October 2021 - Glasgow-haskell-users

[ANNOUNCE] GHC 9.2.1 now available
by Ben Gamari 17 Nov '21

17 Nov '21

Hi all, The GHC developers are very happy to at long last announce the availability of GHC 9.2.1. Binary distributions, source distributions, and documentation are available at https://downloads.haskell.org/ghc/9.2.1 GHC 9.2 brings a number of exciting features including: * A native code generation backend for AArch64, significantly speeding compilation time on ARM platforms like the Apple M1. * Many changes in the area of records, including the new `RecordDotSyntax` and `NoFieldSelectors` language extensions, as well as Support for `DuplicateRecordFields` with `PatternSynonyms`. * Introduction of the new `GHC2021` language extension set, giving users convenient access to a larger set of language extensions which have been long considered stable. * Merging of `ghc-exactprint` into the GHC tree, providing infrastructure for source-to-source program rewriting out-of-the-box. * Introduction of a `BoxedRep` `RuntimeRep`, allowing for polymorphism over levity of boxed objects (#17526) * Implementation of the `UnliftedDataTypes` extension, allowing users to define types which do not admit lazy evaluation ([proposal]) * The new [`-hi` profiling] mechanism which provides significantly improved insight into thunk leaks. * Support for the `ghc-debug` out-of-process heap inspection library [ghc-debug] * Significant improvements in the bytecode interpreter, allowing more programs to be efficently run in GHCi and Template Haskell splices. * Support for profiling of pinned objects with the cost-centre profiler (#7275) * Faster compilation and a smaller memory footprint * Introduction of Haddock documentation support in TemplateHaskell (#5467) Finally, thank you to Microsoft Research, GitHub, IOHK, the Zw3rk stake pool, Tweag I/O, Serokell, Equinix, SimSpace, and other anonymous contributors whose on-going financial and in-kind support has facilitated GHC maintenance and release management over the years. Moreover, this release would not have been possible without the hundreds of open-source contributors whose work comprise this release. As always, do open a [ticket] if you see anything amiss. Happy testing, - Ben [apple-m1]: https://www.haskell.org/ghc/blog/20210309-apple-m1-story.html [proposal]: https://github.com/ghc-proposals/ghc-proposals/blob/master/proposals/0265-u… [-hi profiling]: https://well-typed.com/blog/2021/01/first-look-at-hi-profiling-mode/ [ghc-debug]: http://ghc.gitlab.haskell.org/ghc-debug/ [ticket]: https://gitlab.haskell.org/ghc/ghc/-/issues/new

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osx conundrum
by David Duke 14 Oct '21

14 Oct '21

I have a conundrum on which advice would be appreciate. Does anyone know how to successfully install ghc on OSX I've tried various binary instalation routes: macports, brew, direct binary downloads from haskel.org All have the same result. when I try to compile a basic hello world program I get Undefined symbols for architecture x86_64: "_iconv", referenced from: _hs_iconv in libHSbase-4.14.3.0.a(iconv.o) (maybe you meant: _base_GHCziIOziEncodingziIconv_iconvEncoding1_closure, _base_GHCziIOziEncodingziIconv_iconvEncoding1_info , _base_GHCziIOziEncodingziIconv_iconvEncoding4_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding15_info , _base_GHCziIOziEncodingziIconv_iconvEncoding4_info , _base_GHCziIOziEncodingziIconv_iconvEncoding7_info , _base_GHCziIOziEncodingziIconv_iconvEncoding6_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding6_info , _base_GHCziIOziEncodingziIconv_iconvEncoding8_info , _hs_iconv_open , _base_GHCziIOziEncodingziIconv_iconvEncoding9_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding12_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding11_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding9_info , _base_GHCziIOziEncodingziIconv_iconvEncoding12_info , _base_GHCziIOziEncodingziIconv_iconvEncoding13_info , _base_GHCziIOziEncodingziIconv_iconvEncoding11_info , _base_GHCziIOziEncodingziIconv_iconvEncoding7_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding_info , _base_GHCziIOziEncodingziIconv_iconvEncoding13_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding2_info , _base_GHCziIOziEncodingziIconv_iconvEncoding14_bytes , _base_GHCziIOziEncodingziIconv_iconvEncoding15_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding3_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding8_closure , _base_GHCziIOziEncodingziIconv_iconvEncoding2_closure , _hs_iconv , _base_GHCziIOziEncodingziIconv_iconvEncoding10_bytes , _hs_iconv_close , _base_GHCziIOziEncodingziIconv_iconvEncoding5_closure ) "_iconv_open", referenced from: _hs_iconv_open in libHSbase-4.14.3.0.a(iconv.o) (maybe you meant: _hs_iconv_open) "_iconv_close", referenced from: _hs_iconv_close in libHSbase-4.14.3.0.a(iconv.o) (maybe you meant: _hs_iconv_close) "_locale_charset", referenced from: _localeEncoding in libHSbase-4.14.3.0.a(PrelIOUtils.o) ld: symbol(s) not found for architecture x86_64 I've triedgiong through ghcup 8.8.4 8.6.5. 8.10.2 8.10.7 9.0.1 all have the same problem. I'd be happy to build from source. Small problem: what Haskell compiler do I use? Any advice on installs that works along with any changes to paths to avoid the iconv problems would be appreciated as currently my Haskell-related activities have come to a grinding halt. Switchig to a different OS would be nice but its not a feasible option a at present.Writing a compiler is starting to look attractive.. thanks David -- David Duke Emeritus Professor of Computer Science School of Computing University of Leeds UK E:duke.j.david@gmail.com W:https://engineering.leeds.ac.uk/staff/334/Professor_David_Duke

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Re: Glasgow-haskell-users Digest, Vol 212, Issue 5
by Dominic Steinitz 12 Oct '21

12 Oct '21

Hi David I am a long time user of ghc on OSX. I have seen that problem but never on native OSX only when using nix (and then I added it explicitly). Two things spring to mind: Add it explicitly on the compile command `-liconv` Use nix and then you can control the build environment in a totally controllable and reproducible manner. This is actually easier than it sounds: `curl https://nixos.org/nix/install | sh` and `nix-env -I ghc`. If you get the same error with that then we can try adding `iconv` explicitly. Dominic Steinitz dominic(a)steinitz.org http://idontgetoutmuch.org Twitter: @idontgetoutmuch > > I have a conundrum on which advice would be appreciate. Does > anyone know how to successfully install ghc on OSX > I've tried various binary instalation routes: > macports, brew, direct binary downloads from haskel.org > All have the same result. when I try to compile a basic hello world program > I get > > Undefined symbols for architecture x86_64: > "_iconv", referenced from: > > > I've triedgiong through ghcup > > 8.8.4 > 8.6.5. > 8.10.2 > 8.10.7 > 9.0.1 > > all have the same problem. > I'd be happy to build from source. Small problem: what Haskell compiler do > I use? > > Any advice on installs that works along with any changes to paths to avoid > the iconv problems would be appreciated as currently my Haskell-related > activities have come to a grinding halt. Switchig to a different OS would > be nice but its not a > feasible option a at present.Writing a compiler is starting to look > attractive.. > > thanks > David > > -- > David Duke > Emeritus Professor of Computer Science > School of Computing University of Leeds UK > E:duke.j.david@gmail.com > W:https://engineering.leeds.ac.uk/staff/334/Professor_David_Duke

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Pattern synonym constraints :: Ord a => () => ...
by Anthony Clayden 06 Oct '21

06 Oct '21

Thank you to Richard for the Tweag tutorials on Pattern Synonyms. That third one on Matchers was heavy going. I didn't find an answer (or did I miss it?) to something that's bugging me: > pattern SmartConstr :: Ord a => () => ... Seems to mean: * Required constraint is Ord a -- fine, for building * Provided constraint is Ord a -- why? for matching/consuming I'm using `SmartConstr` with some logic inside it to validate/build a well-behaved data structure. But this is an ordinary H98 datatype, not a GADT. I don't want to expose the datatype's underlying constructor, because client code could break the abstraction/build an ill-formed data structure. If I pattern-match on `SmartConstr`, the consuming function wants `Ord a`. But I can't always provide `Ord a`, because this isn't a GADT. And the client's function could be doing something that doesn't need `Ord a` -- like counting elements, or showing them or streaming to a List, etc. This feels a lot like one of the things that's wrong with 'stupid theta' datatype contexts. My work-round seems to be to define a second `ReadOnlyConstr` without constraints, that's unidirectional/ can't be used for building. For definiteness, the use case is a underlying non-GADT constructor for a BST > Node :: Tree a -> a -> Tree a -> Tree a > > pattern SmartNode :: Ord a => () => Tree a -> a -> Tree a -> Tree a with the usual semantics that the left Tree holds elements less than this node. Note it's the same `a` with the same `Ord a` 'all the way down' the Tree. If some function is consuming the Tree, it can provide constraints for its own purposes: > member :: Ord a => a -> Tree a -> Bool > dumbElem :: Eq a => a -> Tree a -> Bool > max :: Ord a => Tree a -> a (That again is the same thinking behind deprecating datatype contexts.) > countT (SmartNode l x r) = countT l + 1 + countT r -- why infer Ord a => ? > > class FancyShow t where > fancyShow :: Show a => Int -> t a -> String > instance FancyShow Tree where > fancyShow indent (SmartNode l x r) = ... -- rejected: Could not deduce Ord a > (Ref the parallel thread on Foldable: client code can't declare an instance for a Constructor class using SmartConstr.) I can see commonly your Provided would be at least the constraints inside the GADT constructor. But why presume I have a GADT? (And yes I get that a devlishly smart pattern might be building different GADT constrs/various constraints, so this is difficult to infer.) AntC

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