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Today's Topics:
1. Re: cannot install system.filesystem (akash g)
2. Re: More type errors I'm having trouble with (Dan Stromberg)
----------------------------------------------------------------------
Message: 1
Date: Thu, 3 Dec 2015 17:34:37 +0530
From: akash g <akabe...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] cannot install system.filesystem
Message-ID:
<caliga_cpzsgnrjvgrfhemqspwwcvyf+ysuk2aj5s91asvcw...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
You are probably using GHC 7.10. With this, you will need any data type to
be an instance of applicative and functor for it to be an instance of
Monad. However, I don't see a version 1.0.0 for said package.
See the below link for more information. You might try your luck asking
the maintainer for a fix for this. Or you can copy this locally, make
those changes yourself and see how it goes.
https://ghc.haskell.org/trac/ghc/wiki/Migration/7.10
On Thu, Dec 3, 2015 at 5:24 PM, <galeo...@tiscali.it> wrote:
>
> Hello,
> what's wrong (see below)????
> Thank you in advance,
> Maurizio
>
> C:\Documents and Settings\xxx1>cabal install FileSystem
> Resolving dependencies...
> cabal: Could not resolve dependencies:
> trying: FileSystem-1.0.0 (user goal)
> next goal: bytestring (dependency of FileSystem-1.0.0)
> rejecting: bytestring-0.10.6.0/installed-3a6..., 0.10.6.0, 0.10.4.1,
> 0.10.4.0,
> 0.10.2.0, 0.10.0.2, 0.10.0.1, 0.10.0.0 (conflict: FileSystem =>
> bytestring==0.9.*)
> trying: bytestring-0.9.2.1
> trying: directory-1.2.2.0/installed-678... (dependency of FileSystem-1.0.0)
> next goal: Win32 (dependency of directory-1.2.2.0/installed-678...)
> rejecting: Win32-2.3.1.0/installed-071... (conflict: bytestring==0.9.2.1,
> Win32 => bytestring==0.10.6.0/installed-3a6...)
> rejecting: Win32-2.3.1.0, 2.3.0.2, 2.3.0.1, 2.3.0.0, 2.2.2.0, 2.2.1.0,
> 2.2.0.2, 2.2.0.1, 2.2.0.0, 2.1.0.0, 2.1 (conflict: directory =>
> Win32==2.3.1.0/installed-071...)
> Dependency tree exhaustively searched.
>
> C:\Documents and Settings\xxx1>cabal install FileSystem --allow-newer
> Resolving dependencies...
> Downloading FileSystem-1.0.0...
> Configuring FileSystem-1.0.0...
> Building FileSystem-1.0.0...
> Preprocessing library FileSystem-1.0.0...
> [1 of 9] Compiling System.FileSystem.Utils ( System\FileSystem\Utils.hs,
> dist\bu
> ild\System\FileSystem\Utils.o )
> [2 of 9] Compiling System.FileSystem.Types ( System\FileSystem\Types.hs,
> dist\bu
> ild\System\FileSystem\Types.o )
>
> System\FileSystem\Types.hs:123:82:
> No instance for (Applicative (FST m))
> arising from the 'deriving' clause of a data type declaration
> Possible fix:
> use a standalone 'deriving instance' declaration,
> so you can specify the instance context yourself
> When deriving the instance for (Monad (FST m))
>
> System\FileSystem\Types.hs:123:89:
> No instance for (Applicative (FST m))
> arising from the 'deriving' clause of a data type declaration
> Possible fix:
> use a standalone 'deriving instance' declaration,
> so you can specify the instance context yourself
> When deriving the instance for (MonadIO (FST m))
> Failed to install FileSystem-1.0.0
> cabal: Error: some packages failed to install:
> FileSystem-1.0.0 failed during the building phase. The exception was:
> ExitFailure 1
>
>
>
>
> Connetti gratis il mondo con la nuova indoona: hai la chat, le chiamate,
> le video chiamate e persino le chiamate di gruppo.
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Message: 2
Date: Thu, 3 Dec 2015 13:49:48 -0800
From: Dan Stromberg <strom...@gmail.com>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <beginners@haskell.org>
Subject: Re: [Haskell-beginners] More type errors I'm having trouble
with
Message-ID:
<caovkw55foh2qywtn+rp899xgp7hgwby1qjn0sw_qb1fkhv1...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thank you!
You're correct; I had been thinking of do notation as a "multistatement"
thing rather than as a monad thing.
On Wed, Dec 2, 2015 at 5:05 AM, David McBride <toa...@gmail.com> wrote:
> You seem to be having some problems understanding how Monads and do
> notation work.
>
> do_prefix_hash :: String -> (IO String, String)
> do_prefix_hash filename = do
> hash <- Md5s.prefix_md5 filename :: (IO String)
> (hash, filename)
>
> The above is ill typed. When you open with a do, from that point on the
> type will be Monad m => String -> m Something. But what you intended to
> return is a tuple, which is not an instance of monad. Don't use do in this
> case, just return a tuple.
>
> do_prefix_hash :: String -> (IO String, String)
> do_prefix_hash filename = (Md5s.prefix_md5 filename, filename)
>
> Just look closely at what the error is telling you. Is it expecting a
> type that you told it it returns but it is detecting that your code would
> return something else.
>
>
> On Tue, Dec 1, 2015 at 7:12 PM, Dan Stromberg <strom...@gmail.com> wrote:
>
>>
>> I'm continuing my now-and-then exploration of Haskell.
>>
>> I'm getting a new crop of type errors that I'm pulling my hair out over.
>>
>> The errors I'm getting are:
>>
>> $ make
>> below cmd output started 2015 Tue Dec 01 04:05:17 PM PST
>> # --make will go out and find what to build
>> ghc -Wall --make -o dph dph.hs Split0.hs
>> [1 of 3] Compiling Split0 ( Split0.hs, Split0.o )
>> [2 of 3] Compiling Md5s ( Md5s.hs, Md5s.o )
>> [3 of 3] Compiling Main ( dph.hs, dph.o )
>>
>> dph.hs:13:13:
>> Couldn't match type `IO' with `(,) (IO String)'
>> Expected type: (IO String, String)
>> Actual type: IO String
>> In a stmt of a 'do' block: hash <- prefix_md5 filename :: IO String
>> In the expression:
>> do { hash <- prefix_md5 filename :: IO String;
>> (hash, filename) }
>> In an equation for `do_prefix_hash':
>> do_prefix_hash filename
>> = do { hash <- prefix_md5 filename :: IO String;
>> (hash, filename) }
>>
>> dph.hs:14:6:
>> Couldn't match type `[Char]' with `IO String'
>> Expected type: IO String
>> Actual type: String
>> In the expression: hash
>> In a stmt of a 'do' block: (hash, filename)
>> In the expression:
>> do { hash <- prefix_md5 filename :: IO String;
>> (hash, filename) }
>>
>> dph.hs:24:23:
>> Couldn't match type `[]' with `IO'
>> Expected type: IO (IO String, String)
>> Actual type: [(IO String, String)]
>> In a stmt of a 'do' block:
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)]
>> In the expression:
>> do { buffer <- (hGetContents stdin) :: IO String;
>> let filenames = ...;
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)];
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)];
>> .... }
>> In an equation for `main':
>> main
>> = do { buffer <- (hGetContents stdin) :: IO String;
>> let filenames = ...;
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)];
>> .... }
>>
>> dph.hs:25:20:
>> Couldn't match type `[a0]' with `(String, String)'
>> Expected type: [(String, String)]
>> Actual type: [[a0]]
>> In the return type of a call of `sequence'
>> In a stmt of a 'do' block:
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)]
>> In the expression:
>> do { buffer <- (hGetContents stdin) :: IO String;
>> let filenames = ...;
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)];
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)];
>> .... }
>>
>> dph.hs:25:20:
>> Couldn't match type `[]' with `IO'
>> Expected type: IO (String, String)
>> Actual type: [(String, String)]
>> In a stmt of a 'do' block:
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)]
>> In the expression:
>> do { buffer <- (hGetContents stdin) :: IO String;
>> let filenames = ...;
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)];
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)];
>> .... }
>> In an equation for `main':
>> main
>> = do { buffer <- (hGetContents stdin) :: IO String;
>> let filenames = ...;
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)];
>> .... }
>>
>> dph.hs:25:29:
>> Couldn't match expected type `[[a0]]'
>> with actual type `(IO String, String)'
>> In the first argument of `sequence', namely `io_hash_tuples'
>> In a stmt of a 'do' block:
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)]
>> In the expression:
>> do { buffer <- (hGetContents stdin) :: IO String;
>> let filenames = ...;
>> io_hash_tuples <- map do_prefix_hash filenames ::
>> [(IO String, String)];
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)];
>> .... }
>>
>> dph.hs:26:39:
>> Couldn't match expected type `[(String, String)]'
>> with actual type `(String, String)'
>> In the second argument of `map', namely `hash_tuples'
>> In the expression: map tuple_to_string hash_tuples :: [String]
>> In an equation for `strings':
>> strings = map tuple_to_string hash_tuples :: [String]
>> make: *** [dph] Error 1
>> above cmd output done 2015 Tue Dec 01 04:05:18 PM PST
>>
>>
>> dph.hs looks like:
>> import Md5s
>> import Split0
>> import System.IO
>>
>> get_filenames :: String -> [String]
>> get_filenames buffer = do
>> -- Let's hope this doesn't give locale-related roundtrip problems.
>> Split0.split0 '\0' buffer :: [String]
>>
>> do_prefix_hash :: String -> (IO String, String)
>> do_prefix_hash filename = do
>> hash <- Md5s.prefix_md5 filename :: (IO String)
>> (hash, filename)
>>
>> tuple_to_string :: (String, String) -> String
>> tuple_to_string (first, second) = do
>> (show first) ++ " " ++ (show second)
>>
>> main :: IO ()
>> main = do
>> buffer <- (System.IO.hGetContents System.IO.stdin) :: IO String
>> let filenames = (get_filenames buffer) :: [String]
>> io_hash_tuples <- map do_prefix_hash filenames :: [(IO String,
>> String)]
>> hash_tuples <- sequence io_hash_tuples :: [(String, String)]
>> let strings = map tuple_to_string hash_tuples :: [String]
>> mapM_ putStrLn strings
>>
>>
>> And Md5s.hs looks like:
>> module Md5s where
>>
>> import qualified System.IO
>> import qualified Text.Printf
>> -- cabal install cryptohash
>> import qualified Crypto.Hash.MD5
>> import qualified Data.ByteString
>> import qualified Data.ByteString.Lazy
>>
>> --
>> http://stackoverflow.com/questions/10099921/efficiently-turn-a-bytestring-into-a-hex-representation
>> byte_string_to_hex :: Data.ByteString.ByteString -> String
>> byte_string_to_hex = concatMap (Text.Printf.printf "%02x") .
>> Data.ByteString.unpack
>>
>> prefix_md5 :: String -> IO String
>> prefix_md5 filename = do
>> let prefix_length = 1024
>> file <- System.IO.openBinaryFile filename System.IO.ReadMode :: IO
>> System.IO.Handle
>> data_read <- Data.ByteString.hGet file prefix_length :: IO
>> Data.ByteString.ByteString
>> _ <- System.IO.hClose file
>> let hasher = Crypto.Hash.MD5.init :: Crypto.Hash.MD5.Ctx
>> let hasher2 = Crypto.Hash.MD5.update hasher data_read ::
>> Crypto.Hash.MD5.Ctx
>> let binary_digest = Crypto.Hash.MD5.finalize hasher2 ::
>> Data.ByteString.ByteString
>> let hex_digest = byte_string_to_hex binary_digest :: String
>> return hex_digest :: IO String
>>
>> full_md5 :: String -> IO String
>> full_md5 filename = do
>> file <- System.IO.openBinaryFile filename System.IO.ReadMode :: IO
>> System.IO.Handle
>> data_read <- Data.ByteString.Lazy.hGetContents file :: IO
>> Data.ByteString.Lazy.ByteString
>> let binary_digest = Crypto.Hash.MD5.hashlazy data_read ::
>> Data.ByteString.ByteString
>> let hex_digest = byte_string_to_hex binary_digest :: String
>> -- Does this get closed for us later?
>> -- strace shows the file getting closed without our explicit close.
>> -- _ <- System.IO.hClose file
>> return hex_digest :: IO String
>>
>>
>> It might be easier to view these at
>> http://stromberg.dnsalias.org/svn/equivalence-classes/trunk/equivs3-haskell/
>> , so the line numbers are precise.
>>
>> What is the deal?
>>
>> Can anyone tell me what should be running through my head to fix this
>> kind of problem on my own in the future?
>>
>> Thanks!
>>
>> --
>> Dan Stromberg
>>
>> _______________________________________________
>> Beginners mailing list
>> Beginners@haskell.org
>> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
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> http://mail.haskell.org/cgi-bin/mailman/listinfo/beginners
>
>
--
Dan Stromberg
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