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Today's Topics:
1. Re: very impure [global] counter (Thomas)
2. Re: another list comprehesion error (Roelof Wobben)
3. Re: another list comprehesion error (David Place)
4. Re: another list comprehesion error (David Place)
5. Haskell state monad example - type mismatch error (Rohit Garg)
6. Re: Haskell state monad example - type mismatch error
(Antoine Latter)
7. Re: Haskell state monad example - type mismatch error
(aditya siram)
8. Re: Haskell state monad example - type mismatch error
(Rohit Garg)
9. Re: another list comprehesion error (Roelof Wobben)
----------------------------------------------------------------------
Message: 1
Date: Fri, 22 Jul 2011 12:08:17 +0200
From: Thomas <[email protected]>
Subject: Re: [Haskell-beginners] very impure [global] counter
To: [email protected]
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
I may misunderstand the issue, but why not using:
System.IO.Temp.openTempFile
and then use the returned FilePath?
This should give unique names even for multiple runs of the controlling
program.
On 22.07.2011 11:46, David McBride wrote:
> This is what I'd do:
>
> {-# LANGUAGE NoMonomorphismRestriction #-}
> module Counter where
>
> import Control.Monad.State
>
> main = runStateT procedure (0 :: Integer)>> return ()
>
> incCounter = do
> n<- get
> modify (+1)
> return n
>
> execFile = do
> n<- incCounter
> liftIO $ putStrLn $ ("command --createfile=tempfile" ++ show n ++ ".tmp")
>
> procedure = do
> execFile
> execFile
> liftIO $ putStrLn "do something"
> execFile
>
> On Fri, Jul 22, 2011 at 3:10 AM, Davi Santos<[email protected]> wrote:
>> Hello all,
>> I have massive (parallel if possible) system calls to an external
>> non-deterministic program.
>> Each time it is executed, it creates a file depending on a command line
>> option 'opt' (input files path, for example).
>> How can I ensure the file name will be unique? maybe with a global counter?
>> My temporary solution have been to use a large random number:
>> -----------
>> mysteriousExecution :: String -> IO ()
>> mysteriousExecution opt = do
>> number<- rand
>> run $ "mysterious-command " ? opt ? " --create-file=" ? number
>> rand = do
>> a ? getStdRandom (randomR (1,999999999999999999999999999999999)) ? IO
>> Int
>> let r = take 20 $ randomRs ('a','z') (mkStdGen a) ? String
>> return r
>> ========
>> I'm trying to avoid additional parameters to 'mysteriousExecution'.
>> I tried a counter also (to replace rand), but I don't know how could I start
>> it inside 'mysteriousExecution'.
>> c ? IO Counter
>> c = do
>> r ? newIORef 0 -- start
>> return (do
>> modifyIORef r (+1)
>> readIORef r)
>> If somebody says everything is wrong, ok.
>> I understand. 18 years of imperative programming world can damage the brain.
>> Thanks
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 2
Date: Fri, 22 Jul 2011 10:37:30 +0000
From: Roelof Wobben <[email protected]>
Subject: Re: [Haskell-beginners] another list comprehesion error
To: <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Oke,
Thanks.
I was wondering one thing and I think at this moment too difficult for me,
But can you with a list comprehession read one list and alter another list.
For example:
You have a list of numbers
Now you would calculate the average value and put the outcome in another list.
Just wondering so you have to say it can or cannot be done.
Roelof
----------------------------------------
> Date: Fri, 22 Jul 2011 11:31:07 +0200
> From: [email protected]
> To: [email protected]
> Subject: Re: [Haskell-beginners] another list comprehesion error
>
> On 22.07.2011 08:46, Roelof Wobben wrote:
>
> >> Now try this instead:
> >> roelof' n = [x | x<- [1..n]]
> >> What do you get for "roelof' 4" ?
> > A error message that a instance of print is missing.
>
> Then you have a typo somewhere...
>
> >> Now you can try the last two with guards.
>
> > 2) cannot be done without guards and list comprehession generator [ 2,4
> > ..10] does not work
>
> Sure it can:
> [ 2*x-1 | x <- [1..5]]
> and even easier:
> [1,3..10]
> or, better still (but not only a list comprehension any more):
> take 5 [1, 3..]
>
> > 3) cannot be done withut guards and list comprehession because of the a<=b
>
> This, too, can be done:
> [ (b, a) | a <- [1..5], b <- [1..a]]
>
> Regards,
> Thomas
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
------------------------------
Message: 3
Date: Fri, 22 Jul 2011 10:27:29 -0400
From: David Place <[email protected]>
Subject: Re: [Haskell-beginners] another list comprehesion error
To: Roelof Wobben <[email protected]>
Cc: "<[email protected]>" <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Hi, Roelof.
When you are working to unders
_____________________
David F. Place
Owner, Panpipes Ho!, LLC
http://panpipesho.com
On Jul 22, 2011, at 6:37 AM, Roelof Wobben <[email protected]> wrote:
>
------------------------------
Message: 4
Date: Fri, 22 Jul 2011 10:32:03 -0400
From: David Place <[email protected]>
Subject: Re: [Haskell-beginners] another list comprehesion error
To: David Place <[email protected]>
Cc: "<[email protected]>" <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset=us-ascii
Whoops, sorry. I swiped the tiny send button on my iPhone.
Hi, Roelof.
When you are working to understand examples from "Programming in Haskell"
perhaps you can give page numbers so we can follow along.
Cheers,
David
____________________
David Place
Owner, Panpipes Ho! LLC
http://panpipesho.com
[email protected]
On Jul 22, 2011, at 10:27 AM, David Place wrote:
> Hi, Roelof.
>
> When you are working to unders
>
> _____________________
> David F. Place
> Owner, Panpipes Ho!, LLC
> http://panpipesho.com
>
> On Jul 22, 2011, at 6:37 AM, Roelof Wobben <[email protected]> wrote:
>
>>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
------------------------------
Message: 5
Date: Fri, 22 Jul 2011 20:20:23 +0530
From: Rohit Garg <[email protected]>
Subject: [Haskell-beginners] Haskell state monad example - type
mismatch error
To: [email protected]
Message-ID:
<cac1t7giu+t351fejy8v60udj2lok5sgvunujjbkewgzk2dy...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hi,
I am trying out a simple haskell state monad example. I think I have
understood the concept of monads, but I am getting stuck at using
State monad. As far as I understand, the code below should compile,
but it is throwing a type mismatch error in the argument to show. The
rest of the code, however, type checks all right.
If any one can point out what I am doing wrong, it would be really helpful.
Thanks and regards,
Rohit
===============================
import Control.Monad.State
import Data.Word
type LCGState = Word32
lcg :: LCGState -> (Integer, LCGState)
lcg s0 = (output, s1)
where s1 = 1103515245 * s0 + 12345
output = fromIntegral s1 * 2^16 `div` 2^32
seed :: LCGState
seed = 5
getRandom :: State LCGState Integer
getRandom = do
s0 <- get
let (x,s1) = lcg s0
put s1
return x
addThreeRandoms :: State LCGState Integer
addThreeRandoms = do
a <- getRandom
b <- getRandom
c <- getRandom
return (a+b+c)
main :: IO ()
main = putStrLn show(addThreeRandoms seed)
--
Rohit Garg
http://rpg-314.blogspot.com/
------------------------------
Message: 6
Date: Fri, 22 Jul 2011 09:59:29 -0500
From: Antoine Latter <[email protected]>
Subject: Re: [Haskell-beginners] Haskell state monad example - type
mismatch error
To: Rohit Garg <[email protected]>
Cc: [email protected]
Message-ID:
<cakjsnqhowov4rnaou_c8qo-ueykz7dxqsw7anfrxqokojcv...@mail.gmail.com>
Content-Type: text/plain; charset=UTF-8
On Fri, Jul 22, 2011 at 9:50 AM, Rohit Garg <[email protected]> wrote:
> Hi,
>
> I am trying out a simple haskell state monad example. I think I have
> understood the concept of monads, but I am getting stuck at using
> State monad. As far as I understand, the code below should compile,
> but it is throwing a type mismatch error in the argument to show. The
> rest of the code, however, type checks all right.
>
You need to include the function 'runState' or 'evalState' somewhere -
a value of type 'State x y' is not a function, so trying to apply it
to values as if it were a function is not going to work.
http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Monad-State-Lazy.html#v:runState
http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Monad-State-Lazy.html#v:evalState
Antoine
> If any one can point out what I am doing wrong, it would be really helpful.
>
> Thanks and regards,
> Rohit
>
> ===============================
> import Control.Monad.State
> import Data.Word
>
> type LCGState = Word32
>
> lcg :: LCGState -> (Integer, LCGState)
> lcg s0 = (output, s1)
> ? ?where s1 = 1103515245 * s0 + 12345
> ? ? ? ? ?output = fromIntegral s1 * 2^16 `div` 2^32
>
> seed :: LCGState
> seed = 5
>
> getRandom :: State LCGState Integer
> getRandom = do
> ? ?s0 <- get
> ? ?let (x,s1) = lcg s0
> ? ?put s1
> ? ?return x
>
> addThreeRandoms :: State LCGState Integer
> addThreeRandoms = do
> ? ?a <- getRandom
> ? ?b <- getRandom
> ? ?c <- getRandom
> ? ?return (a+b+c)
>
> main :: IO ()
> main = putStrLn show(addThreeRandoms seed)
>
> --
> Rohit Garg
>
> http://rpg-314.blogspot.com/
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
------------------------------
Message: 7
Date: Fri, 22 Jul 2011 10:05:15 -0500
From: aditya siram <[email protected]>
Subject: Re: [Haskell-beginners] Haskell state monad example - type
mismatch error
To: Antoine Latter <[email protected]>
Cc: [email protected]
Message-ID:
<cajrreygjedyuz8xtmmsvgewr_shtay59izhatyns9b6ckfw...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
Hi,
Your main function needs to be:
main :: IO ()
main = putStrLn $ show $ runState addThreeRandoms seed
=>(70496,695785320)
if you want to preserve the final state
or:
main' :: IO ()
main' = putStrLn $ show $ execState addThreeRandoms seed
=>695785320
if you don't.
-deech
On Fri, Jul 22, 2011 at 9:59 AM, Antoine Latter <[email protected]> wrote:
> On Fri, Jul 22, 2011 at 9:50 AM, Rohit Garg <[email protected]> wrote:
>> Hi,
>>
>> I am trying out a simple haskell state monad example. I think I have
>> understood the concept of monads, but I am getting stuck at using
>> State monad. As far as I understand, the code below should compile,
>> but it is throwing a type mismatch error in the argument to show. The
>> rest of the code, however, type checks all right.
>>
>
> You need to include the function 'runState' or 'evalState' somewhere -
> a value of type 'State x y' is not a function, so trying to apply it
> to values as if it were a function is not going to work.
>
> http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Monad-State-Lazy.html#v:runState
> http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Monad-State-Lazy.html#v:evalState
>
> Antoine
>
>> If any one can point out what I am doing wrong, it would be really helpful.
>>
>> Thanks and regards,
>> Rohit
>>
>> ===============================
>> import Control.Monad.State
>> import Data.Word
>>
>> type LCGState = Word32
>>
>> lcg :: LCGState -> (Integer, LCGState)
>> lcg s0 = (output, s1)
>> ? ?where s1 = 1103515245 * s0 + 12345
>> ? ? ? ? ?output = fromIntegral s1 * 2^16 `div` 2^32
>>
>> seed :: LCGState
>> seed = 5
>>
>> getRandom :: State LCGState Integer
>> getRandom = do
>> ? ?s0 <- get
>> ? ?let (x,s1) = lcg s0
>> ? ?put s1
>> ? ?return x
>>
>> addThreeRandoms :: State LCGState Integer
>> addThreeRandoms = do
>> ? ?a <- getRandom
>> ? ?b <- getRandom
>> ? ?c <- getRandom
>> ? ?return (a+b+c)
>>
>> main :: IO ()
>> main = putStrLn show(addThreeRandoms seed)
>>
>> --
>> Rohit Garg
>>
>> http://rpg-314.blogspot.com/
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
------------------------------
Message: 8
Date: Fri, 22 Jul 2011 20:59:07 +0530
From: Rohit Garg <[email protected]>
Subject: Re: [Haskell-beginners] Haskell state monad example - type
mismatch error
To: aditya siram <[email protected]>
Cc: [email protected]
Message-ID:
<cac1t7gjuokesbpu9o274ga4bthzupke1aq7f5nxr+4t5qje...@mail.gmail.com>
Content-Type: text/plain; charset=ISO-8859-1
On Fri, Jul 22, 2011 at 8:35 PM, aditya siram <[email protected]> wrote:
> Hi,
> Your main function needs to be:
> main :: IO ()
> main = putStrLn $ show $ runState addThreeRandoms seed
> =>(70496,695785320)
> if you want to preserve the final state
>
> or:
> main' :: IO ()
> main' = putStrLn $ show $ execState addThreeRandoms seed
> =>695785320
>
> if you don't.
Thanks. This cleared up the matter.
>
> -deech
>
>
> On Fri, Jul 22, 2011 at 9:59 AM, Antoine Latter <[email protected]> wrote:
>> On Fri, Jul 22, 2011 at 9:50 AM, Rohit Garg <[email protected]> wrote:
>>> Hi,
>>>
>>> I am trying out a simple haskell state monad example. I think I have
>>> understood the concept of monads, but I am getting stuck at using
>>> State monad. As far as I understand, the code below should compile,
>>> but it is throwing a type mismatch error in the argument to show. The
>>> rest of the code, however, type checks all right.
>>>
>>
>> You need to include the function 'runState' or 'evalState' somewhere -
>> a value of type 'State x y' is not a function, so trying to apply it
>> to values as if it were a function is not going to work.
>>
>> http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Monad-State-Lazy.html#v:runState
>> http://hackage.haskell.org/packages/archive/mtl/latest/doc/html/Control-Monad-State-Lazy.html#v:evalState
>>
>> Antoine
>>
>>> If any one can point out what I am doing wrong, it would be really helpful.
>>>
>>> Thanks and regards,
>>> Rohit
>>>
>>> ===============================
>>> import Control.Monad.State
>>> import Data.Word
>>>
>>> type LCGState = Word32
>>>
>>> lcg :: LCGState -> (Integer, LCGState)
>>> lcg s0 = (output, s1)
>>> ? ?where s1 = 1103515245 * s0 + 12345
>>> ? ? ? ? ?output = fromIntegral s1 * 2^16 `div` 2^32
>>>
>>> seed :: LCGState
>>> seed = 5
>>>
>>> getRandom :: State LCGState Integer
>>> getRandom = do
>>> ? ?s0 <- get
>>> ? ?let (x,s1) = lcg s0
>>> ? ?put s1
>>> ? ?return x
>>>
>>> addThreeRandoms :: State LCGState Integer
>>> addThreeRandoms = do
>>> ? ?a <- getRandom
>>> ? ?b <- getRandom
>>> ? ?c <- getRandom
>>> ? ?return (a+b+c)
>>>
>>> main :: IO ()
>>> main = putStrLn show(addThreeRandoms seed)
>>>
>>> --
>>> Rohit Garg
>>>
>>> http://rpg-314.blogspot.com/
>>>
>>> _______________________________________________
>>> Beginners mailing list
>>> [email protected]
>>> http://www.haskell.org/mailman/listinfo/beginners
>>>
>>
>> _______________________________________________
>> Beginners mailing list
>> [email protected]
>> http://www.haskell.org/mailman/listinfo/beginners
>>
>
--
Rohit Garg
http://rpg-314.blogspot.com/
------------------------------
Message: 9
Date: Fri, 22 Jul 2011 15:33:57 +0000
From: Roelof Wobben <[email protected]>
Subject: Re: [Haskell-beginners] another list comprehesion error
To: <[email protected]>
Message-ID: <[email protected]>
Content-Type: text/plain; charset="iso-8859-1"
Oke',
But they are not examples but exercises.
Roelof
----------------------------------------
> Subject: Re: [Haskell-beginners] another list comprehesion error
> From: [email protected]
> Date: Fri, 22 Jul 2011 10:32:03 -0400
> CC: [email protected]; [email protected]
> To: [email protected]
>
> Whoops, sorry. I swiped the tiny send button on my iPhone.
>
> Hi, Roelof.
>
> When you are working to understand examples from "Programming in Haskell"
> perhaps you can give page numbers so we can follow along.
>
> Cheers,
> David
>
> ____________________
> David Place
> Owner, Panpipes Ho! LLC
> http://panpipesho.com
> [email protected]
>
>
>
> On Jul 22, 2011, at 10:27 AM, David Place wrote:
>
> > Hi, Roelof.
> >
> > When you are working to unders
> >
> > _____________________
> > David F. Place
> > Owner, Panpipes Ho!, LLC
> > http://panpipesho.com
> >
> > On Jul 22, 2011, at 6:37 AM, Roelof Wobben <[email protected]> wrote:
> >
> >>
> >
> > _______________________________________________
> > Beginners mailing list
> > [email protected]
> > http://www.haskell.org/mailman/listinfo/beginners
>
------------------------------
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End of Beginners Digest, Vol 37, Issue 46
*****************************************
