Either example

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Re: Either example

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Re: GHCi (7.4.2) is working on ARM

Hi,

that’s no surprise:
“ARM support in the RTS linker (#5839) has been implemented.”
(http://www.haskell.org/ghc/docs/7.4.2/html/users_guide/release-7-4-2.html)

Greetings,
Joachim

Am Mittwoch, den 06.02.2013, 18:21 -0500 schrieb dude:
> I have also validated ghc 7.4.1 on the Ubuntu Precise distro booted on
> a BeagleXM.
> 
> There's no ghci included.
> 
> --dude
> 
> On 02/06/2013 08:15 AM, kenny lu wrote:
> 
> > I've got a Cubieboard a few weeks back. I started it off with Linaro
> > (Ubuntu) 12.06.  
> > Today I started to upgrade the OS to 12.11, which surprisingly came
> > with ghc 7.4.2.
> > 
> > 
> > And ghci magically works too.
> > 
> > 
> > Here are the links
> > 
> > 
> > http://www.cubieboard.org
> > 
> > 
> > sudo apt-get install update-manager-core
> > sudo apt-get update
> > sudo apt-get upgrade
> > sudo do-release-upgrade
> > 
> > 
> > Regards,
> > Kenny
> > 
> > 
> > 
> > 
> > 
> > 
> > _______________________________________________
> > Haskell-Cafe mailing list
> > Haskell-Cafe <at> haskell.org
> > http://www.haskell.org/mailman/listinfo/haskell-cafe
> 
> 
> -- 
> dude
> _______________________________________________
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--

-- 
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  nomeata <at> debian.org | ICQ# 74513189 | GPG-Keyid: 4743206C
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Sol vingt simple problem in various languages and systems

At 

https://gist.github.com/ckirkendall/2934374 

you find solutions in many languages to a simple programming problem: the evaluation of an expression in an environment.

I want to point your attention to the currently last three entries:

  - one using the UUAGC compiler to solve the problem in an aspect oriented way (entered by Jeroen Bransen (jbransen))
  - one using some Haskell features, libraries and extensions (entered by me (doaitse))
  - one using our attribute grammar combinators from the AspectAG package, which expresses the 
    various aspects in an attribute grammar style (entered by Marcos Viera (marcosomarviera))

In case you did not manage to avoid getting wound up in a discussion about programming languages you can find
ammunition here.

 Doaitse

arrow notation

I'd like to hear from anyone who's using arrow notation as supported by GHC,
because I'm planning a couple of changes to parts of it.

Re: Either example

Am 07.02.13 03:37, schrieb Jacob Thomas:
> Hello
> 
> I'm new to Haskell, and need help with figuring out the Either type...
> Any example to show how this works?

Maybe a program I wrote a while ago can help you get it.

https://github.com/ctbo/slitherlink

In Slitherlink.hs there is a function readProblem that can fail. It
returns either a String with an error message (Left) or the problem read
(Right).

[...]
readProblem :: String -> Either String Problem
readProblem s = do
            pl <- readProblemList s
            when (null pl) $ Left "Problem is empty."
            let columns = length $ head pl
            when (columns == 0) $ Left "Problem starts with an empty line."
            unless (all ((== columns) . length) pl) $ Left "Problem not
rectangular."
            let rows = length pl
            return $ listArray ((0, 0), (rows-1, columns-1)) $ concat pl
[...]

Or if you don't feel comfortable with using the Either monad, look at
the even simpler function readConstraint a few lines earlier in the same
file.

In the main solve.hs program this is used to output a meaningful error
message to the user if the input file is invalid:

[...]
  where work s n = case readProblem s of
             Left e -> putStrLn e
             Right p -> do
[...do something with the problem p...]

Hope this helps.

Harald

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Re: Either example

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Announce: LA Haskell User Group February Meeting

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Re: arrow notation

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Re: arrow notation

On Thu, Feb 07, 2013 at 02:49:40PM -0800, Conal Elliott wrote:
> Hi Ross,
> 
> I make some use of arrow notation, though sadly I often have to avoid it
> because my (pseudo-)"arrows" don't have arr. I'd love to see a variant that
> has restricted expressiveness in exchange for arr-freeness.

Are you familiar with Adam Megacz's "Generalized Arrows" work?
  http://www.cs.berkeley.edu/~megacz/garrows/

(I, too, would love to see Arrows-without-arr in Haskell)

> -- Conal

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vim: set ft=text :

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