- Haskell-Cafe - Haskell.org

Re: [Haskell-cafe] (Feeling that) GHCi is trying to protect me from myself with overlapping instances and existential types
by Olaf Klinke 16 Feb '20

16 Feb '20

> the ones at Stack > Overflow basically told me that it does to "protect me from being too > dumb and not understanding my own code", the way I interpret it. I > felt that was totally against the principles of Haskell On the contrary! Protecing me against writing dumb code is one of the things where Haskell shines, and I am infinitely grateful for that. > Having GHCi protect me from that highly hypothetical situation while > preventing me from compiling theoretically correct programs seems > strange at best. But those theoretically correct programs may suddenly cease to be correct in very mysterious and little hypothetical ways, as explained below. I agree with Arien. Making the semantics of a function dependent on how many type class instances are in scope is totally against the principles of Haskell, IMHO. Even worse the function signature of createBar does not mention Class1 so at first glance there is no hint that type classes are at work here. Type class instances are hard to contain, in the sense that there is currently no mechanism of selectively importing or not importing them from some module. Change in semantics through orphan instances would be a nightmare to debug: Suppose you have written a package that defines Class1 and only the first incoherent instance. Alice comes along and uses your package to define a function useFoo :: Monoid a => a -> Either a a useFoo = foo and henceforth Alice relies on the semantics useFoo a = Right (a <> a), because that's what your package intends. Alice's code also depends on a package written by Bob, but she only uses some part of that package which is totally unrelated to useFoo and Class1. In an update of his package, Bob defines your second Class1 instance as orphan instance. Alice never explicitly imported any Class1 stuff from Bob's module, but the new instance will leak anyways. Suddenly the semantics of Alice's function changes, she gets useFoo a = Left a without any changes in her own code! If Bob did not adhere to the versioning policy then Alice has little chance of knowing that Bob's package is the cause. The only hint for Alice is the INCOHERENT pragma that signals danger, and you propose to take that away. Olaf

2 1

[ANN] zsh-haskell
by Marcin Szamotulski 16 Feb '20

16 Feb '20

Dear fellow Haskellers, I am pleased to announce a `zsh` completion for `cabal`, `ghc` and `ghc-pkg`. https://github.com/coot/zsh-haskell Cheers, Marcin Szamotulski

1 0

Taking over maintainership of cautious-file (or does anyone know of an alternative?)
by Brent Yorgey 15 Feb '20

15 Feb '20

The cautious-file package http://hackage.haskell.org/package/cautious-file has not been updated by the maintainer, Robin Green, since 2013 (though there have been a few Hackage trustee updates since then). The linked source repository was hosted on patch-tag.com and no longer exists. I tried contacting the maintainer on January 25 but have not heard back. I hereby announce my intention to take over as maintainer of the package. (As a side note, as far as I know my diagrams-haddock package is the only thing on Hackage that depends on it.) Alternatively, if anyone knows of a different, actively maintained package that provides similar functionality, I'd love to hear about it! -Brent

3 4

ghc runtime linker problem on i386
by Olaf Klinke 14 Feb '20

14 Feb '20

Dear Cafe, I'm experiencing strange behaviour on an old i386 machine when interpreting Haskell code on the fly: The same code runs from GHCi and fails as compiled executable. It might be a GHC runtime linker problem but I'm not sure. I successfully built haskintex and IHaskell with stack 2.1.3 on that machine. Both programs are supposed to interpret Haskell code at runtime: IHaskell uses the GHC API while haskintex uses hint, which itself is a wrapper for the GHC API. Therefore I suspect the problem lies in the usage of the GHC API itself. Both programs fail at runtime with the same error: $LIBDIR/ghc-prim-0.5.3/HSghc-prim-0.5.3.o: unknown symbol `_GLOBAL_OFFSET_TABLE_` When adding -dynamic to the ghc-options field in the package cabal file, the error goes away. Minimal code to reproduce is below. The i386 machine has no system ghc, no cabal, no ghcup and I wiped the $HOME/.stack directory before running "stack build". On x86-64 the error does not occur regardless of the -dynamic flag. Should I file a bug report or is this expected behaviour? If this is a bug, who should I file the bug against? Olaf {-- put this as app/Main.hs in a new stack project --} module Main where import Language.Haskell.Interpreter -- hint main :: IO () main = putStrLn =<< hintstuff hintstuff :: IO String hintstuff = fmap (either show show).runInterpreter $ do setImports ["Prelude"] interpret "1+2" (as :: Int)

1 0

Interpreting synchronized streams (pre-IO monad Haskell)
by Jiri Jakes 13 Feb '20

13 Feb '20

Heλλo! Before introduction of IO monad, first versions of Haskell used synchronised streams [1]: main :: [Response] -> [Request] where Response and Request were ADTs containing all possible actions and responses: data Request = ReadFile Name | ... | AppendChan Name String | ... data Response = Success | Str String | Bn Bin | Failure ... I wanted to write an interpreter of this representation using a simplified version: import System.Environment (getArgs) data Response = Success | StrList [String] data Request = GetArgs | PutStr String eval :: Request -> IO Response eval GetArgs = StrList <$> getArgs eval (PutStr s) = putStrLn s >> return Success main' :: [Response] -> [Request] main' ~(StrList args : _) = [ GetArgs, PutStr (show args) ] main :: IO () main = ??? I can imagine how interpreting main' could work, thanks to laziness. However, when actually trying to implement it, I get lost. I cannot figure out how could I read requests (result of calling main') before having something to pass to main'. Having a look at ancient version of GHC [2] didn't help either. Is it actually possible without some low-level tricks? Perhaps using mutually recursive functions? Or by converting to continuations somehow? Thank you! Jiri [1] http://haskell.org/definition/haskell-report-1.0.ps.gz [2] https://downloads.haskell.org/~ghc/0.29/ghc-0.29-src.tar.gz

2 1

Re: [Haskell-cafe] [ANN] Documentation for base-4.13.0.0 & GHC 8.8.1
by 石井大海 13 Feb '20

13 Feb '20

Oops, sorry I've sent the question only to Fumi mistakingly. Here I re-send to Cafe. Sorry! > 2020/02/13 13:28、石井大海 <konn.jinro(a)gmail.com>のメール: > > Hi, > > What's the difference with documentations already distributed with GHC Users' Guide? > > * https://downloads.haskell.org/~ghc/8.8.2/docs/html/ <https://downloads.haskell.org/~ghc/8.8.2/docs/html/> > * https://downloads.haskell.org/~ghc/8.8.2/docs/html/libraries/ghc-8.8.2/inde… <https://downloads.haskell.org/~ghc/8.8.2/docs/html/libraries/ghc-8.8.2/inde…> > * https://downloads.haskell.org/~ghc/8.8.2/docs/html/libraries/index.html <https://downloads.haskell.org/~ghc/8.8.2/docs/html/libraries/index.html> > > Are they hooglable? > >> 2020/02/13 13:20、Fumiaki Kinoshita <fumiexcel(a)gmail.com <mailto:fumiexcel@gmail.com>>のメール: >> >> It seems unlikely that they will be uploaded to Hackage anytime soon, so I decided to host them on my server. >> >> http://docs.hask.moe/base-4.13.0.0/index.html <http://docs.hask.moe/base-4.13.0.0/index.html> >> >> GHC 8.8.1: http://docs.hask.moe/ghc-8.8.1/index.html <http://docs.hask.moe/ghc-8.8.1/index.html> >> >> Hope this helps >> _______________________________________________ >> Haskell-Cafe mailing list >> To (un)subscribe, modify options or view archives go to: >> http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe <http://mail.haskell.org/cgi-bin/mailman/listinfo/haskell-cafe> >> Only members subscribed via the mailman list are allowed to post. >

2 1

Re: [Haskell-cafe] [Job] Cloudseal seeks Haskell Software Engineers
by tomas gallegos 13 Feb '20

13 Feb '20

Hello there, My name is Tomas Gallegos and I specialize in functional programming using Haskell. I am very interested in this Haskell job position. It would be great if we could talk to discuss this position further and maybe schedule an interview. Thank you for your time and consideration, I look forward to hearing from you.(Attached to this email is my resume). Regards, Tomas Gallegos

6 7

[ANN] Documentation for base-4.13.0.0 & GHC 8.8.1
by Fumiaki Kinoshita 13 Feb '20

13 Feb '20

It seems unlikely that they will be uploaded to Hackage anytime soon, so I decided to host them on my server. http://docs.hask.moe/base-4.13.0.0/index.html GHC 8.8.1: http://docs.hask.moe/ghc-8.8.1/index.html Hope this helps

1 0

[ANN] BNFC-meta 0.6.1 release -- embedded Happy parsers
by Artem Pelenitsyn 13 Feb '20

13 Feb '20

Hello! BNFC-meta 0.6.1 has been released. The library [1,2] allows you to define simple parsers inside your source files using BNF-like formalism by the way of Template Haskell. A couple of small example applications are hosted here [3]. Details are described in the Haskell '11 paper [4] (preprint [5]). Compared with the previous release, support for recent GHCs is added. Also a minor problem with spaces after closing parenthesis in pretty-printer is fixed courtesy GitHub user @mbuszka. [1]: http://hackage.haskell.org/package/BNFC-meta [2]: https://github.com/ulysses4ever/BNFC-meta [3]: https://github.com/ulysses4ever/BNFC-meta-examples [4]: https://dl.acm.org/doi/10.1145/2096148.2034689 [5]: http://www.cse.chalmers.se/~patrikj/papers/MetaDSL_preprint_20110325.pdf -- Cheers, Artem

1 0

Re: [Haskell-cafe] [Job] Cloudseal seeks Haskell Software Engineers
by tomas jose gallegos 12 Feb '20

12 Feb '20

Hello there, My name is Tomas Gallegos and I specialize in functional programming using Haskell. I am very interested in this Haskell job position. It would be great if we could talk to discuss this position further and maybe schedule an interview. Thank you for your time and consideration, I look forward to hearing from you.(Attached to this email is my resume). Regards, Tomas Gallegos Sent with [ProtonMail](https://protonmail.com) Secure Email.

1 0