- Beginners - Haskell.org

-no-pie
by Dennis Raddle 13 Jan '19

13 Jan '19

I'm on MacOS Sierra. I'm using stack, but I also sometimes use the system GHC for situations where stack is problematic (one of my applications spawns GHC as part of a work-loop cycle and it's faster to run the system GHC). My system GHC is 8.4.2. I just started getting an error on compilation with the system GC: clang: error unknown argument: -no-pie Does I just need to update the system GHC or is this a symptom of something deeper? D

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Overlapping instances via Nat-kind
by Dannyu NDos 02 Jan '19

02 Jan '19

Hi everyone. I'm not so skillful with GADTs and DataKinds, so I assume this mailing list is appropriate to post on. Basically, I wanted to do GADT like this (involving GHC.TypeNats): data Symmetric (n :: Nat) where S1 :: Symmetric 1 (:.) :: (KnownNat n, 2 <= n) => Cyclic n -> Symmetric (n-1) -> Symmetric n But I had some issues with this. The full question is here (on Stack Overflow): https://stackoverflow.com/q/54000646/4540658 Sincerely, Dannyu NDos

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fclabels-2.0.3.3 build hangs on ghc-8.6.3/cabal-2.4.1.0 under Windows 10
by Graham Gill 27 Dec '18

27 Dec '18

While trying to build the haskell-ide-engine project (https://github.com/haskell/haskell-ide-engine) on Windows 10, using my system global install of ghc-8.6.3, the process seems to hang while building fclabels-2.0.3.3. (I followed the project build instructions, using command > .\build-all.ps1 8.6.3 in the project root folder, which uses stack resolver lts-13.0 and ghc-8.6.3.) I get the same result (process never finishes) trying to build fclabels by itself: > stack install fclabels --stack-yaml .\stack-8.6.3.yaml in the haskell-ide-engine root folder. To simplify, I tried to build fclabels with cabal install (cabal-2.4.1.0) in my home folder (where there are no .cabal files present): > cabal -v -j1 v2-install fclabels Output is attached. The process hangs at compiling Data.Label.Base source to object file. Windows task manager shows ghc working merrily away (overnight, on my first attempt) without finishing. On the other hand, if I run > stack install fclabels --stack-yaml .\stack-8.4.4.yaml in the haskell-ide-engine root folder, which uses stack resolver lts-12.20 and ghc-8.4.4, fclabels-2.0.3.3 builds successfully. Because of the complexity of cabal and stack package management I don't know where to pin the blame, perhaps it's on my own system setup, hence don't know where/whether to file a bug report. Regards, Graham

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MonadThrow, MonadReader and shake
by PICCA Frederic-Emmanuel 19 Dec '18

19 Dec '18

Hello, I try to write this sort of code xdsme' :: SomeDataCollection -> Maybe Cell -> Maybe SpaceGroup -> GZiped -> [Path Abs File] -> ReaderT Beamline IO () xdsme' c@(SomeDataCollection SCollect SHdf5 _) cell sg z is = do -- xdsme compute the output path by himself. cwd' <- toProcessDataPath c rdir <- resultsPrefixFile xdsMePrefix c dir <- resultsPrefixDir ("xdsme_" ++ xdsMePrefix) c dir' <- resultsPrefixFile "" c xmlPath <- parseRelFile $ toFilePath dir' ++ "_xdsme.xml" xml <- parseAbsFile $ toFilePath cwd' </> toFilePath dir </> toFilePath xmlPath uploadedPath <- parseRelFile $ toFilePath dir' ++ "_xdsme.uploaded" uploaded <- parseAbsFile $ toFilePath cwd' </> toFilePath dir </> toFilePath uploadedPath let shakeFiles' = toFilePath cwd' </> toFilePath dir </> ".shake/" let images = getImages c z liftIO $ shake shakeOptions{ shakeFiles=shakeFiles' , shakeReport=["/tmp/shake.html"] , shakeVerbosity=Diagnostic} $ do want [toFilePath uploaded] -- execute xdsme and deal with input dependencies toFilePath xml %> \_out -> do need (map toFilePath is) processXdsMe cwd' cell sg rdir images toFilePath uploaded %> \_out -> do need [toFilePath xml] container <- liftIO . fromFile . toFilePath $ xml -- post processing let attachment = _autoProcProgramAttachment . _autoProcProgramContainer $ container attachment' <- toRuchePath attachment <- HERE PROBLEM _ <- copyAttachment' attachment attachment' let container' = (autoProcProgramContainer . autoProcProgramAttachment .~ attachment') container -- replace attachement -- upload into ISPYB liftIO $ storeAutoProcIntoISPyB c NoAnomalous container' cmd_ ("touch" :: String) (toFilePath uploaded) where toRuchePath :: (MonadReader Beamline m, MonadThrow m) => [AutoProcProgramAttachment WithPrefix] -> m [AutoProcProgramAttachment ISPyB] toRuchePath = mapM go where go :: (MonadReader Beamline m, MonadThrow m) => AutoProcProgramAttachment WithPrefix -> m (AutoProcProgramAttachment ISPyB) go a = do (d, _) <- toPath a b <- ask newd <- mkText255 . pack . toRuchePath' b . fromAbsDir $ d return a {filePath = newd} but when I try to compile this I get this error. How can I teach ghc how to solve this issue ? thanks for your help Frederic src/XdsMe.hs:211:22-43: error: • Could not deduce (MonadThrow Action) arising from a use of ‘toRuchePath’ from the context: t ~ 'Collect bound by a pattern with constructor: SCollect :: SCollectType 'Collect, in an equation for ‘xdsme'’ at src/XdsMe.hs:180:30-37 or from: f ~ 'ISPyB.DataCollection.Hdf5 bound by a pattern with constructor: SHdf5 :: SCollectSourceFormat 'ISPyB.DataCollection.Hdf5, in an equation for ‘xdsme'’ at src/XdsMe.hs:180:39-43 • In a stmt of a 'do' block: attachment' <- toRuchePath attachment In the expression: do { need [toFilePath xml]; container <- liftIO . fromFile . toFilePath $ xml; let attachment = _autoProcProgramAttachment . _autoProcProgramContainer $ container; attachment' <- toRuchePath attachment; .... } In the second argument of ‘(%>)’, namely ‘\ _out -> do { need [...]; container <- liftIO . fromFile . toFilePath $ xml; .... }’

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Regex
by mike h 12 Dec '18

12 Dec '18

Hi, Which package is the most popular and/or easy to used for dealing with regular expressions? My regex is quite simple and I just need to get 2 or 3 capture groups from the result. Many thanks Mike

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monad and variable result
by Damien Mattei 10 Dec '18

10 Dec '18

have some code that works but want to put it in a simple function without sucess: getBD :: Connection -> String -> Float getBD conn name = noBDfp where qry_head = "select `N° BD` from sidonie.Coordonnées where Nom = ?" :: Query bd_rows = do local_bd_rows <- query conn qry_head (Only (name::String)) return local_bd_rows i want the variable local_bd_rows accessible in the 'where' clause how can i do that? note the goal is to do the same thing of my main function that works : main :: IO () --main :: Int main = do conn <- connect defaultConnectInfo { connectHost = "moita", connectUser = "mattei", connectPassword = "******", connectDatabase = "sidonie" } -- we get all the Double Stars that have angular distance superior to a threshold of 1 second = 0.000278 degree rows <- query_ conn "SELECT Nom,distance FROM AngularDistance WHERE distance > 0.000278" forM_ rows $ \(name,distance) -> putStrLn $ Text.unpack name ++ " " ++ show (distance :: Double) -- we will get the Durchmusterung Number BD from Sidonie and WDS and compare them for a given name -- Warning: there could be multiple result in WDS for a given entry name (due to components) -- first we get the N°BD from sidonie let name = "A 20" -- let qry = "select `N° BD` from Coordonnées where Nom = " ++ name let qry_head = "select `N° BD` from sidonie.Coordonnées where Nom = ?" :: Query -- bd_rows <- query_ conn "select `N° BD` from sidonie.Coordonnées where Nom = 'A 20'" bd_rows <- query conn qry_head (Only (name::String)) putStrLn $ show bd_rows putStrLn $ show name let resLst = Prelude.map fromOnly bd_rows let noBDtxt = fromOnly (Prelude.head bd_rows) :: Text -- let noBD2 = _ (Prelude.head bd_rows) putStrLn $ show resLst putStrLn $ show noBDtxt forM_ bd_rows $ \(Only a) -> putStrLn $ Text.unpack a let noBDstr = Text.unpack noBDtxt :: String let noBDfp = read $ noBDstr :: Float putStr "noBDfp =" (putStrLn (show noBDfp)) close conn print "Exit." for now i have errors in the function: Prelude> :load UpdateSidonie [1 of 1] Compiling Main ( UpdateSidonie.hs, interpreted ) UpdateSidonie.hs:47:28: error: • Ambiguous type variable ‘r0’ arising from a use of ‘query’ prevents the constraint ‘(QueryResults r0)’ from being solved. Relevant bindings include bd_rows :: IO [r0] (bound at UpdateSidonie.hs:46:9) Probable fix: use a type annotation to specify what ‘r0’ should be. These potential instances exist: instance Result a => QueryResults (Only a) -- Defined in ‘Database.MySQL.Simple.QueryResults’ instance (Result a, Result b) => QueryResults (a, b) -- Defined in ‘Database.MySQL.Simple.QueryResults’ instance (Result a, Result b, Result c) => QueryResults (a, b, c) -- Defined in ‘Database.MySQL.Simple.QueryResults’ ...plus 21 others (use -fprint-potential-instances to see them all) • In a stmt of a 'do' block: local_bd_rows <- query conn qry_head (Only (name :: String)) In the expression: do local_bd_rows <- query conn qry_head (Only (name :: String)) return local_bd_rows In an equation for ‘bd_rows’: bd_rows = do local_bd_rows <- query conn qry_head (Only (name :: String)) return local_bd_rows | 47 | local_bd_rows <- query conn qry_head (Only (name::String)) | ^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^^ Failed, no modules loaded. -- Damien.Mattei(a)unice.fr, Damien.Mattei(a)oca.eu, UNS / OCA / CNRS

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database, list result, extraction and conversion
by Damien Mattei 07 Dec '18

07 Dec '18

again un haskell beginner question ;-) ... i have this: [Only {fromOnly = "-04.3982"}] as result of a database query, i understand it's a list and i can get the first element: *Main> Data.List.head [Only {fromOnly = "-04.3982"}] Only {fromOnly = "-04.3982"} *Main> let s = Data.List.head [Only {fromOnly = "-04.3982"}] *Main> s Only {fromOnly = "-04.3982"} *Main> show s "Only {fromOnly = \"-04.3982\"}" but how can i get the String "-04.3982" ? and after converting it to a Float -- Damien.Mattei(a)unice.fr, Damien.Mattei(a)oca.eu, UNS / OCA / CNRS

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database error simply by using a sting in a variable
by Damien Mattei 05 Dec '18

05 Dec '18

why i'm getting this error? code: let name = "'A 20'" let qry = "select `N° BD` from Coordonnées where Nom = " ++ name putStrLn qry bd_rows <- query_ conn qry putStrLn $ show bd_rows putStrLn $ show name forM_ bd_rows $ \(Only a) -> putStrLn $ Text.unpack a error: *Main> :load UpdateSidonie [1 of 1] Compiling Main ( UpdateSidonie.hs, interpreted ) UpdateSidonie.hs:74:28: error: • Couldn't match expected type ‘Query’ with actual type ‘[Char]’ • In the second argument of ‘query_’, namely ‘qry’ In a stmt of a 'do' block: bd_rows <- query_ conn qry In the expression: do conn <- connect defaultConnectInfo {connectHost = "moita", connectUser = "mattei", connectPassword = "sidonie2", connectDatabase = "sidonie"} rows <- query_ conn "SELECT Nom,distance FROM AngularDistance WHERE distance > 0.000278" forM_ rows $ \ (name, distance) -> putStrLn $ unpack name ++ " " ++ show (distance :: Double) let name = "'A 20'" .... | 74 | bd_rows <- query_ conn qry | ^^^ Failed, no modules loaded. -- Damien.Mattei(a)unice.fr, Damien.Mattei(a)oca.eu, UNS / OCA / CNRS

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Database simple-mysql
by Damien Mattei 05 Dec '18

05 Dec '18

why does this works: let name = "'A 20'" bd_rows <- query_ conn "select `N° BD` from sidonie.Coordonnées where Nom = 'A 20'" putStrLn $ show bd_rows putStrLn $ show name i got: [Only {fromOnly = "-04.3982"}] "'A 20'" -04.3982 but not with this: bd_rows <- query conn "select `N° BD` from sidonie.Coordonnées where Nom = ?" (Only (name::String)) i got an empty result: [] ... ??? -- Damien.Mattei(a)unice.fr, Damien.Mattei(a)oca.eu, UNS / OCA / CNRS

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About Installing Sqlite3, HDBC and convertible
by Eyüp Kaan AKAY 05 Dec '18

05 Dec '18

Hi. I want to use sqlite3. When I work to install it, I got this error: hdbc-sqlite3-master$ ghc --make -o setup Setup.lhs hdbc-sqlite3-master$ ghc --make -o setup Setup.hs [1 of 1] Compiling Main ( Setup.hs, Setup.o ) Linking setup ... hdbc-sqlite3-master$ ./setup configure Configuring HDBC-sqlite3-2.3.3.1... setup: At least the following dependencies are missing: HDBC >=2.3.0.0, utf8-string -any When I want to install HDBC, I got this error: HDBC-2.4.0.2$ ghc --make -o setup Setup.lhs HDBC-2.4.0.2$ ./setup configure Configuring HDBC-2.4.0.2... setup: At least the following dependencies are missing: convertible >=1.1.0.0, utf8-string -any Then I install convertible and I got any errors then first I work to install HDBC but I got the same error. So what can I do else?

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