- Haskell-Cafe - Haskell.org

confusion about cabal-install install
by Alexander Solla 11 May '14

11 May '14

I'm trying to install cabal-install. I ran: $ cabal update && cabal install cabal-install After compiling, cabal reported: Installing executable(s) in /home/ajs/.cabal/bin Installed cabal-install-1.20.0.1 But now consider: $ cabal --version cabal-install version 1.16.0.2 using version 1.16.0 of the Cabal library $ which cabal /home/ajs/.cabal/bin/cabal $ /home/ajs/.cabal/bin/cabal --version cabal-install version 1.20.0.1 using version 1.20.0.0 of the Cabal library I am confused. My path is set to point to "$HOME/.cabal/bin/:$PATH"

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Re: [Haskell-cafe] loop problem
by Roelof Wobben 11 May '14

11 May '14

Stuart A. Kurtz schreef op 10-5-2014 18:02: > Dear Roelof, > > >> Thanks , it's working now like this : >> >> loop :: Int -> IO () >> loop n = do >> if n <= 100 >> then do >> putStrLn (show n ); >> putChar ' '; >> putStrLn (show (n * n )) ; >> loop (n + 1); >> else >> return () ; >> >> main :: IO () >> main = loop 1 >> >> But the outcome looks like this: >> >> 1 >> 1 >> 2 >> 4 > You're getting good advice, but this strikes me as extraordinarily unidiomatic Haskell -- it reads like a translated C program. Fixing it doesn't eliminate that sense. > > Why not this? > > main :: IO () > main = putStr . unlines . map (unwords . map show . (\n -> [n,n^2])) $ [1..100] > > Peace, > > Stu > > Like I said to another person . Im now following this course: https://www.fpcomplete.com/school/starting-with-haskell/basics-of-haskell But I get the feeling it's not a good one. Maybe find another tutorial/course where I can learn it the right way and do a lot of exercises so I can see if I understand things right. I learn the best by doing things and not only read about it. Roelof

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ANN: th-alpha
by Julian Arni 10 May '14

10 May '14

Hello Cafe, I just uploaded th-alpha to hackage [1]. This package primarily provides one function, 'areExpAEq', which compares expressions for alpha equivalence (equivalence modulo renaming of bound variables): >> areExpAEq [| \x -> x |] [| \y -> y |] True Pretty unambitious, but I found myself needing this when testing another library that uses Template Haskell, and it might be useful to others in that same situation. Cheers, Julian [1] https://hackage.haskell.org/package/th-alpha-0.1.0.2

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Re: [Haskell-cafe] loop problem
by Roelof Wobben 10 May '14

10 May '14

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Re: [Haskell-cafe] loop problem
by Roelof Wobben 10 May '14

10 May '14

Stuart A. Kurtz schreef op 10-5-2014 18:17: > Dear Roelof, > > I took a quick look at the course -- it wasn't immediately evident to me where you are in it. It looks pretty good, although more examples/exercise are always welcome. > > It occurred to me, though, if you're going to write it so it looks like C, you'd might as well take advantage of Text.Printf: > > import Control.Monad > import Text.Printf > > loop :: Int -> IO () > loop n = when (n <= 100) $ do > printf "%d %d\n" n (n^2) > loop $ n+1 > > main :: IO () > main = loop 1 > > Peace, > > Stu > > Sorry that I did not make that clear. So in your oponion this could be a good way to learn haskell very good. I get the feeling on your remarks that im not really to do things the haskell way and that is what im looking for. I have looked at the book http://learnyouahaskell.com/chapters but I miss there exercises What do you think about this one : http://www.umiacs.umd.edu/~hal/docs/daume02yaht.pdf Roelof

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intelij idea and haskell
by Roelof Wobben 10 May '14

10 May '14

Hello, Does anyone ever tried intelij idea with Haskell. I know there is a plugin. I know Intelij from the fact that I have tried to programm in Clojure and I like the enviroment. Roelof

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loop problem
by Roelof Wobben 10 May '14

10 May '14

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Bug in GHC (probably parser) regarding GADTs
by Brian Nguyen 10 May '14

10 May '14

The following does not work: data Foo a where {Foo :: (->) a (Foo a)} Someone please file a bug for me, I can't on my computer.

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Re: [Haskell-cafe] ANN: hsqml-0.3.0.0 supports Qt 5
by Robin KAY 10 May '14

10 May '14

Dear Andrew, On 09/05/14 16:42, Andrew Voron wrote: [snip] > I've tryed to compile sample project on windows - it compiles good, but > outputs: > Segmentation fault/access violation in generated code > when I'm trying to start executables. As described in the installation section on my web-site [1], this problem is most likely caused by an incompatibility between the MinGW tool-chains shipped with the Haskell Platform and with the Qt binaries. In fact, writing that in the docs was probably too coy, as the latest Haskell Platform and the latest official Qt SDK for Windows will not work together. In the past, this was not the case but the respective copies of MinGW/gcc must now be too far out of step with each other. A relatively simple fix I have found to work is to modify the GHC settings file to point to the version of gcc.exe inside the Qt SDK distribution rather than GHC's. Otherwise, you could build your own Qt binaries using GHC's MinGW but that is rather more involved. [1] http://www.gekkou.co.uk/software/hsqml/#installation Regards, -- Robin KAY

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Haddock issue tracker is now on GitHub.
by Mateusz Kowalczyk 10 May '14

10 May '14

Greetings, The Haddock issue tracker now lives at [1]. The reasoning is that a lot of people have a GitHub account already and signing up just for Trac is tedious. Hopefully this will also allow people to see more easily what's going on. This also removes the maintenance load from Haskell infrastructure: the Trac instance has been bitrotting quite a bit and recently even sending out e-mail about tickets stopped working. Old issues have been migrated over so the ticket numbers still correspond. Please file any new issues or make issue comments on GitHub. If you do not wish to use GitHub (which is fairly understandable) then please send me the report directly and I will create one for you. Thanks. [1]: https://github.com/haskell/haddock/issues?state=open -- Mateusz K.

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