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Today's Topics:
1. Re: Haskell network sample (yang.zhao)
2. Instance declaration needs more info? (Dimitri DeFigueiredo)
3. Re: Instance declaration needs more info? (Bob Ippolito)
----------------------------------------------------------------------
Message: 1
Date: Wed, 21 May 2014 16:17:04 +0800
From: "yang.zhao" <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Haskell network sample
Message-ID:
<CAKXgZ3akenbAGFm+qKHVdp4hGnc0t8U+qv=zevrs1jsfrmv...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Thank you very much, Bob and Sylvain.
i test hGetLine instead of hGetContents.
2014-05-21 16:07 GMT+08:00 Sylvain Henry <[email protected]>:
> hGetContents puts the handle in semi-closed state and reads until there is
> nothing left to read. Hence you have a deadlock. Use hGetLine in "cli".
>
> Sylvain
>
>
> 2014-05-21 9:15 GMT+02:00 yang.zhao <[email protected]>:
>
> omg, i test it on Windows, it's ok now. GHC is 7.6.3.
>> i really don't konw why this happen..
>>
>> but there is another question on Windows
>>
>>
>> main = withSocketsDo $ do
>> s <- listenOn $ PortNumber $ fromIntegral port
>> putStrLn "Listening..."
>> (h, _, _) <- accept s
>> putStrLn "After accept"
>> sline <- hGetLine h
>> putStrLn $ "get line from handle"++sline
>> hPutStrLn h "xxxx...."
>> putStrLn "send first done"
>>
>> --second recv
>> slinea <- hGetLine h
>> putStrLn $ "get line from handle"++slinea
>>
>> hPutStrLn h "yyyy....."
>> putStrLn "send second done"
>>
>> threadDelay 1000000
>> --
>> cli:
>>
>> main = withSocketsDo $ do
>> h <- connectTo "127.0.0.1" $ PortNumber $ fromIntegral port
>> putStrLn "After connect"
>> hPutStrLn h "xxx"
>> putStrLn "put first to handle done"
>>
>> bs <- hGetContents h
>> putStrLn "read from handle done "
>> putStrLn bs
>>
>> --second send
>> hPutStrLn h "yyy"
>> putStrLn "put second to handle done"
>> bfs <- hGetContents h
>>
>> putStrLn "read from handle done "
>> putStrLn bs
>>
>>
>> the second send and recv is blocking...
>> server's output:
>> Listening...
>> After accept
>> get line from handlexxx
>> send first done
>>
>> client's output:
>> After connect
>> put first to handle done
>> read from handle done
>> xxx....
>>
>>
>> ..... T_T
>>
>>
>>
>>
>> 2014-05-21 14:10 GMT+08:00 yang.zhao <[email protected]>:
>>
>> Here's my new code:
>>>
>>> $ cat serv.hs
>>>
>>> import Control.Concurrent
>>> import System.IO
>>> import Network
>>>
>>> port :: Int
>>> port = 1234
>>>
>>> main :: IO ()
>>> main = withSocketsDo $ do
>>> s <- listenOn $ PortNumber $ fromIntegral port
>>> putStrLn "Listening..."
>>>
>>> (h, _, _) <- accept s
>>> putStrLn "After accept"
>>> sline <- hGetLine h
>>> putStrLn "get line from handle"
>>>
>>> hPutStrLn h sline
>>> putStrLn $ "send "++sline
>>> threadDelay 1000000
>>>
>>> hClose h
>>> sClose s
>>>
>>> --------
>>> $ cat clie.hs
>>>
>>> import System.IO
>>> import Network
>>>
>>> port :: Int
>>> port = 1234
>>>
>>> main :: IO ()
>>> main = withSocketsDo $ do
>>> h <- connectTo "127.0.0.1" $ PortNumber $ fromIntegral port
>>> putStrLn "After connect"
>>> hPutStrLn h "hello"
>>> putStrLn "put hello to handle done"
>>> bs <- hGetContents h
>>> putStrLn "read from handle done"
>>> putStrLn bs
>>> hClose h
>>>
>>>
>>> ===
>>> one terminal, run ./serv, then run ./clie in another terminal. Output is
>>> :
>>>
>>> $ ./serv
>>> Listening...
>>> After accept
>>>
>>> $ ./clie
>>> After connect
>>> put hello to handle done
>>> read from handle done
>>>
>>>
>>> it seems that client has read from then handle, but donesn't read
>>> anything, then block.
>>> and server donesn't receive anything, still wait for something...
>>>
>>> ghc version is 7.4.1, because of this?..
>>>
>>>
>>> 2014-05-21 13:57 GMT+08:00 Bob Ippolito <[email protected]>:
>>>
>>> Not sure why you're having issues, I just tried it on GHC 7.6.3 on
>>>> Fedora 20 and it worked fine there as well (both with runhaskell or
>>>> compiled with -O).
>>>>
>>>> I might start adding putStrLn statements to the code to see where it's
>>>> unexpectedly blocking, or perhaps use 127.0.0.1 instead of "localhost" in
>>>> case the issue is a DNS misconfiguration.
>>>>
>>>>
>>>>
>>>> On Tue, May 20, 2014 at 10:51 PM, yang.zhao <[email protected]> wrote:
>>>>
>>>>> thanks for your replay.
>>>>> i run the two program in two different teriminal for sure.
>>>>>
>>>>> it works for you?
>>>>> but why can't run well on my computer.
>>>>>
>>>>> make me creazy....
>>>>>
>>>>>
>>>>> 2014-05-21 13:47 GMT+08:00 Bob Ippolito <[email protected]>:
>>>>>
>>>>> How precisely are you trying to run the client? Are you typing it in
>>>>>> to the same terminal? If so, then the client is never actually started,
>>>>>> because when you type ./cli the input is going to ./serv and not the
>>>>>> shell.
>>>>>> Try running the client in a separate terminal.
>>>>>>
>>>>>> It works for me here on Mac OS X 10.9.2 with GHC 7.8.2.
>>>>>>
>>>>>>
>>>>>> On Tue, May 20, 2014 at 10:42 PM, yang.zhao <[email protected]>wrote:
>>>>>>
>>>>>>> hi guys,
>>>>>>> I'm newbie, just begin to learn Haskell.
>>>>>>> now i write a very simple server and client .
>>>>>>>
>>>>>>> Server:
>>>>>>> import Control.Concurrent
>>>>>>> import System.IO
>>>>>>> import Network
>>>>>>>
>>>>>>> port :: Int
>>>>>>> port = 1234
>>>>>>>
>>>>>>> main :: IO ()
>>>>>>> main = withSocketsDo $ do
>>>>>>> s <- listenOn $ PortNumber $ fromIntegral port
>>>>>>> (h, _, _) <- accept s
>>>>>>>
>>>>>>> sline <- hGetLine h
>>>>>>> hPutStrLn h sline
>>>>>>> putStrLn $ "send "++sline
>>>>>>> threadDelay 1000000
>>>>>>>
>>>>>>> hClose h
>>>>>>> sClose s
>>>>>>>
>>>>>>> Client :
>>>>>>> import System.IO
>>>>>>> import Network
>>>>>>>
>>>>>>> port :: Int
>>>>>>> port = 1234
>>>>>>>
>>>>>>> main :: IO ()
>>>>>>> main = withSocketsDo $ do
>>>>>>> h <- connectTo "localhost" $ PortNumber $ fromIntegral port
>>>>>>> hPutStrLn h "hello"
>>>>>>> bs <- hGetContents h
>>>>>>> putStrLn bs
>>>>>>> hClose h
>>>>>>>
>>>>>>>
>>>>>>> And, it doesn't work now . I run ./serv , then run ./cli , they will
>>>>>>> block all the time.
>>>>>>> but, when i run ./serv, and telnet localhost 1234 in another
>>>>>>> terminal, it works fine.
>>>>>>> so i don't know what's the wrong with my code.
>>>>>>> anybody can tell me about my problem?
>>>>>>>
>>>>>>> os is Debian 7, haskell-platform 2012.2.0.0
>>>>>>>
>>>>>>> thanks a lot!!!
>>>>>>> --
>>>>>>> K.I.S.S.
>>>>>>>
>>>>>>> _______________________________________________
>>>>>>> Beginners mailing list
>>>>>>> [email protected]
>>>>>>> http://www.haskell.org/mailman/listinfo/beginners
>>>>>>>
>>>>>>>
>>>>>>
>>>>>> _______________________________________________
>>>>>> Beginners mailing list
>>>>>> [email protected]
>>>>>> http://www.haskell.org/mailman/listinfo/beginners
>>>>>>
>>>>>>
>>>>>
>>>>>
>>>>> --
>>>>> K.I.S.S.
>>>>>
>>>>> _______________________________________________
>>>>> Beginners mailing list
>>>>> [email protected]
>>>>> http://www.haskell.org/mailman/listinfo/beginners
>>>>>
>>>>>
>>>>
>>>> _______________________________________________
>>>> Beginners mailing list
>>>> [email protected]
>>>> http://www.haskell.org/mailman/listinfo/beginners
>>>>
>>>>
>>>
>>>
>>> --
>>> K.I.S.S.
>>>
>>
>>
>>
>> --
>> K.I.S.S.
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
>
--
K.I.S.S.
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Message: 2
Date: Wed, 21 May 2014 03:18:59 -0600
From: Dimitri DeFigueiredo <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] Instance declaration needs more info?
Message-ID: <[email protected]>
Content-Type: text/plain; charset=ISO-8859-1; format=flowed
Hi All,
I'm trying to write a simplified dimensional library where where
quantities in meters, seconds and meters/second can all co-exist
adjusting their respective units when multiplied and/or divided.
Also, meter+meter is allowed, but meter+second should cause the type
checker to complain.
This is a bit like a *much* simplified version of the Units library.
However, I am having trouble understanding why my instance declaration
below appears to be under specified. Here's the code:
------------
module Dimensional where
import qualified Prelude
-- A Group allows you to add and subtract (but not multiply or divide)
class Group a where
(+) :: a -> a -> a
(-) :: a -> a -> a
x - y = x + negate y
negate :: a -> a
negate x = fromInteger 0 - x
fromInteger :: Prelude.Integer -> a
class Unit a where
(*) :: (Unit a, Unit b, Unit c) => a -> b -> c
(/) :: (Unit a, Unit b, Unit c) => a -> b -> c
toDouble :: a -> Prelude.Double
instance Unit Prelude.Double where
(*) x y = (Prelude.*) x (toDouble y) -- <----- Error here
(/) x y = (Prelude./) x (toDouble y)
toDouble x = x
------------
GHC complains as follows:
Could not deduce (c ~ Prelude.Double)
from the context (Unit Prelude.Double, Unit b, Unit c)
bound by the type signature for
* :: (Unit Prelude.Double, Unit b, Unit c) =>
Prelude.Double -> b -> c
at /code/haskell/dimensional.hs:25:5-43
`c' is a rigid type variable bound by
the type signature for
* :: (Unit Prelude.Double, Unit b, Unit c) =>
Prelude.Double -> b -> c
at /code/haskell/dimensional.hs:25:5
In the first argument of `(Prelude.*)', namely `x'
In the expression: (Prelude.*) x (toDouble y)
In an equation for `*': * x y = (Prelude.*) x (toDouble y)
Any pointers would be much appreciated!
Thanks,
Dimitri
------------------------------
Message: 3
Date: Wed, 21 May 2014 02:28:41 -0700
From: Bob Ippolito <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] Instance declaration needs more info?
Message-ID:
<cacwmpm9mz5pcmcmjdc7umcnw8ql4elkvbact4p5yn+dnwww...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
The trouble is that your specification says that Unit c is the return type
(the caller can choose any Unit instance), but this implementation can only
evaluate to a Prelude.Double. One way to solve this is to add a fromDouble
:: Double -> Unit a and wrap the expression with that in order to satisfy
Unit c.
On Wednesday, May 21, 2014, Dimitri DeFigueiredo <[email protected]>
wrote:
> Hi All,
>
> I'm trying to write a simplified dimensional library where where
> quantities in meters, seconds and meters/second can all co-exist adjusting
> their respective units when multiplied and/or divided.
>
> Also, meter+meter is allowed, but meter+second should cause the type
> checker to complain.
>
> This is a bit like a *much* simplified version of the Units library.
> However, I am having trouble understanding why my instance declaration
> below appears to be under specified. Here's the code:
>
> ------------
> module Dimensional where
> import qualified Prelude
>
> -- A Group allows you to add and subtract (but not multiply or divide)
> class Group a where
>
> (+) :: a -> a -> a
>
> (-) :: a -> a -> a
> x - y = x + negate y
>
> negate :: a -> a
> negate x = fromInteger 0 - x
>
> fromInteger :: Prelude.Integer -> a
>
> class Unit a where
>
> (*) :: (Unit a, Unit b, Unit c) => a -> b -> c
> (/) :: (Unit a, Unit b, Unit c) => a -> b -> c
> toDouble :: a -> Prelude.Double
>
> instance Unit Prelude.Double where
>
> (*) x y = (Prelude.*) x (toDouble y) -- <----- Error here
> (/) x y = (Prelude./) x (toDouble y)
> toDouble x = x
>
> ------------
> GHC complains as follows:
>
> Could not deduce (c ~ Prelude.Double)
> from the context (Unit Prelude.Double, Unit b, Unit c)
> bound by the type signature for
> * :: (Unit Prelude.Double, Unit b, Unit c) =>
> Prelude.Double -> b -> c
> at /code/haskell/dimensional.hs:25:5-43
> `c' is a rigid type variable bound by
> the type signature for
> * :: (Unit Prelude.Double, Unit b, Unit c) =>
> Prelude.Double -> b -> c
> at /code/haskell/dimensional.hs:25:5
> In the first argument of `(Prelude.*)', namely `x'
> In the expression: (Prelude.*) x (toDouble y)
> In an equation for `*': * x y = (Prelude.*) x (toDouble y)
>
> Any pointers would be much appreciated!
>
> Thanks,
>
> Dimitri
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
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