ( Data/Aeson/Types/Internal.hs, dist/build/Data/Aeson/Types/Internal.o ) [ 4 of 23] Compiling Data.Aeson.Types.Generic ( Data/Aeson/Types/Generic.hs, dist/build/Data/Aeson/Types/Generic.o ) [ 5 of 23] Compiling Data.Aeson.Parser.UnescapePure ( pure/Data/Aeson/Parser/UnescapePure.hs, dist/build/Data/Aeson/Parser/UnescapePure.o ) [ 6 of 23] Compiling Data.Aeson.Parser.Unescape ( Data/Aeson/Parser/Unescape.hs, dist/build/Data/Aeson/Parser/Unescape.o ) [ 7 of 23] Compiling Data.Aeson.Parser.Time ( Data/Aeson/Parser/Time.hs, dist/build/Data/Aeson/Parser/Time.o ) [ 8 of 23] Compiling Data.Aeson.Parser.Internal ( Data/Aeson/Parser/Internal.hs, dist/build/Data/Aeson/Parser/Internal.o ) <command line>: can't load .so/.DLL for: /Users/vmchale/.cabal/store/ghc-8.0.2/lib/libHStm-lcl-cmpt-0.1.1.5-83154f89-ghc8.0.2.dylib (dlopen(/Users/vmchale/.cabal/store/ghc-8.0.2/lib/libHStm-lcl-cmpt-0.1.1.5-83154f89-ghc8.0.2.dylib, 5): REBASE_OPCODE_SET_SEGMENT_AND_OFFSET_ULEB has segment 2 which is not a writable segment (__LINKEDIT) in /Users/vmchale/.cabal/store/ghc-8.0.2/lib/libHStm-lcl-cmpt-0.1.1.5-83154f89-ghc8.0.2.dylib) Seems to be new; I guess the past libraries didn’t trigger it? I can’t tell if it’s a cabal-install bug, GHC bug, mac novelty… Cheers, Vanessa McHale

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ghc-9 strictness annotations change?
by Johannes Waldmann 01 Oct '20

01 Oct '20

Dear Cafe, did something change w.r.t. placement of the bang? GHCi, version 9.0.0.20200925: https://www.haskell.org/ghc/ :? for help Prelude> data T = T { foo :: ! Int } <interactive>:1:21: error: Operator applied to too few arguments: ! Prelude> data T = T { foo :: !Int } Prelude> - J.W.

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Re: [Haskell-cafe] I think I discovered my first Monoid instance
by David Banas 30 Sep '20

30 Sep '20

> > But we're talking about xor for the Word64 type, so it is slightly more > complicated to prove that it has a unit. Here's a proof in Agda: -- Agda proof that zero is the unit (i.e. - left and right identity) -- for the XOR operation. import Relation.Binary.PropositionalEquality as Eq open Eq using (_≡_; refl; cong; sym) open import Data.Nat using (ℕ; zero; suc; _+_; _*_; _∸_; _^_) -- Binary data. data Bin : Set where ⟨⟩ : Bin _O : Bin → Bin _I : Bin → Bin _xor_ : Bin → Bin → Bin ⟨⟩ xor y = y (x O) xor ⟨⟩ = x O (x O) xor (y O) = (x xor y) O (x O) xor (y I) = (x xor y) I (x I) xor ⟨⟩ = x I (x I) xor (y O) = (x xor y) I (x I) xor (y I) = (x xor y) O lemma : ∀ (b : Bin) ------------ → b xor ⟨⟩ ≡ b lemma ⟨⟩ = refl lemma (b O) = refl lemma (b I) = refl _ : ( ⟨⟩ I O O I O I I O ) xor ( ⟨⟩ O I I I O O O O ) ---------------------- ≡ ( ⟨⟩ I I I O O I I O ) _ = refl -- Left & right identity proofs. postulate binO : (⟨⟩ O) ≡ ⟨⟩ -- Just accomodating a syntactical nuisance. xor-idₗ : ∀ (b : Bin) ---------------- → (⟨⟩ O) xor b ≡ b xor-idₗ ⟨⟩ rewrite binO = refl xor-idₗ (b O) = refl xor-idₗ (b I) = refl xor-idᵣ : ∀ (b : Bin) ---------------- → b xor (⟨⟩ O) ≡ b xor-idᵣ ⟨⟩ rewrite binO = refl xor-idᵣ (b O) rewrite lemma b = refl xor-idᵣ (b I) rewrite lemma b = refl -db

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Re: [Haskell-cafe] [Haskell] [ANNOUNCE] Glasgow Haskell Compiler 9.0.1-alpha1 released
by Dan Burton 29 Sep '20

29 Sep '20

That's great news! Thank you for your hard work. Does this address the Windows issue with GHC 8.10.2? Will there still be a GHC 8.10.3 release? See: https://gitlab.haskell.org/ghc/ghc/-/issues/18550 (Pardon the dupe; I had the wrong address on haskell-cafe) -- Dan Burton On Tue, Sep 29, 2020 at 5:23 PM Dan Burton <danburton.email(a)gmail.com> wrote: > That's great news! Thank you for your hard work. > > Does this address the Windows issue with GHC 8.10.2? Will there still be a > GHC 8.10.3 release? > See: https://gitlab.haskell.org/ghc/ghc/-/issues/18550 > > -- Dan Burton > > > On Mon, Sep 28, 2020 at 3:16 PM Ben Gamari <ben(a)well-typed.com> wrote: > >> Hello all, >> >> The GHC team is very pleased to announce the availability of the first >> alpha release in the GHC 9.0 series. Source and binary distributions are >> available at the usual place: >> >> https://downloads.haskell.org/ghc/9.0.1-alpha1/ >> >> This first alpha comes quite a bit later than expected. However, we have >> done a significant amount of testing on this pre-release and therefore >> hope to be able to move forward quickly with a release candidate next >> week and with a final release in mid-October. >> >> GHC 9.0.1 will bring a number of new features: >> >> * A first cut of the new LinearTypes language extension [1], allowing >> use of linear function syntax and linear record fields. >> >> * A new bignum library (ghc-bignum), allowing GHC to be more easily >> used with integer libraries other than GMP. >> >> * Improvements in code generation, resulting in considerable >> performance improvements in some programs. >> >> * Improvements in pattern-match checking, allowing more precise >> detection of redundant cases and reduced compilation time. >> >> * Implementation of the "simplified subsumption" proposal [2] >> simplifying the type system and paving the way for QuickLook >> impredicativity in GHC 9.2. >> >> * Implementation of the QualifiedDo extension [3], allowing more >> convenient overloading of `do` syntax. >> >> * Improvements in compilation time. >> >> And many more. See the release notes [4] for a full accounting of the >> changes in this release. >> >> Do note that there are a few things that we expect will change before >> the final release: >> >> * We expect to sort out a notarization workflow for Apple Darwin, >> allowing our binary distributions to be used on macOS Catalina >> without hassle. >> >> Until this has been sorted out Catalina users can exempt the >> current macOS binary distribution from the notarization requirement >> themselves by running `xattr -cr .` on the unpacked tree before >> running `make install`. >> >> * We will likely transition the Alpine binary distribution to be fully >> statically-linked, providing a convenient, distribution-independent >> packaging option for Linux users. >> >> * We will be merging a robust solution for #17760 which will introduce >> a new primitive, `keepAlive#`, to the `base` library, subsuming >> most uses of `touch#`. >> >> As always, do test this release and open tickets for whatever issues you >> encounter. To help with this, we will be publishing a blog post >> describing use of our new `head.hackage` infrastructure to ease testing >> of larger projects with Hackage dependencies later this week. >> >> Cheers, >> >> - Ben >> >> >> [1] >> https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0111-l… >> [2] >> https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0287-s… >> [3] >> https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0216-q… >> [4] >> https://downloads.haskell.org/ghc/9.0.1-alpha1/docs/html/users_guide/9.0.1-… >> _______________________________________________ >> Haskell mailing list >> Haskell(a)haskell.org >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell >> >

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