May 2014 - Haskell-Cafe

Re: [Haskell-cafe] [Haskell] ANNOUNCE: jhc-0.8.1
by Henning Thielemann 11 May '14

11 May '14

Am 11.05.2014 22:20, schrieb John Meacham: > After a hiatus, jhc 0.8.1 is released. Could you clarify the current relation between jhc and ajhc. Are they independent from each other, or does ajhc still pull all features from jhc?

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Installation of package text failing installation on ghc 7.6.3
by Victor Miller 11 May '14

11 May '14

I just downloaded the latest Haskell platform (I realize that ghc might not be up-to-date in this) for my macbook. I installed it, which appeared to go without problems. However, when I tried to update the package text, I get the errors below. I suspect that the first error (not recognizing ' in a comment) cascades through the rest. How do you suggest fixing this (other than getting Bryan do drop the apostrophe :-))? Victor Configuring text-1.1.1.2... Building text-1.1.1.2... Preprocessing library text-1.1.1.2... Data/Text.hs:9:52: warning: missing terminating ' character [-Winvalid-pp-token] -- Copyright : (c) 2009, 2010, 2011, 2012 Bryan O'Sullivan, ^ Data/Text.hs:90:12: warning: missing terminating ' character [-Winvalid-pp-token] , foldl' ^ Data/Text.hs:92:13: warning: missing terminating ' character [-Winvalid-pp-token] , foldl1' ^ Data/Text.hs:151:14: warning: missing terminating ' character [-Winvalid-pp-token] --, lines' ^ Data/Text.hs:269:15: warning: missing terminating '"' character [-Winvalid-pp-token] -- character \"�\" (U+FFFD). Functions that perform this ^ Data/Text.hs:271:5: warning: missing terminating '"' character [-Winvalid-pp-token] -- \"Performs replacement on invalid scalar values\". ^ Data/Text.hs:304:12: warning: missing terminating '"' character [-Winvalid-pp-token] -- phrase \"Subject to fusion\". ^ Data/Text.hs:440:3: error: invalid preprocessing directive #-} ^ Data/Text.hs:477:4: error: invalid preprocessing directive #-} ^

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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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