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Today's Topics:
1. Re: garbage collected object (Norbert Melzer)
2. Re: garbage collected object (Ryan Trinkle)
3. Error while trying to install ByteString Package
(Abhinav Kalawatia)
4. help with IO guards (Miro Karpis)
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Message: 1
Date: Wed, 14 Jan 2015 13:12:11 +0100
From: Norbert Melzer <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] garbage collected object
Message-ID:
<CA+bCVssYW4fQbp2DrHu05_Q64aPy40xuXGd5t-virUog=ox...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
If you know enough about an object to find it on the heap, then you hold a
reference, if you hold a reference, then it's probably not gced...
Am 14.01.2015 11:24 schrieb "Elise Huard" <[email protected]>:
> Hi,
>
> Maybe a stupid question: is there a way to check whether a particular
> data structure (or set of data structures) has been garbage collected?
> Or indirectly: is there a way to check what's still alive in the heap,
> so that you can potentially diff from one moment to another?
> Thanks,
>
> Elise Huard
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
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Message: 2
Date: Wed, 14 Jan 2015 07:17:33 -0500
From: Ryan Trinkle <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] garbage collected object
Message-ID:
<cahnepiz121nlwefm6jffoq-qqro8qwxzk+ndsjwk0tvu-y3...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
You can use the 'vacuum' package to explore the heap, and you can use
System.Mem.Weak to create a reference to something that won't keep it from
being GCed and will let you check on it later. You can also use the
built-in heap profiling capabilities to track things like the memory usage
of the entire heap from moment to moment.
On Wed, Jan 14, 2015 at 5:24 AM, Elise Huard <[email protected]> wrote:
> Hi,
>
> Maybe a stupid question: is there a way to check whether a particular
> data structure (or set of data structures) has been garbage collected?
> Or indirectly: is there a way to check what's still alive in the heap,
> so that you can potentially diff from one moment to another?
> Thanks,
>
> Elise Huard
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
>
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Message: 3
Date: Wed, 14 Jan 2015 12:54:34 +0000 (UTC)
From: Abhinav Kalawatia <[email protected]>
To: "[email protected]" <[email protected]>
Subject: [Haskell-beginners] Error while trying to install ByteString
Package
Message-ID:
<1496218722.1011416.1421240074267.javamail.ya...@jws10604.mail.bf1.yahoo.com>
Content-Type: text/plain; charset="utf-8"
Hi,?I get the following error while I tried installing the ByteString package.
Could you please help me resolve
this?>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>
C:\Users> cabal install bytestring
Resolving dependencies...
Configuring bytestring-0.10.4.1...
Failed to install bytestring-0.10.4.1
Last 10 lines of the build log ( C:\Users\AppData\Roaming\caba
l\logs\bytestring-0.10.4.1.log ):
setup-Cabal-1.18.1.3-i386-windows-ghc-7.8.3.exe: Missing dependency on a
foreign library:
* Missing (or bad) header file: fpstring.h
This problem can usually be solved by installing the system package that
provides this library (you may need the "-dev" version). If the library is
already installed but in a non-standard location then you can use the flags
--extra-include-dirs= and --extra-lib-dirs= to specify where it is.
If the header file does exist, it may contain errors that are caught by the C
compiler at the preprocessing stage. In this case you can re-run configure
with the verbosity flag -v3 to see the error messages.
cabal: Error: some packages failed to install:
bytestring-0.10.4.1 failed during the configure step. The exception was:
ExitFailure
1>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>>?Regards,Abhinav?
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Message: 4
Date: Thu, 15 Jan 2015 12:51:37 +0100
From: Miro Karpis <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: [Haskell-beginners] help with IO guards
Message-ID:
<cajnnbxfoypxd2d53u__vvlhcbbleqj1pqbdcovq9ynder6h...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
Hi,
please is there a way to have guards with 'where' that communicates with
IO? Or is there some other more elegant way? I can do this with classic
if/else,...but I just find it nicer with guards.
I have something like this (just an example):
f :: Int -> IO String
f x
| null dbOutput = return "no db record"
| otherwise = return "we got some db records"
where dbOutput = getDBRecord x
getDBRecord :: Int -> IO [Int]
getDBRecord recordId = do
putStrLn $ "checking dbRecord" ++ show recordId
--getting data from DB
return [1,2]
problem is that db dbOutput is IO and the guard check does not like it:
Couldn't match expected type ?[a0]? with actual type ?IO [Int]?
In the first argument of ?null?, namely ?dbOutput?
In the expression: null dbOutput
Cheers,
Miro
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