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Today's Topics:
1. Re: QuickCheck Crazy (Brandon Allbery)
2. Re: QuickCheck Crazy (Dimitri DeFigueiredo)
3. Re: QuickCheck Crazy (Brandon Allbery)
4. Re: QuickCheck Crazy (Dimitri DeFigueiredo)
5. Re: latest Haskell Platform build fails (Heinrich Apfelmus)
----------------------------------------------------------------------
Message: 1
Date: Fri, 17 Oct 2014 09:59:54 -0400
From: Brandon Allbery <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] QuickCheck Crazy
Message-ID:
<CAKFCL4Uvr=yUOcr6m6ivZgT8tjMy-g3p6WTJN=_=oaagkk7...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Fri, Oct 17, 2014 at 1:53 AM, Dimitri DeFigueiredo <
[email protected]> wrote:
> This makes more sense now. It does still seem like very unsafe default
> behavior by quickCheck.
QuickCheck has no way of knowing that ghci has ExtendedDefaultRules
enabled, and (quite aside from the difficulty of doing type-case in
Haskell) I'm not sure that arbitrarily declaring types involving () to be
user error is a good idea.
--
brandon s allbery kf8nh sine nomine associates
[email protected] [email protected]
unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
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Message: 2
Date: Fri, 17 Oct 2014 12:55:20 -0600
From: Dimitri DeFigueiredo <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] QuickCheck Crazy
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"
I agree we have to pick a poison here and I didn't know that the
Extended Default Rules were the culprit, but I think the end result is
scary because forgetting a type signature is about the most common
mistake I make. Having that imply that tests will silently pass means
(to me) that it's not safe to use Quickcheck with GHCi. Or, just
remember to always make properties monomorphic. "Always!"
I would be much more comfortable using quickCheck' the version where ()
implies user error, as you suggested. For me that is an enhacement to
quickCheck that allows it to be used in GHCi, but that is just my opinion.
In any case, thanks for shedding more light on the reasons behind the
design.
Dimitri
On 17/10/14 07:59, Brandon Allbery wrote:
> On Fri, Oct 17, 2014 at 1:53 AM, Dimitri DeFigueiredo
> <[email protected] <mailto:[email protected]>> wrote:
>
> This makes more sense now. It does still seem like very unsafe
> default behavior by quickCheck.
>
>
> QuickCheck has no way of knowing that ghci has ExtendedDefaultRules
> enabled, and (quite aside from the difficulty of doing type-case in
> Haskell) I'm not sure that arbitrarily declaring types involving () to
> be user error is a good idea.
>
> --
> brandon s allbery kf8nh sine nomine associates
> [email protected] <mailto:[email protected]>
> [email protected] <mailto:[email protected]>
> unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
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Message: 3
Date: Fri, 17 Oct 2014 15:16:57 -0400
From: Brandon Allbery <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] QuickCheck Crazy
Message-ID:
<CAKFCL4UmzO9xi2dH8=mHkoPLwGvcU9nvmh0SW5W=y8zb5wp...@mail.gmail.com>
Content-Type: text/plain; charset="utf-8"
On Fri, Oct 17, 2014 at 2:55 PM, Dimitri DeFigueiredo <
[email protected]> wrote:
> I agree we have to pick a poison here and I didn't know that the Extended
> Default Rules were the culprit, but I think the end result is scary because
> forgetting a type signature is about the most common mistake I make. Having
> that imply that tests will silently pass means (to me) that it's not safe
> to use Quickcheck with GHCi. Or, just remember to always make properties
> monomorphic. "Always!"
>
It might make more sense to have a warning in the QuickCheck documentation
that, from ghci, it's best to ":seti -XNoExtendedDefaultRules" (and/or add
that to .ghci / ghci.ini) to avoid surprises.
--
brandon s allbery kf8nh sine nomine associates
[email protected] [email protected]
unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
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Message: 4
Date: Fri, 17 Oct 2014 14:05:38 -0600
From: Dimitri DeFigueiredo <[email protected]>
To: The Haskell-Beginners Mailing List - Discussion of primarily
beginner-level topics related to Haskell <[email protected]>
Subject: Re: [Haskell-beginners] QuickCheck Crazy
Message-ID: <[email protected]>
Content-Type: text/plain; charset="windows-1252"; Format="flowed"
That is a great idea! I'm changing my ghci configuration as I write
this. Problem solved!
Thanks,
Dimitri
On 17/10/14 13:16, Brandon Allbery wrote:
> On Fri, Oct 17, 2014 at 2:55 PM, Dimitri DeFigueiredo
> <[email protected] <mailto:[email protected]>> wrote:
>
> I agree we have to pick a poison here and I didn't know that the
> Extended Default Rules were the culprit, but I think the end
> result is scary because forgetting a type signature is about the
> most common mistake I make. Having that imply that tests will
> silently pass means (to me) that it's not safe to use Quickcheck
> with GHCi. Or, just remember to always make properties
> monomorphic. "Always!"
>
>
> It might make more sense to have a warning in the QuickCheck
> documentation that, from ghci, it's best to ":seti
> -XNoExtendedDefaultRules" (and/or add that to .ghci / ghci.ini) to
> avoid surprises.
>
> --
> brandon s allbery kf8nh sine nomine associates
> [email protected] <mailto:[email protected]>
> [email protected] <mailto:[email protected]>
> unix, openafs, kerberos, infrastructure, xmonad http://sinenomine.net
>
>
> _______________________________________________
> Beginners mailing list
> [email protected]
> http://www.haskell.org/mailman/listinfo/beginners
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Message: 5
Date: Sat, 18 Oct 2014 09:31:44 +0200
From: Heinrich Apfelmus <[email protected]>
To: [email protected]
Subject: Re: [Haskell-beginners] latest Haskell Platform build fails
Message-ID: <[email protected]>
Content-Type: text/plain; charset=UTF-8; format=flowed
Michael L Martin wrote:
> On 10/16/2014 03:11 PM, Mateusz Kowalczyk wrote:
>> Merely going from the error message and your steps, it seems to me that
>> you're *not* meant to install GHC yourself first and that the platform
>> ships with GHC. I would say try again but without installing GHC and
>> cabal first.
>>
>>
> Well, that didn't work, either:
>
> mmartin@cloud:~/Downloads/haskell-platform-2014.2.0.0$ ./platform.sh
> .../ghc-7.8.3-x86_64-unknown-linux-deb7.tar.bz2
> ../platform.sh: 18: ./platform.sh: cabal: not found
> ***
> *** Building hptool
> ***
> ../platform.sh: 29: ./platform.sh: cabal: not found
> mmartin@cloud:~/Downloads/haskell-platform-2014.2.0.0$
Apparently, different distributions of the Haskell Platform differ in
what tools they package: the binary distribution includes GHC and cabal,
whereas the source distribution, which you are currently trying to
install, doesn't include GHC and cabal.
Judging from the error message
> Stderr:
> mtl-2.1.3.1: package(s) with this id already exist: mtl-2.1.3.1
it seems that the platform tries to build the `mtl` package, but fails
because it is already installed. You can use the command
$ ghc-pkg list
to see which packages are installed globally and in your home directory.
Most likely, `mtl` got installed because you installed `cabal-install`.
I have no idea how to deal with the conflict, though, I'm not really
familiar with the Haskell platform source distribution.
Best regards,
Heinrich Apfelmus
--
http://apfelmus.nfshost.com
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