December 2018 - Haskell-Cafe

Taking over maintainership of syb
by Sergey Vinokurov 25 Dec '18

25 Dec '18

I'd like to become maintainer of the syb package (http://hackage.haskell.org/package/syb) The current maintainer, José Pedro Magalhães, would like to step down and is looking for anyone interested in picking up the package (https://github.com/dreixel/syb/pull/19) Best regards, Sergey

2 1

trace output statements
by Damien Mattei 25 Dec '18

25 Dec '18

i have this function: -- this function will return th N°BD from Sidonie for a given name -- note: names have been standardized between Sidonie and WDS getBD :: Connection -> String -> IO Float getBD conn name = trace "Entering getBD" noBDfp where qry_head = "select `N° BD` from Coordonnées where Nom = ?" :: Query bd_rows :: IO [Only Text] bd_rows = query conn qry_head (Only (name::String)) -- noBDtxt :: [Text] -- noBDtxt = fromOnly (Prelude.head bd_rows) -- noBDtxt :: IO [Text] -- lg = fmap Prelude.length bd_rows -- lg2 = fmap show lg noBDtxt :: IO Text -- noBDtxt = trace "lg " (fmap (fromOnly . Prelude.head) bd_rows) noBDtxt = trace "assigning noBDtxt" (fmap (fromOnly . Prelude.head) bd_rows) -- noBDstr :: String -- noBDstr = Text.unpack noBDtxt noBDstr :: IO String noBDstr = trace "assigning noBDstr" (fmap Text.unpack noBDtxt) -- noBDfp = read $ noBDstr :: Float noBDfp :: IO Float noBDfp = fmap read noBDstr call by : let lstBD = Prelude.map (\elem -> getBD conn (Text.unpack (fst elem))) rows it works ok, in fact at some point it fails due to NULL sql value not again handle correctly , i have inserted trace statement that output variable, i understand it's not really good becaus it breaks the purity of haskell function, perheaps for this reason i have strange behavior of output: ... Entering getBD assigning noBDstr assigning noBDtxt Entering getBD assigning noBDstr assigning noBDtxt Entering getBD assigning noBDstr assigning noBDtxt *** Exception: UnexpectedNull {errSQLType = "VarString", errHaskellType = "Text", errFieldName = "N\194\176 BD", errMessage = "unexpected null in table Coordonn\195\169es of database sidonie"} *Main> you will notice noBDstr seems to be assigned before noBDtxt, but in the code i have the statements in this order: noBDtxt = trace "assigning noBDtxt" (fmap (fromOnly . Prelude.head) bd_rows) noBDstr :: IO String noBDstr = trace "assigning noBDstr" (fmap Text.unpack noBDtxt) i just want to understand wht's happening, this is not critical for code as it works... any idea? Damien

4 10

Re: [Haskell-cafe] Places to write and publish projects that 'explain ideas'
by Doug McIlroy 25 Dec '18

25 Dec '18

The project (or an appropriate-sized coherent piece thereof) seems like a good fit for the "programming pearls" department in the Journal of Functional Programming Doug McIlroy

1 0

Re: [Haskell-cafe] Places to write and publish projects that "explain ideas"?
by Siddharth Bhat 25 Dec '18

25 Dec '18

Regarding (1), as far as I'm aware, the requirements are flexible, but the general requirement is "published a paper at a good venue, either journal or conference". This implementation was a hobby project of mine, but I was hoping to be able to justify spending more time on it by finding a venue to publish it at. As for (2), it's mostly expository. The techniques that I am interesting in showing off have no known "simple" implementations as far as I'm aware -- scalar evolution, polyhedral compilation, some kinds of inter-procedural analyses, SSA, etc. do not have simple implementations. Indeed, the goal is to show how to write *optmising* compilers. Most compilers books teach one how to write *a compiler, *while there's a second course usually on compiler optimisation. I don't know of readable, clean implementations of, say, the SSA construction algorithm, or the scalar evolution analysis. Regarding nanopass: I think it makes a lot of sense as a philosophy as a way to architect compilers. However, there are a lot of nice haskell-isms to write compilers which are scattered throughout the literature, as far as I can tell: Hoopl, trees that grow, much of Matt might's work on abstracting abstract interpreters, Scrap-your-boilerplate style techniques, equality saturation, etc. which are all fantastic, but I've never seen them under the same umbrella. So that's a sketch of the general story I want to tell :) Thanks. ~Siddharth On Tue, Dec 25, 2018 at 7:30 PM Richard O'Keefe <raoknz(a)gmail.com> wrote: > > Question 1: what does your department require? The first person to > consult > is your supervisor. Helping students figure out where to publish is > definitely > part of a supervisor's job (speaking as a former supervisor of PhD > students). > > Question 2: what is the TOPIC of your publication? Since you are merely > (!) > demonstrating known techniques on a toy language, does it really count as > work on compilers? Is it software engineering? Is it computer science > education? Is the aim to develop something more maintainable? What is the > quality metric by which your work should be judged? > > Observation: if you haven't already read the "Nanopass" paper, > https://www.cs.indiana.edu/~dyb/pubs/nano-jfp.pdf , > you should do so now. http://nanopass.org/ is the associated web site. > There is also a mailing list, > https://groups.google.com/forum/#!forum/nanopass-framework > I think your aims are sufficiently close to theirs for you to have > interesting things to say to each other, despite you using Haskell and > them having used Scheme. > > >

1 0

Places to write and publish projects that "explain ideas"?
by Siddharth Bhat 25 Dec '18

25 Dec '18

Hello all, I have somewhat of an unorthodox problem. I've been writing on and off, a series on implementing compilers "beautifully" in haskell, called tiny-optimising-compiler <http://github.com/bollu/tiny-optimising-compiler>. They're literate haskell files, with the aim of explaining the really elegant ideas that exist in compilers literature - data flow analysis, abstract interpretation, SSA, continuations, scalar evolution, and some more slightly out-there / research-y things, like polyhedral compilation, equality saturation. However, I'm also a research student at my university, and am expected to publish before I graduate. I was looking for possible places to publish a project such as this, whose selling point would be "explains things elegantly, and possibly rewords standard things to nice looking haskell". Are there places where one could conceivably publish about such a project? If not, I forsee myself not being able to finish this project for a while longer, and that would make me sad. Thanks, and a merry christmas to all, ~Siddharth

4 4

Happy Haskell Programming for GHC 8.x
by Kazu Yamamoto 25 Dec '18

25 Dec '18

Hello Cafe, I'm happy to announce that Happy Haskell Programming (HHP) version 0.0.0 has been released: http://hackage.haskell.org/package/hhp In short, HHP is a fork from ghc-mod 4.1.6 and re-written for all GHC 8.x. Emacs front end is included. For more information, please read: https://github.com/kazu-yamamoto/hhp Merry Christmas and Happy Haskell Programming on Emacs with GHC 8.x! --Kazu

1 0

Reminder Dutch FP-Day 2019
by Bas Lijnse 24 Dec '18

24 Dec '18

Hi Everybody, Just a quick reminder. You can still register for the "FP Dag" 2019 on January 11 in Breda. The program and additional details are available at https://wiki.clean.cs.ru.nl/NL-FP_dag_2019 Registration closes on January 4. Participation is free, but registration is mandatory. To register simply reply to this e-mail with your name, affiliation (optional) and whether you intend to join us for dinner afterwards. Happy Holidays! Bas and Jan Martin

1 0

Re: [Haskell-cafe] Upload new version of indexed-extras or let me take over
by Yuji Yamamoto 24 Dec '18

24 Dec '18

Confirmed! Thanks! 2018年12月24日(月) 16:04 Alexis Williams <alexis(a)typedr.at>: > It's done. > > Alexis Williams > Sent from Polymail > <https://polymail.io/?utm_source=polymail&utm_medium=referral&utm_campaign=s…> > > On Sun, Dec 23rd, 2018 at 11:1 PM, Yuji Yamamoto < > whosekiteneverfly(a)gmail.com> wrote: > >> Thank you Reiner, and Alexis. >> >> But I'm afraid the new version doesn't look uploaded yet... >> http://hackage.haskell.org/package/indexed-extras >> If you're okay, I'd like you to add me to the GitHub Project and the >> maintainer on Hackage. >> Here're my accounts: >> >> http://hackage.haskell.org/user/igrep >> https://github.com/igrep/ >> >> 2018年12月20日(木) 6:49 Reiner Pope <reiner.pope(a)gmail.com>: >> >> (haskell-cafe to bcc) >> >> Hi Yuji, thanks for the ping and sorry for the delay. >> >> Alexis (cc'd) took over ownership of indexed and indexed-extras at the >> beginning of this year, but apparently her permissions to upload packages >> to Hackage got reset by a Hackage reset. I've now fixed that, so she can >> reupload now (she was generally much more prompt than me). >> >> I'll upload a new version tonight. >> >> Not required, but if you like I'm also happy to add you on the GitHub >> project and the Hackage packages if you'd like to give me your details. >> >> Reiner >> >> On Sat, Dec 15, 2018 at 1:42 AM Yuji Yamamoto < >> whosekiteneverfly(a)gmail.com> wrote: >> >> Hello, this is a reminder of the message I sent (only to Reiner) about >> three weeks ago. >> >> I'm developing some libraries in Haskell with your package indexed-extras >> <http://hackage.haskell.org/package/indexed-extras>. >> I found the package can't be built with the latest bifunctor package due >> to its version constraint. >> I sent a pull request <https://github.com/reinerp/indexed-extras/pull/8> >> to fix the problem and it has already been merged. >> Can you release the new version on Hackage? >> It's now the biggest obstacle developing my libraries depending on it. >> >> If you can't maintain the package anymore, I'm willing to take over. >> Thanks in advance. >> >> >> -- >> 山本悠滋 >> twitter: @igrep >> GitHub: https://github.com/igrep >> GitLab: https://gitlab.com/igrep >> Facebook: http://www.facebook.com/igrep >> >> >> >> -- >> 山本悠滋 >> twitter: @igrep >> GitHub: https://github.com/igrep >> GitLab: https://gitlab.com/igrep >> Facebook: http://www.facebook.com/igrep >> > > -- 山本悠滋 twitter: @igrep GitHub: https://github.com/igrep GitLab: https://gitlab.com/igrep Facebook: http://www.facebook.com/igrep

1 0

Upload new version of indexed-extras or let me take over
by Yuji Yamamoto 24 Dec '18

24 Dec '18

Hello, this is a reminder of the message I sent (only to Reiner) about three weeks ago. I'm developing some libraries in Haskell with your package indexed-extras <http://hackage.haskell.org/package/indexed-extras>. I found the package can't be built with the latest bifunctor package due to its version constraint. I sent a pull request <https://github.com/reinerp/indexed-extras/pull/8> to fix the problem and it has already been merged. Can you release the new version on Hackage? It's now the biggest obstacle developing my libraries depending on it. If you can't maintain the package anymore, I'm willing to take over. Thanks in advance. -- 山本悠滋 twitter: @igrep GitHub: https://github.com/igrep GitLab: https://gitlab.com/igrep Facebook: http://www.facebook.com/igrep

2 2

handling NULL value in database query with Maybe (or other ...)
by Damien Mattei 20 Dec '18

20 Dec '18

Hi, i have this query in SQL used by my Haskell code: let name = "A 20" -- return the list of N°BD from WDS for a given name let qry_head_WDS = "select DNUM from WDS where DISC = ?" :: Query putStrLn "before query WDS" bd_rows_WDS <- query conn qry_head_WDS (Only (name::String)) putStrLn "after query WDS" forM_ bd_rows_WDS $ \(Only a) -> putStrLn $ Text.unpack a works well if there is no NULL values in a database, but if NULL value for field N°BD i got this exception at runtime: before query WDS *** Exception: UnexpectedNull {errSQLType = "String", errHaskellType = "Text", errFieldName = "DNUM", errMessage = "unexpected null in table WDS of database sidonie"} *Main> i need some code ,perheaps uing Maybe to handle the NULL value in the field N°BD i think Haskell have special feature to program this , i read the article: https://lukeplant.me.uk/blog/posts/null-pointers-vs-none-vs-maybe/ but for now i have no concrete solution.... Regards, Damien -- Damien.Mattei(a)unice.fr, Damien.Mattei(a)oca.eu, UNS / OCA / CNRS

9 20