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Today's Topics:
1. How to structure your Haskell installation? (frode k)
2. Re: small expression evaluator (Henk-Jan van Tuyl)
3. Re: How to structure your Haskell installation? (Daniel Fischer)
4. Re: Recursion in monad (Chadda? Fouch?)
----------------------------------------------------------------------
Message: 1
Date: Tue, 22 Mar 2011 13:31:44 +0100
From: frode k <mailingl...@klevstul.com>
Subject: [Haskell-beginners] How to structure your Haskell
installation?
To: beginners@haskell.org
Message-ID:
<aanlktinfrp0t7zmmueegah4recf704+3civb3axk_...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
Hi.
I'm installing the Haskell Platform om my Linux box and need some tips on
how to structure the files on the OS. I need to install and use both GHC
6.12.3 and GHC 7.0.2. Hence I want to separate these installations. I've
setup two directories, one for each platform (related to the GHC):
# ls -d -1 $PWD/*.*
/usr/haskell/2010.2.0.0
/usr/haskell/2011.2.0.0
I've installed GHC-6.12.3 in "2010.2.0.0" and will install GHC-7.0.2 in
"2011.2.0.0".
My question is more related to where I should install the packages. When I
install a package using "runhaskell Setup ..." I assumed this to ONLY be
installed for the version of GHC I'm using when installing it. Am I right
about this?
Having $PATH pointing to GHC-6.12.3 I've done this when installing packages,
to add them to "2010.2.0.0":
- - - - - - -
cd /usr/src
wget
http://hackage.haskell.org/packages/archive/transformers/0.2.2.0/transformers-0.2.2.0.tar.gz
tar xzf transformers-0.2.2.0.tar.gz
cd transformers-0.2.2.0
runhaskell Setup configure --prefix=/usr/haskell/2010.2.0.0/
runhaskell Setup build
runhaskell Setup install
- - - - - - -
Later when I switch to GHC-7.0.2 I plan to install the packages into the
"2011.2.0.0" directory in stead.
Is this a good way to structure several Haskell installations on the same
system? Is there a "best practice" on how to structure the files? I want to
get this right from the start, to avoid having to go back and re-arrange
everything.
Regards,
Frode K
[k]
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Message: 2
Date: Tue, 22 Mar 2011 13:43:51 +0100
From: "Henk-Jan van Tuyl" <hjgt...@chello.nl>
Subject: Re: [Haskell-beginners] small expression evaluator
To: "Haskell Beginners List" <beginners@haskell.org>, "Petr Novotnik"
<pnovot...@googlemail.com>
Message-ID: <op.vsqwbd1lpz0...@zen5.arnhem.chello.nl>
Content-Type: text/plain; charset=iso-8859-15; format=flowed;
delsp=yes
On Tue, 22 Mar 2011 10:14:57 +0100, Henk-Jan van Tuyl <hjgt...@chello.nl>
wrote:
> On Tue, 22 Mar 2011 08:56:45 +0100, Petr Novotnik
> <pnovot...@googlemail.com> wrote:
>
>> data Person = Person {
>> personName :: String
>> , personAge :: Int
>> }
>> deriving (Show)
>>
>> exampleExpr :: Bool
>> exampleExpr = (VConst 99) .==. (VFunc personAge) $ Person "pete" 99
>>
>>
>> I was wondering, whether it'd be possible to enable defining expression
>> without the Value data constructors, i.e.
>>
>>
>> 99 .==. personAge $ Person "pete" 99
>
> You can write:
> 99 == personAge (Person "pete" 99)
>
Or you could write:
c .==. f = \x -> c == f x
test = 99 .==. personAge $ Person "pete" 99
The .==. operator is not symmetrical in this case, of course
Regards,
Henk-Jan van Tuyl
--
http://Van.Tuyl.eu/
http://members.chello.nl/hjgtuyl/tourdemonad.html
--
------------------------------
Message: 3
Date: Tue, 22 Mar 2011 14:05:57 +0100
From: Daniel Fischer <daniel.is.fisc...@googlemail.com>
Subject: Re: [Haskell-beginners] How to structure your Haskell
installation?
To: beginners@haskell.org
Message-ID: <201103221405.58024.daniel.is.fisc...@googlemail.com>
Content-Type: Text/Plain; charset="utf-8"
On Tuesday 22 March 2011 13:31:44, frode k wrote:
> Hi.
>
> I'm installing the Haskell Platform om my Linux box and need some tips
> on how to structure the files on the OS. I need to install and use both
> GHC 6.12.3 and GHC 7.0.2. Hence I want to separate these installations.
> I've setup two directories, one for each platform (related to the GHC):
>
> # ls -d -1 $PWD/*.*
> /usr/haskell/2010.2.0.0
> /usr/haskell/2011.2.0.0
>
> I've installed GHC-6.12.3 in "2010.2.0.0" and will install GHC-7.0.2 in
> "2011.2.0.0".
>
> My question is more related to where I should install the packages. When
> I install a package using "runhaskell Setup ..." I assumed this to ONLY
> be installed for the version of GHC I'm using when installing it. Am I
> right about this?
Yes. A package can only be installed for the compiler it was compiled with,
so to install it for multiple compilers you have to compile it repeatedly.
>
> Having $PATH pointing to GHC-6.12.3 I've done this when installing
> packages, to add them to "2010.2.0.0":
> - - - - - - -
> cd /usr/src
> wget
> http://hackage.haskell.org/packages/archive/transformers/0.2.2.0/transfo
> rmers-0.2.2.0.tar.gz tar xzf transformers-0.2.2.0.tar.gz
> cd transformers-0.2.2.0
> runhaskell Setup configure --prefix=/usr/haskell/2010.2.0.0/
> runhaskell Setup build
> runhaskell Setup install
> - - - - - - -
Install cabal-install, then
$ cabal install --with-compiler=/path/to/desired/ghc wanted-package
takes care of it automatically (after tweaking the settings in cabal's
config file). And it gets necessary Haskell dependencies automatically and
installs them, too.
>
> Later when I switch to GHC-7.0.2 I plan to install the packages into the
> "2011.2.0.0" directory in stead.
>
> Is this a good way to structure several Haskell installations on the
> same system? Is there a "best practice" on how to structure the files?
Don't know. I have everything under $HOME and let GHC and cabal figure out
how to organise packages. Works for me?.
> I want to get this right from the start, to avoid having to go back and
> re-arrange everything.
>
> Regards,
> Frode K
>
> [k]
------------------------------
Message: 4
Date: Tue, 22 Mar 2011 21:44:20 +0100
From: Chadda? Fouch? <chaddai.fou...@gmail.com>
Subject: Re: [Haskell-beginners] Recursion in monad
To: Adrian May <adrian.alexander....@gmail.com>
Cc: beginners@haskell.org
Message-ID:
<AANLkTi=uk9Z2Ky=gd+h_lzj6c8t2idgm+ep_kmbrj...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Tue, Mar 22, 2011 at 5:46 AM, Adrian May
<adrian.alexander....@gmail.com> wrote:
> OK I did this:
>
> import System.Random
>
> walk :: Int -> IO Int
> walk i = randomRIO (0,1) >>= \r -> return (i+r*2-1)
>
> say :: Int -> IO ()
> say i = putStrLn $ show i
>
> rep :: Int -> a -> (a -> IO a) -> (a -> IO ()) -> IO ()
> rep n i w s
> ????? | n<=0 = return ()
> ????? | otherwise = s i >> w i >>= \ii -> rep (n-1) ii w s
>
> main :: IO ()
> main = rep 10 50 walk say
>
> Is that the easiest way?
I don't know about "easiest", it's not bad though there are thing that
can be improved
> say i = putStrLn $ show i
This already exist and is called "print" (though its type is more
general than your signature).
> walk i = randomRIO (0,1) >>= \r -> return (i+r*2-1)
The >>= ... return is pretty ugly, it would rather be written as :
> walk i = fmap (\r -> i + r * 2 - 1) $ randomRIO (0,1)
> rep n i w s
Passing say and walk as parameter seems a bit overkill, I seriously
doubt that you'll ever need this exact structure again, and even then
passing a single action should be enough :
> rep n act i
> | n <= 0 = return ()
> | otherwise = act i >>= \x -> rep (n-1) act x
rep may also be written with standard monad operations :
> rep n act i = foldM (\x _ -> act x) i $ replicate (n-1) ()
Lastly it may be that the structure of the program itself,
particularly the use of randomRIO is suboptimal and a bit ugly, for a
throwaway program I would probably just use randomRs :
> main = do
> g <- newStdGen
> mapM_ print . tail . scanl (\i r -> i+r*2-1) 50 . take 10 $ randomRs (0,1) g
but for a more complex endeavour I would rather use a serious library
like mwc-random. (System.Random performances are awful)
--
Jeda?
------------------------------
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