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Today's Topics:
1. Directory statistics (Alexander.Vladislav.Popov )
2. Re: Please, help me for myFirstCode (Henk-Jan van Tuyl)
3. Re: Please, help me for myFirstCode (David McBride)
4. Re: Please, help me for myFirstCode (Brent Yorgey)
----------------------------------------------------------------------
Message: 1
Date: Tue, 26 Oct 2010 13:14:17 +0600
From: "Alexander.Vladislav.Popov "
<alexander.vladislav.po...@gmail.com>
Subject: [Haskell-beginners] Directory statistics
To: beginners@haskell.org
Message-ID:
<aanlktin_aphblq1mccd+frav5z8dpmao_h2am8jm5...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
Hi, haskellers.
Iâve written a program to assess directory utilization in the selected
path. It displays on the console a list indicating directory size and
path. The list is sorted by descending size. I need some criticism and
some models I could follow to write a more concise and expressive
program.
Thanks in advance.
Alexander.
> {-# LANGUAGE ScopedTypeVariables #-}
> module Main (main) where
> import Control.Exception (SomeException, finally, bracket, handle)
> import Control.Monad
> import Data.List
> import System.Directory
> import System.Environment
> import System.IO
> import Text.Printf
> main :: IO ()
> main = do
> args <- getArgs
> if null args
> then
> putStr "Displays directory utilization in the selected
> path.\nUsage: dirstat <path>\n"
> else
> mapM_ ds3 args
It safely returns a file size. If an error occurs during file opening,
it will return 0.
> filesize :: FilePath -> IO Integer
> filesize path = (withFile path ReadMode hFileSize) `catch` const (return 0)
Get size of a directory.
> ds :: FilePath -> IO Integer
> ds path = do
> contents <- getDirectoryContents path `catch` const (return [])
> let visibles = getVisible contents
> let path' = clrSlash path
> a <- (liftM sum) $ sequence $ map (\p -> filesize (path' `mkpath` p))
> visibles -- size of a current dir
> (liftM ((+a) . sum)) $ mapM (\p -> ds (path' `mkpath` p)) visibles --
> current + children
Returns a list of pairs: (file size, path)
> ds2 :: FilePath -> IO [(Integer, FilePath)]
> ds2 path = do
> contents <- getDirectoryContents path
> let visibles = getVisible contents
> let path' = clrSlash path
> let paths = map (\p -> path' `mkpath` p) visibles
> let pairs = map (\p -> (ds p, p)) paths
> a <- sequenceFst pairs
> return $ (reverse . sort . filter (\e -> fst e > 0)) a
Compare it to the function *sequence :: (Monad m) => [m a] -> m [a]*
> sequenceFst :: (Monad m) => [(m t, t1)] -> m [(t, t1)]
> {-# INLINE sequenceFst #-}
> sequenceFst ms = foldr k (return []) ms
> where
> k (ms, p) m' = do { s <- ms; xs <- m'; return ((s,p):xs) }
Driver
> ds3 :: FilePath -> IO ()
> ds3 path = do
> s <- ds2 path
> prn s
> where
> prn [] = return ()
> prn (s:ss) = (putStr . showDir) s >> prn ss
Auxiliary
> skipDots = (`notElem` [".", ".."])
> getVisible = filter skipDots
> mkpath p1 p2 = p1 ++ "/" ++ p2
> clrSlash = reverse . dropWhile (\c -> c =='/' || c == '\\') . reverse
Displays information about a directory.
> showDir :: (Integer, String) -> String
> showDir (s,p) = printVolume s 3 ++ "\t" ++ show p ++ "\n"
*Main> shred "1234567890"
["123","456","789","0"]
> shred [] = []
> shred ss = (take 3 ss) : (shred (drop 3 ss))
*Main> prettyNum "1234567890"
"1 234 567 890"
> prettyNum = concat . intersperse " " . (map reverse) . reverse . shred .
> reverse
*Main> units (1024*1024*1024)
[1073741824,1048576,1024,1,0]
> units :: Integer -> [Integer]
> units 0 = [0]
> units x = x : units' x
> where
> units' 0 = []
> units' x = y : units' y
> where
> y = round (fromIntegral x / 1024)
Just SI prefixes
> prefix = ["B", "K", "M", "G", "T", "P", "E", "Z", "Y"]
*Main> tagged (1024*1024*1024)
[("1 073 741 824","B"),("1 048 576","K"),("1 024","M"),("1","G"),("0","T")]
> tagged x = (map (prettyNum . show) $ units x) `zip` prefix
*Main> printVolume (1024*1024*1024) 5
1 024 M
> printVolume x width = printf "%*s %s" width (fst one) (snd one)
> where
> one = head $ dropWhile (\p -> length (fst p) > width) $ tagged x
------------------------------
Message: 2
Date: Tue, 26 Oct 2010 15:34:13 +0200
From: "Henk-Jan van Tuyl" <hjgt...@chello.nl>
Subject: Re: [Haskell-beginners] Please, help me for myFirstCode
To: beginners@haskell.org, "Sok H. Chang" <shae...@gmail.com>
Message-ID: <op.vk6qnbj2pz0...@zen5.arnhem.chello.nl>
Content-Type: text/plain; charset=iso-8859-15; format=flowed;
delsp=yes
On Tue, 26 Oct 2010 08:36:58 +0200, Sok H. Chang <shae...@gmail.com> wrote:
-----------------------------------------------------------------------------------------------------------------------
> import System
> import System.Random
>
> main = do myHeader <- readFile "C:\\Documents and Settings\\myHeader.txt"
> putStrLn $ myExtractSentence myHeader
> myExtractSentence file = ary !! ranNoInt
> where
> ranNoInt =<< ranNo -- *mark
> ranNo = randomRIO (0, n-1)
> n = length ary
> ary = lines file
> ----------------------------------------------------------------------------------------------------------------------
> There are two questions.
>
> 1) I've got following error message.
> Haskell>ghc --make Test01.hs -o Test
> [1 of 1] Compiling Main ( Test01.hs, Test01.o )
>
> Test01.hs:10:9: parse error (possibly incorrect indentation)
>
> How can fix it?
The lay-out is wrong: putStrLn should be in the same column as the
"myHeader" above it; avoid tabs to prevent unexpected lay-out problems.
The lay-out could be like this:
-----------------------------------------------------------------------------------------------------------------------
main =
do
myHeader <- readFile "C:\\Documents and Settings\\myHeader.txt"
putStrLn $ myExtractSentence myHeader
-----------------------------------------------------------------------------------------------------------------------
>
> 2) Is it OK at "*mark" line?
>
Note that ranNoInt is a value inside the IO monad, you cannot use directly
as an index.
Regards,
Henk-Jan van Tuyl
--
http://Van.Tuyl.eu/
http://members.chello.nl/hjgtuyl/tourdemonad.html
--
------------------------------
Message: 3
Date: Tue, 26 Oct 2010 09:45:43 -0400
From: David McBride <dmcbr...@neondsl.com>
Subject: Re: [Haskell-beginners] Please, help me for myFirstCode
To: "Sok H. Chang" <shae...@gmail.com>
Cc: beginners@haskell.org
Message-ID:
<aanlkti=bnclbdy7gdy75+pyrbwgjmref5evholayt...@mail.gmail.com>
Content-Type: text/plain; charset="iso-8859-1"
2) No.
1) That is your syntax error. You should have "ranNoInt = <something>".
The =<< operator is meant for the definition of the function.
Try this:
import System
import System.Random
main = readFile "C:\\Documents and Settings\\myHeader.txt" >>=
myExtractSentence >>= putStrLn
myExtractSentence file = do
ranNoInt <- ranNo
return $ ary !! ranNoInt
where
ranNo = randomRIO (0, n-1)
n = length ary
ary = lines file
On Tue, Oct 26, 2010 at 2:36 AM, Sok H. Chang <shae...@gmail.com> wrote:
> Hello, everyone.
>
> I need help for my first code.
> I write this code for extracting one sentence from text file.
>
> The code is
>
> -----------------------------------------------------------------------------------------------------------------------
> import System
> import System.Random
>
> main = do myHeader <- readFile "C:\\Documents and Settings\\myHeader.txt"
> putStrLn $ myExtractSentence myHeader
> myExtractSentence file = ary !! ranNoInt
> where
> ranNoInt =<< ranNo -- *mark
> ranNo = randomRIO (0, n-1)
> n = length ary
> ary = lines file
>
> ----------------------------------------------------------------------------------------------------------------------
> There are two questions.
>
> 1) I've got following error message.
> Haskell>ghc --make Test01.hs -o Test
> [1 of 1] Compiling Main ( Test01.hs, Test01.o )
>
> Test01.hs:10:9: parse error (possibly incorrect indentation)
>
> How can fix it?
>
> 2) Is it OK at "*mark" line?
>
> Thank you.
>
> S. CHANG
>
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
>
>
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------------------------------
Message: 4
Date: Tue, 26 Oct 2010 10:16:06 -0400
From: Brent Yorgey <byor...@seas.upenn.edu>
Subject: Re: [Haskell-beginners] Please, help me for myFirstCode
To: beginners@haskell.org
Message-ID: <20101026141606.ga5...@seas.upenn.edu>
Content-Type: text/plain; charset=us-ascii
Just a meta-observation: although such a program might be easy in
other languages, a program involving file I/O and random number
generation is probably not a very good choice for one's first Haskell
program! Is there a particular book or tutorial you are following
along with?
-Brent
On Tue, Oct 26, 2010 at 03:36:58PM +0900, Sok H. Chang wrote:
> Hello, everyone.
>
> I need help for my first code.
> I write this code for extracting one sentence from text file.
>
> The code is
> -----------------------------------------------------------------------------------------------------------------------
> import System
> import System.Random
>
> main = do myHeader <- readFile "C:\\Documents and Settings\\myHeader.txt"
> putStrLn $ myExtractSentence myHeader
> myExtractSentence file = ary !! ranNoInt
> where
> ranNoInt =<< ranNo -- *mark
> ranNo = randomRIO (0, n-1)
> n = length ary
> ary = lines file
> ----------------------------------------------------------------------------------------------------------------------
> There are two questions.
>
> 1) I've got following error message.
> Haskell>ghc --make Test01.hs -o Test
> [1 of 1] Compiling Main ( Test01.hs, Test01.o )
>
> Test01.hs:10:9: parse error (possibly incorrect indentation)
>
> How can fix it?
>
> 2) Is it OK at "*mark" line?
>
> Thank you.
>
> S. CHANG
> _______________________________________________
> Beginners mailing list
> Beginners@haskell.org
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
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