Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
I think I need to think this through
On Thu, Jun 14, 2012 at 12:28 PM, Ivan Lazar Miljenovic
wrote:
> On 14 June 2012 14:20, Magicloud Magiclouds
> wrote:
>> OK. I think I understand a little.
>> I use Job here just wants to simplify the code. And since I provide
>> the function as library, I cannot decide what exact type k is. What
>> should I do?
>
> Do you know what the type of `a'? If so:
>
> type Job k = Map k String
>
> Otherwise... do you even need a type alias?
>
>>
>> On Thu, Jun 14, 2012 at 11:23 AM, Arlen Cuss wrote:
>>> (resending to café, turns out I wasn't subbed from this address.)
>>>
>>> Hi Magicloud,
>>> This is correct; because you've hidden the type-variables away by
>>> universally quantifying them, there's no more level of specificity you can
>>> get back *out* of them than just "some kind of Map" (Job = M.Map k b, where
>>> k ≠ k0, b ≠ b0).
>>>
>>> If you have a Job type which can store *any* kind of Map (forall k a. Job
>>> (Map k a)), then that means you could have a Job with a Map Int Bool, and a
>>> Job with a Map String (Float -> Float), and they'd both have the same type
>>> "Job". You can't do anything with the values within, because you're being
>>> too permissive about what a Job is.
>>>
>>> You may want "data Job k a = Job (Map k a)", *or* if you do actually use
>>> one kind of Map only, then why not "data Job = Job (Map Int String)"
>>> (substituting your real types for Int and String). In this case, you could
>>> also consider using newtype ("newtype Job = Job { getJob :: Map Int String
>>> }") to provide the guarantee that you're getting a Job (and not any Map Int
>>> String) without performance loss.
>>>
>>> Let me know if I've been more confusing than helpful;
>>>
>>> Arlen
>>>
>>>
>>> On Thursday, 14 June 2012 at 1:16 PM, Magicloud Magiclouds wrote:
>>>
Hi there,
Thanks for the reply. To be clear, all I want is to "avoid having to
type type variables all over the place". What should I do? My original
code with RankNTypes and ImpredicativeTypes does not work
The "type Job = forall k a. M.Map k a" works now. But function uses
it does not. Compiler complains about "Couldn't match expected type
`Job' with actual type `M.Map k0 b0'".
On Wed, Jun 13, 2012 at 9:15 PM, Daniel Peebles >>> (mailto:pumpkin...@gmail.com)> wrote:
That doesn't require existential quantification, but it'll need Rank-2
typesif you ever do anything with Job. Unfortunately, a universally
quantifiedJob like what you wrote (or what Magicloud seems to want) is
only inhabitedby the empty Map.
>
An existentially quantified Job, as you might get with
>
data Job = forall k a. Job (Map k a)
>
does let you wrap up any Map containing anything in it, but
unfortunatelythe only thing you can do with that map afterwards is ask for
"structural"properties about it, like whether it's empty or how many
elements it has init. You could ask to enumerate the elements in it, but
you wouldn't be ableto touch any of them because you wouldn't know what
their types were.
>
So I'm not really sure how to interpret the question. Was the goal to have
aheterogeneous Map, maybe? Or just to avoid having to type type variables
allover the place? Both of those are possible but require a bit
moresophistication with types.
>
-Dan
>
>
On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa
Paletmailto:ifiguer...@gmail.com)> wrote:
> >
Do you want to hide the specific types of the job? Presumably to
thendefine a type JobList = [Job] ?You can do that with the
ExistentialQuantification extension.
> >
type Job = forall k a. Map k atype JobList = [Job]
> >
??Note you can't unpack the types k a once you have hidden them. But
thetypechecker can use it to ensure some static property.Also you could
use unsafeCoerce to do some casts, but *only if you are*sure* that things
will go OK*.
> >
> >
2012/6/13 Magicloud Magiclouds >>> (mailto:magicloud.magiclo...@gmail.com)>
> > >
Hi,I've forgotten this.This is OK:type Job k a = Map k aAnd this is OK:{-#
LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?type Job = forall a.
forall k. Map k a
> > >
Then how to write it like this?type Job = Map k a--竹密岂妨流水过山高哪阻野云飞
> > >
And for G+, please use magiclouds#gmail.com (http://gmail.com).
> > >
___Haskell-Cafe mailing
listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
> > > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
> >
> >
> >
> >
> >
> >
> >
--Ismael
> >
> >
___Haskell-Cafe mailing
listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
>>
Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
On 14 June 2012 14:20, Magicloud Magiclouds
wrote:
> OK. I think I understand a little.
> I use Job here just wants to simplify the code. And since I provide
> the function as library, I cannot decide what exact type k is. What
> should I do?
Do you know what the type of `a'? If so:
type Job k = Map k String
Otherwise... do you even need a type alias?
>
> On Thu, Jun 14, 2012 at 11:23 AM, Arlen Cuss wrote:
>> (resending to café, turns out I wasn't subbed from this address.)
>>
>> Hi Magicloud,
>> This is correct; because you've hidden the type-variables away by
>> universally quantifying them, there's no more level of specificity you can
>> get back *out* of them than just "some kind of Map" (Job = M.Map k b, where
>> k ≠ k0, b ≠ b0).
>>
>> If you have a Job type which can store *any* kind of Map (forall k a. Job
>> (Map k a)), then that means you could have a Job with a Map Int Bool, and a
>> Job with a Map String (Float -> Float), and they'd both have the same type
>> "Job". You can't do anything with the values within, because you're being
>> too permissive about what a Job is.
>>
>> You may want "data Job k a = Job (Map k a)", *or* if you do actually use one
>> kind of Map only, then why not "data Job = Job (Map Int String)"
>> (substituting your real types for Int and String). In this case, you could
>> also consider using newtype ("newtype Job = Job { getJob :: Map Int String
>> }") to provide the guarantee that you're getting a Job (and not any Map Int
>> String) without performance loss.
>>
>> Let me know if I've been more confusing than helpful;
>>
>> Arlen
>>
>>
>> On Thursday, 14 June 2012 at 1:16 PM, Magicloud Magiclouds wrote:
>>
>>> Hi there,
>>> Thanks for the reply. To be clear, all I want is to "avoid having to
>>> type type variables all over the place". What should I do? My original
>>> code with RankNTypes and ImpredicativeTypes does not work
>>>
>>> The "type Job = forall k a. M.Map k a" works now. But function uses
>>> it does not. Compiler complains about "Couldn't match expected type
>>> `Job' with actual type `M.Map k0 b0'".
>>>
>>> On Wed, Jun 13, 2012 at 9:15 PM, Daniel Peebles >> (mailto:pumpkin...@gmail.com)> wrote:
>>> That doesn't require existential quantification, but it'll need Rank-2
>>> typesif you ever do anything with Job. Unfortunately, a universally
>>> quantifiedJob like what you wrote (or what Magicloud seems to want) is only
>>> inhabitedby the empty Map.
>>> >
>>> An existentially quantified Job, as you might get with
>>> >
>>> data Job = forall k a. Job (Map k a)
>>> >
>>> does let you wrap up any Map containing anything in it, but
>>> unfortunatelythe only thing you can do with that map afterwards is ask for
>>> "structural"properties about it, like whether it's empty or how many
>>> elements it has init. You could ask to enumerate the elements in it, but
>>> you wouldn't be ableto touch any of them because you wouldn't know what
>>> their types were.
>>> >
>>> So I'm not really sure how to interpret the question. Was the goal to have
>>> aheterogeneous Map, maybe? Or just to avoid having to type type variables
>>> allover the place? Both of those are possible but require a bit
>>> moresophistication with types.
>>> >
>>> -Dan
>>> >
>>> >
>>> On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa Palet>> (mailto:ifiguer...@gmail.com)> wrote:
>>> > >
>>> Do you want to hide the specific types of the job? Presumably to thendefine
>>> a type JobList = [Job] ?You can do that with the ExistentialQuantification
>>> extension.
>>> > >
>>> type Job = forall k a. Map k atype JobList = [Job]
>>> > >
>>> ??Note you can't unpack the types k a once you have hidden them. But
>>> thetypechecker can use it to ensure some static property.Also you could use
>>> unsafeCoerce to do some casts, but *only if you are*sure* that things will
>>> go OK*.
>>> > >
>>> > >
>>> 2012/6/13 Magicloud Magiclouds >> (mailto:magicloud.magiclo...@gmail.com)>
>>> > > >
>>> Hi,I've forgotten this.This is OK:type Job k a = Map k aAnd this is OK:{-#
>>> LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?type Job = forall a.
>>> forall k. Map k a
>>> > > >
>>> Then how to write it like this?type Job = Map k a--竹密岂妨流水过山高哪阻野云飞
>>> > > >
>>> And for G+, please use magiclouds#gmail.com (http://gmail.com).
>>> > > >
>>> ___Haskell-Cafe mailing
>>> listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
>>> > > > http://www.haskell.org/mailman/listinfo/haskell-cafe
>>> > >
>>> > >
>>> > >
>>> > >
>>> > >
>>> > >
>>> > >
>>> > >
>>> --Ismael
>>> > >
>>> > >
>>> ___Haskell-Cafe mailing
>>> listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
>>> > > http://www.haskell.org/mailman/listinfo/haskell-cafe
>>> >
>>>
>>>
>>>
>>>
>>>
>>>
>>>
>>> --
>>> 竹密岂妨流水过
>>> 山高哪阻野云飞
>>>
>>> And for G+, please use magiclouds#gmail.com (http://gmail.com).
>>>
>>>
Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
OK. I think I understand a little.
I use Job here just wants to simplify the code. And since I provide
the function as library, I cannot decide what exact type k is. What
should I do?
On Thu, Jun 14, 2012 at 11:23 AM, Arlen Cuss wrote:
> (resending to café, turns out I wasn't subbed from this address.)
>
> Hi Magicloud,
> This is correct; because you've hidden the type-variables away by universally
> quantifying them, there's no more level of specificity you can get back *out*
> of them than just "some kind of Map" (Job = M.Map k b, where k ≠ k0, b ≠ b0).
>
> If you have a Job type which can store *any* kind of Map (forall k a. Job
> (Map k a)), then that means you could have a Job with a Map Int Bool, and a
> Job with a Map String (Float -> Float), and they'd both have the same type
> "Job". You can't do anything with the values within, because you're being too
> permissive about what a Job is.
>
> You may want "data Job k a = Job (Map k a)", *or* if you do actually use one
> kind of Map only, then why not "data Job = Job (Map Int String)"
> (substituting your real types for Int and String). In this case, you could
> also consider using newtype ("newtype Job = Job { getJob :: Map Int String
> }") to provide the guarantee that you're getting a Job (and not any Map Int
> String) without performance loss.
>
> Let me know if I've been more confusing than helpful;
>
> Arlen
>
>
> On Thursday, 14 June 2012 at 1:16 PM, Magicloud Magiclouds wrote:
>
>> Hi there,
>> Thanks for the reply. To be clear, all I want is to "avoid having to
>> type type variables all over the place". What should I do? My original
>> code with RankNTypes and ImpredicativeTypes does not work
>>
>> The "type Job = forall k a. M.Map k a" works now. But function uses
>> it does not. Compiler complains about "Couldn't match expected type
>> `Job' with actual type `M.Map k0 b0'".
>>
>> On Wed, Jun 13, 2012 at 9:15 PM, Daniel Peebles > (mailto:pumpkin...@gmail.com)> wrote:
>> That doesn't require existential quantification, but it'll need Rank-2
>> typesif you ever do anything with Job. Unfortunately, a universally
>> quantifiedJob like what you wrote (or what Magicloud seems to want) is only
>> inhabitedby the empty Map.
>> >
>> An existentially quantified Job, as you might get with
>> >
>> data Job = forall k a. Job (Map k a)
>> >
>> does let you wrap up any Map containing anything in it, but unfortunatelythe
>> only thing you can do with that map afterwards is ask for
>> "structural"properties about it, like whether it's empty or how many
>> elements it has init. You could ask to enumerate the elements in it, but you
>> wouldn't be ableto touch any of them because you wouldn't know what their
>> types were.
>> >
>> So I'm not really sure how to interpret the question. Was the goal to have
>> aheterogeneous Map, maybe? Or just to avoid having to type type variables
>> allover the place? Both of those are possible but require a bit
>> moresophistication with types.
>> >
>> -Dan
>> >
>> >
>> On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa Palet> (mailto:ifiguer...@gmail.com)> wrote:
>> > >
>> Do you want to hide the specific types of the job? Presumably to thendefine
>> a type JobList = [Job] ?You can do that with the ExistentialQuantification
>> extension.
>> > >
>> type Job = forall k a. Map k atype JobList = [Job]
>> > >
>> ??Note you can't unpack the types k a once you have hidden them. But
>> thetypechecker can use it to ensure some static property.Also you could use
>> unsafeCoerce to do some casts, but *only if you are*sure* that things will
>> go OK*.
>> > >
>> > >
>> 2012/6/13 Magicloud Magiclouds > (mailto:magicloud.magiclo...@gmail.com)>
>> > > >
>> Hi,I've forgotten this.This is OK:type Job k a = Map k aAnd this is OK:{-#
>> LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?type Job = forall a.
>> forall k. Map k a
>> > > >
>> Then how to write it like this?type Job = Map k a--竹密岂妨流水过山高哪阻野云飞
>> > > >
>> And for G+, please use magiclouds#gmail.com (http://gmail.com).
>> > > >
>> ___Haskell-Cafe mailing
>> listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
>> > > > http://www.haskell.org/mailman/listinfo/haskell-cafe
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> > >
>> --Ismael
>> > >
>> > >
>> ___Haskell-Cafe mailing
>> listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
>> > > http://www.haskell.org/mailman/listinfo/haskell-cafe
>> >
>>
>>
>>
>>
>>
>>
>>
>> --
>> 竹密岂妨流水过
>> 山高哪阻野云飞
>>
>> And for G+, please use magiclouds#gmail.com (http://gmail.com).
>>
>> ___
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org (mailto:Haskell-Cafe@haskell.org)
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/
[Haskell-cafe] ANNOUNCE: uuid-1.2.6
Hi folks, I'm happy to announce a new point release of the uuid library, 1.2.6: http://hackage.haskell.org/package/uuid-1.2.6 The 'uuid' package implements most of RFC 4122[1] including random generation and generation based on hardware MAC addresses. I haven't announced a point-release in a while. The changes since 1.2.1 include: * When generating UUIDs from the hardware MAC address, if the MAC address is not available we now use a random seed for our (hidden, global) state machine * The 'Read' instance now drops leading spaces * Added the functions 'toWords' and 'fromWords', primary to support the package uuid-quasi[2]. Take care, Antoine 1: http://tools.ietf.org/html/rfc4122 2: http://hackage.haskell.org/package/uuid-quasi ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
(resending to café, turns out I wasn't subbed from this address.)
Hi Magicloud,
This is correct; because you've hidden the type-variables away by universally
quantifying them, there's no more level of specificity you can get back *out*
of them than just "some kind of Map" (Job = M.Map k b, where k ≠ k0, b ≠ b0).
If you have a Job type which can store *any* kind of Map (forall k a. Job (Map
k a)), then that means you could have a Job with a Map Int Bool, and a Job with
a Map String (Float -> Float), and they'd both have the same type "Job". You
can't do anything with the values within, because you're being too permissive
about what a Job is.
You may want "data Job k a = Job (Map k a)", *or* if you do actually use one
kind of Map only, then why not "data Job = Job (Map Int String)" (substituting
your real types for Int and String). In this case, you could also consider
using newtype ("newtype Job = Job { getJob :: Map Int String }") to provide the
guarantee that you're getting a Job (and not any Map Int String) without
performance loss.
Let me know if I've been more confusing than helpful;
Arlen
On Thursday, 14 June 2012 at 1:16 PM, Magicloud Magiclouds wrote:
> Hi there,
> Thanks for the reply. To be clear, all I want is to "avoid having to
> type type variables all over the place". What should I do? My original
> code with RankNTypes and ImpredicativeTypes does not work
>
> The "type Job = forall k a. M.Map k a" works now. But function uses
> it does not. Compiler complains about "Couldn't match expected type
> `Job' with actual type `M.Map k0 b0'".
>
> On Wed, Jun 13, 2012 at 9:15 PM, Daniel Peebles (mailto:pumpkin...@gmail.com)> wrote:
> That doesn't require existential quantification, but it'll need Rank-2
> typesif you ever do anything with Job. Unfortunately, a universally
> quantifiedJob like what you wrote (or what Magicloud seems to want) is only
> inhabitedby the empty Map.
> >
> An existentially quantified Job, as you might get with
> >
> data Job = forall k a. Job (Map k a)
> >
> does let you wrap up any Map containing anything in it, but unfortunatelythe
> only thing you can do with that map afterwards is ask for
> "structural"properties about it, like whether it's empty or how many elements
> it has init. You could ask to enumerate the elements in it, but you wouldn't
> be ableto touch any of them because you wouldn't know what their types were.
> >
> So I'm not really sure how to interpret the question. Was the goal to have
> aheterogeneous Map, maybe? Or just to avoid having to type type variables
> allover the place? Both of those are possible but require a bit
> moresophistication with types.
> >
> -Dan
> >
> >
> On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa Palet (mailto:ifiguer...@gmail.com)> wrote:
> > >
> Do you want to hide the specific types of the job? Presumably to thendefine a
> type JobList = [Job] ?You can do that with the ExistentialQuantification
> extension.
> > >
> type Job = forall k a. Map k atype JobList = [Job]
> > >
> ??Note you can't unpack the types k a once you have hidden them. But
> thetypechecker can use it to ensure some static property.Also you could use
> unsafeCoerce to do some casts, but *only if you are*sure* that things will go
> OK*.
> > >
> > >
> 2012/6/13 Magicloud Magiclouds (mailto:magicloud.magiclo...@gmail.com)>
> > > >
> Hi,I've forgotten this.This is OK:type Job k a = Map k aAnd this is OK:{-#
> LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?type Job = forall a. forall
> k. Map k a
> > > >
> Then how to write it like this?type Job = Map k a--竹密岂妨流水过山高哪阻野云飞
> > > >
> And for G+, please use magiclouds#gmail.com (http://gmail.com).
> > > >
> ___Haskell-Cafe mailing
> listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
> > > > http://www.haskell.org/mailman/listinfo/haskell-cafe
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> > >
> --Ismael
> > >
> > >
> ___Haskell-Cafe mailing
> listhaskell-c...@haskell.org (mailto:Haskell-Cafe@haskell.org)
> > > http://www.haskell.org/mailman/listinfo/haskell-cafe
> >
>
>
>
>
>
>
>
> --
> 竹密岂妨流水过
> 山高哪阻野云飞
>
> And for G+, please use magiclouds#gmail.com (http://gmail.com).
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org (mailto:Haskell-Cafe@haskell.org)
> http://www.haskell.org/mailman/listinfo/haskell-cafe
___
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Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
Hi there,
Thanks for the reply. To be clear, all I want is to "avoid having to
type type variables all over the place". What should I do? My original
code with RankNTypes and ImpredicativeTypes does not work
The "type Job = forall k a. M.Map k a" works now. But function uses
it does not. Compiler complains about "Couldn't match expected type
`Job' with actual type `M.Map k0 b0'".
On Wed, Jun 13, 2012 at 9:15 PM, Daniel Peebles wrote:
> That doesn't require existential quantification, but it'll need Rank-2 types
> if you ever do anything with Job. Unfortunately, a universally quantified
> Job like what you wrote (or what Magicloud seems to want) is only inhabited
> by the empty Map.
>
> An existentially quantified Job, as you might get with
>
> data Job = forall k a. Job (Map k a)
>
> does let you wrap up any Map containing anything in it, but unfortunately
> the only thing you can do with that map afterwards is ask for "structural"
> properties about it, like whether it's empty or how many elements it has in
> it. You could ask to enumerate the elements in it, but you wouldn't be able
> to touch any of them because you wouldn't know what their types were.
>
> So I'm not really sure how to interpret the question. Was the goal to have a
> heterogeneous Map, maybe? Or just to avoid having to type type variables all
> over the place? Both of those are possible but require a bit more
> sophistication with types.
>
> -Dan
>
>
> On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa Palet
> wrote:
>>
>> Do you want to hide the specific types of the job? Presumably to then
>> define a type JobList = [Job] ?
>> You can do that with the ExistentialQuantification extension.
>>
>> type Job = forall k a. Map k a
>> type JobList = [Job]
>>
>> ??
>> Note you can't unpack the types k a once you have hidden them. But the
>> typechecker can use it to ensure some static property.
>> Also you could use unsafeCoerce to do some casts, but *only if you are
>> *sure* that things will go OK*.
>>
>>
>> 2012/6/13 Magicloud Magiclouds
>>>
>>> Hi,
>>> I've forgotten this.
>>> This is OK:
>>> type Job k a = Map k a
>>> And this is OK:
>>> {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
>>> type Job = forall a. forall k. Map k a
>>>
>>> Then how to write it like this?
>>> type Job = Map k a
>>> --
>>> 竹密岂妨流水过
>>> 山高哪阻野云飞
>>>
>>> And for G+, please use magiclouds#gmail.com.
>>>
>>> ___
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe@haskell.org
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>
>>
>>
>> --
>> Ismael
>>
>>
>> ___
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
--
竹密岂妨流水过
山高哪阻野云飞
And for G+, please use magiclouds#gmail.com.
___
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[Haskell-cafe] Haskell Weekly News: Issue 231
Welcome to issue 231 of the HWN, an issue covering crowd-sourced bits of information about Haskell from around the web. This issue covers the week of June 03 to 09, 2012. Announcements Paolo Capriotti announced the patchlevel release of GHC 7.4.2. "This release contains a number of bugfixes relative to 7.4.1, so we recommend upgrading." [1] http://goo.gl/X3Z85 Quotes of the Week * roconnor: there's a right way, and a wrong way, and then there is the ekmett way. Top Reddit Stories * Haskell Platform 2012.2.0.0 released Domain: hackage.haskell.org, Score: 104, Comments: 33 On Reddit: [2] http://goo.gl/ZNa9h Original: [3] http://goo.gl/JjJg2 * Why free monads matter Domain: haskellforall.com, Score: 61, Comments: 47 On Reddit: [4] http://goo.gl/hfKlc Original: [5] http://goo.gl/JPpsp * 3 Flavors of MVar: Lock, Var, Barrier Domain: neilmitchell.blogspot.com, Score: 43, Comments: 20 On Reddit: [6] http://goo.gl/3eEkO Original: [7] http://goo.gl/ek7Qq * Introducing the HERMIT Equational Reasoning Framework Domain: ittc.ku.edu, Score: 36, Comments: 20 On Reddit: [8] http://goo.gl/UC0sF Original: [9] http://goo.gl/ifS7f * Complicating conduit? Domain: yesodweb.com, Score: 35, Comments: 45 On Reddit: [10] http://goo.gl/W4rfE Original: [11] http://goo.gl/rU0vK * Beautiful Code, Compelling Evidence: OpenGL, Cairo tutorial [PDF, 33 pages] Domain: renci.org, Score: 33, Comments: 2 On Reddit: [12] http://goo.gl/qKY8w Original: [13] http://goo.gl/r5SVj * Forklift - a pattern for performing monadic actions in a worker thread Domain: apfelmus.nfshost.com, Score: 30, Comments: 7 On Reddit: [14] http://goo.gl/B6brV Original: [15] http://goo.gl/mWVAv * Dependently typed programming with singletons (Eisenberg, Weirich)[PDF] Domain: cis.upenn.edu, Score: 29, Comments: 3 On Reddit: [16] http://goo.gl/y3fYv Original: [17] http://goo.gl/RqM5m * Continuation-based relative-time FRP Domain: paolocapriotti.com, Score: 22, Comments: 6 On Reddit: [18] http://goo.gl/CFSK7 Original: [19] http://goo.gl/cP0cJ * Explaining the Prompt monad with a clearer representation Domain: joeysmandatory.blogspot.com, Score: 21, Comments: 42 On Reddit: [20] http://goo.gl/ZZM93 Original: [21] http://goo.gl/Im7SF * Lazily Evaluate length of a list Domain: self.haskell, Score: 21, Comments: 29 On Reddit: [22] http://goo.gl/cKUOt Original: [23] http://goo.gl/cKUOt Top StackOverflow Questions * Killing a thread when MVar is garbage collected votes: 22, answers: 4 Read on SO: [24] http://goo.gl/cvoqw * How does one write efficient Dynamic Programming algorithms in Haskell? votes: 16, answers: 3 Read on SO: [25] http://goo.gl/mkMTp * How to apply a polymorphic function to a Dynamic value votes: 11, answers: 1 Read on SO: [26] http://goo.gl/3jIVr * Haskell Typeclass for Tuples votes: 11, answers: 3 Read on SO: [27] http://goo.gl/pvDah * Monadic expressions in conditionals - GHC compiles, cabal refuses votes: 10, answers: 2 Read on SO: [28] http://goo.gl/QXMXh * GHC Optimization: Collatz conjecture votes: 10, answers: 2 Read on SO: [29] http://goo.gl/AfiEC * Haskell: Lists vs Streams votes: 10, answers: 3 Read on SO: [30] http://goo.gl/qn1dE * Is my program Turing-complete? votes: 9, answers: 2 Read on SO: [31] http://goo.gl/PLf5q * How to find the optimal processing order? votes: 9, answers: 1 Read on SO: [32] http://goo.gl/P3XZ2 * How to do fast data deserialization in Haskell votes: 9, answers: 1 Read on SO: [33] http://goo.gl/Synm2 * What's so bad about OverlappingInstances? votes: 9, answers: 1 Read on SO: [34] http://goo.gl/M17Rp Until next time, Daniel Santa Cruz References 1. http://permalink.gmane.org/gmane.comp.lang.haskell.glasgow.user/22181 2. http://hackage.haskell.org/platform/?2012.2.0.0 3. http://www.reddit.com/r/haskell/comments/uipvz/haskell_platform_2012200_released/ 4. http://www.haskellforall.com/2012/06/you-could-have-invented-free-monads.html 5. http://www.reddit.com/r/haskell/comments/utxq2/why_free_monads_matter/ 6. http://neilmitchell.blogspot.com/2012/06/flavours-of-mvar_04.html 7. http://www.reddit.com/r/haskell/comments/uk9wu/3_flavors_of_mvar_lock_var_barrier/ 8. http://www.ittc.ku.edu/csdlblog/?p=105 9. http://www.reddit.com/r/haskell/comments/ujdet/introducing_the_hermit_equational_reasoning/ 10. http://www.yesodweb.com/blog/2012/06/complicating-conduit 11. http://www.reddit.com/r/haskell/comments/urc75/complicating_conduit/ 12. http://www.renci.org/wp-content/pub/tutorials/BeautifulCode.pdf 13. http://www.reddit.com/r/haskell/comments/uqc33/beautiful_code_compelling_evidence_opengl_cairo/ 14. http://
Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
Thank you all. I just want to wrap some complex types.
So I learn from all info above, I still have to use forall explicitly
On Wed, Jun 13, 2012 at 9:19 PM, Yves Parès wrote:
> Mmmmh... no, to do that you need ImpredicativeTypes (which is I believe
> about to be deprecated).
> You have to declare Job a data, not a type, and use
> ExistentialQuantification.
>
>
> 2012/6/13 Ismael Figueroa Palet
>>
>> Do you want to hide the specific types of the job? Presumably to then
>> define a type JobList = [Job] ?
>> You can do that with the ExistentialQuantification extension.
>>
>> type Job = forall k a. Map k a
>> type JobList = [Job]
>>
>> ??
>> Note you can't unpack the types k a once you have hidden them. But the
>> typechecker can use it to ensure some static property.
>> Also you could use unsafeCoerce to do some casts, but *only if you are
>> *sure* that things will go OK*.
>>
>>
>> 2012/6/13 Magicloud Magiclouds
>>>
>>> Hi,
>>> I've forgotten this.
>>> This is OK:
>>> type Job k a = Map k a
>>> And this is OK:
>>> {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
>>> type Job = forall a. forall k. Map k a
>>>
>>> Then how to write it like this?
>>> type Job = Map k a
>>> --
>>> 竹密岂妨流水过
>>> 山高哪阻野云飞
>>>
>>> And for G+, please use magiclouds#gmail.com.
>>>
>>> ___
>>> Haskell-Cafe mailing list
>>> Haskell-Cafe@haskell.org
>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>>
>>
>>
>> --
>> Ismael
>>
>>
>> ___
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
--
竹密岂妨流水过
山高哪阻野云飞
And for G+, please use magiclouds#gmail.com.
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Re: [Haskell-cafe] Current uses of Haskell in industry?
On 14 June 2012 02:00, Chris Smith wrote: > It turns out I'm filling in for a cancelled speaker at a local open > source user group, and doing a two-part talk, first on Haskell and > then Snap. For the Haskell part, I'd like a list of current places > the language is used in industry. I recall a few from Reddit stories > and messages here and other sources, but I wonder if anyone is keeping > a list. The wiki goes without saying I suppose: http://www.haskell.org/haskellwiki/Haskell_in_industry We use it for web dev here at CREATE-NET. Two public facing sites: http://confy.eai.eu/ -- For paper submission/review (like EasyChair). About 17K lines of Haskell, 20K of JS (actually some pages are Haskell compiled to JavaScript with my compiler). Couple hundred lines of Java. It was supposed to be released open source last year but you know what corporations are like. http://eudl.eu/content -- A digital archive, like IEEEXplore or ACM digital library. Not so big, about 11K lines of Haskell. Both have lots of internal-only features, IEEE/ACM/Springer communication stuff. Maybe I should add to the wiki list. Ciao! ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Current uses of Haskell in industry?
It turns out I'm filling in for a cancelled speaker at a local open source user group, and doing a two-part talk, first on Haskell and then Snap. For the Haskell part, I'd like a list of current places the language is used in industry. I recall a few from Reddit stories and messages here and other sources, but I wonder if anyone is keeping a list. -- Chris ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Perth Functional Programmers meetup group launched
Hi Todd, I am over the other side. I help organise the Brisbane Functional Programming Group. http://bfpg.org/ Although we discuss FP in general, we have a pretty strong emphasis on Haskell. Let me know how it goes or if we can help out in any way! On 14/06/12 00:46, Todd Owen wrote: > We are pleased to announce that a functional programming user group has > recently been formed in Perth, Australia. > > Being a small community, we aim to keep the group as inclusive as possible, > and welcome new members from all levels of experience and language > backgrounds. (That said, Haskellers currently account for about half our > membership, followed by F#, and then a heap of other languages). > > As this is a global mailing list, I would also like to invite our > colleagues from around Australia, and indeed anywhere in the world, to get > in touch if you are ever passing through Perth. We're always happy to share > a beer and talk about programming! > > For more information, visit: http://www.meetup.com/PerthFP/ > > > > ___ > Haskell-Cafe mailing list > Haskell-Cafe@haskell.org > http://www.haskell.org/mailman/listinfo/haskell-cafe -- Tony Morris http://tmorris.net/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Perth Functional Programmers meetup group launched
We are pleased to announce that a functional programming user group has recently been formed in Perth, Australia. Being a small community, we aim to keep the group as inclusive as possible, and welcome new members from all levels of experience and language backgrounds. (That said, Haskellers currently account for about half our membership, followed by F#, and then a heap of other languages). As this is a global mailing list, I would also like to invite our colleagues from around Australia, and indeed anywhere in the world, to get in touch if you are ever passing through Perth. We're always happy to share a beer and talk about programming! For more information, visit: http://www.meetup.com/PerthFP/ ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] Warning when attempting to install cabal-dev on the latest HP
For reference to anyone coming across this: The issue is that cabal-dev does in fact depend on the old mtl, if one checks the cabal file. (Thanks to dcoutts_ on #haskell). The suggestion I received was to use virthualenv. On Wed, Jun 13, 2012 at 9:20 AM, Edward Amsden wrote: > http://hpaste.org/69885 > > The warning in that paste occurs when I attempt > $ cabal update > $ cabal install cabal-dev > > This is curious because it wants to install a previous version of mtl. > I can't figure out why. There doesn't seem to be any dependency > between cabal-dev and mtl. According to hackage, the dependencies for > cabal-dev are: > > > cabal-dev -> (base, Cabal) > Cabal -> (base, filepath) > filepath -> (base) > base -> () > > The dependencies for mtl are (just to show no conflicts) > mtl -> (base, transformers) > transformers -> (base) > base -> () > > And there's not a versioning conflict with base. > > Why is cabal insisting on backdating mtl then? -- Edward Amsden Student Computer Science Rochester Institute of Technology www.edwardamsden.com ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] Warning when attempting to install cabal-dev on the latest HP
http://hpaste.org/69885 The warning in that paste occurs when I attempt $ cabal update $ cabal install cabal-dev This is curious because it wants to install a previous version of mtl. I can't figure out why. There doesn't seem to be any dependency between cabal-dev and mtl. According to hackage, the dependencies for cabal-dev are: cabal-dev -> (base, Cabal) Cabal -> (base, filepath) filepath -> (base) base -> () The dependencies for mtl are (just to show no conflicts) mtl -> (base, transformers) transformers -> (base) base -> () And there's not a versioning conflict with base. Why is cabal insisting on backdating mtl then? ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
Mmmmh... no, to do that you need ImpredicativeTypes (which is I believe
about to be deprecated).
You have to declare Job a data, not a type, and use
ExistentialQuantification.
2012/6/13 Ismael Figueroa Palet
> Do you want to hide the specific types of the job? Presumably to then
> define a type JobList = [Job] ?
> You can do that with the ExistentialQuantification extension.
>
> type Job = forall k a. Map k a
> type JobList = [Job]
>
> ??
> Note you can't unpack the types k a once you have hidden them. But the
> typechecker can use it to ensure some static property.
> Also you could use unsafeCoerce to do some casts, but *only if you are
> *sure* that things will go OK*.
>
>
> 2012/6/13 Magicloud Magiclouds
>
>> Hi,
>> I've forgotten this.
>> This is OK:
>> type Job k a = Map k a
>> And this is OK:
>> {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
>> type Job = forall a. forall k. Map k a
>>
>> Then how to write it like this?
>> type Job = Map k a
>> --
>> 竹密岂妨流水过
>> 山高哪阻野云飞
>>
>> And for G+, please use magiclouds#gmail.com.
>>
>> ___
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
>
>
> --
> Ismael
>
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
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Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
That doesn't require existential quantification, but it'll need Rank-2
types if you ever do anything with Job. Unfortunately, a universally
quantified Job like what you wrote (or what Magicloud seems to want) is
only inhabited by the empty Map.
An existentially quantified Job, as you might get with
data Job = forall k a. Job (Map k a)
does let you wrap up any Map containing anything in it, but unfortunately
the only thing you can do with that map afterwards is ask for "structural"
properties about it, like whether it's empty or how many elements it has in
it. You could ask to enumerate the elements in it, but you wouldn't be able
to touch any of them because you wouldn't know what their types were.
So I'm not really sure how to interpret the question. Was the goal to have
a heterogeneous Map, maybe? Or just to avoid having to type type variables
all over the place? Both of those are possible but require a bit more
sophistication with types.
-Dan
On Wed, Jun 13, 2012 at 7:32 AM, Ismael Figueroa Palet wrote:
> Do you want to hide the specific types of the job? Presumably to then
> define a type JobList = [Job] ?
> You can do that with the ExistentialQuantification extension.
>
> type Job = forall k a. Map k a
> type JobList = [Job]
>
> ??
> Note you can't unpack the types k a once you have hidden them. But the
> typechecker can use it to ensure some static property.
> Also you could use unsafeCoerce to do some casts, but *only if you are
> *sure* that things will go OK*.
>
>
> 2012/6/13 Magicloud Magiclouds
>
>> Hi,
>> I've forgotten this.
>> This is OK:
>> type Job k a = Map k a
>> And this is OK:
>> {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
>> type Job = forall a. forall k. Map k a
>>
>> Then how to write it like this?
>> type Job = Map k a
>> --
>> 竹密岂妨流水过
>> 山高哪阻野云飞
>>
>> And for G+, please use magiclouds#gmail.com.
>>
>> ___
>> Haskell-Cafe mailing list
>> Haskell-Cafe@haskell.org
>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>
>
>
>
> --
> Ismael
>
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
>
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Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
Do you want to hide the specific types of the job? Presumably to then
define a type JobList = [Job] ?
You can do that with the ExistentialQuantification extension.
type Job = forall k a. Map k a
type JobList = [Job]
??
Note you can't unpack the types k a once you have hidden them. But the
typechecker can use it to ensure some static property.
Also you could use unsafeCoerce to do some casts, but *only if you are
*sure* that things will go OK*.
2012/6/13 Magicloud Magiclouds
> Hi,
> I've forgotten this.
> This is OK:
> type Job k a = Map k a
> And this is OK:
> {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
> type Job = forall a. forall k. Map k a
>
> Then how to write it like this?
> type Job = Map k a
> --
> 竹密岂妨流水过
> 山高哪阻野云飞
>
> And for G+, please use magiclouds#gmail.com.
>
> ___
> Haskell-Cafe mailing list
> Haskell-Cafe@haskell.org
> http://www.haskell.org/mailman/listinfo/haskell-cafe
>
--
Ismael
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Re: [Haskell-cafe] What extension do I need to write "type Job = Map k a"?
On 13 June 2012 19:59, Magicloud Magiclouds
wrote:
> Hi,
> I've forgotten this.
> This is OK:
> type Job k a = Map k a
> And this is OK:
> {-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
> type Job = forall a. forall k. Map k a
>
> Then how to write it like this?
> type Job = Map k a
Does that even make sense? What are the types of `k' and `a' in Job?
--
Ivan Lazar Miljenovic
ivan.miljeno...@gmail.com
http://IvanMiljenovic.wordpress.com
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[Haskell-cafe] What extension do I need to write "type Job = Map k a"?
Hi,
I've forgotten this.
This is OK:
type Job k a = Map k a
And this is OK:
{-# LANGUAGE RankNTypes #-} -- or LiberalTypeSynonyms?
type Job = forall a. forall k. Map k a
Then how to write it like this?
type Job = Map k a
--
竹密岂妨流水过
山高哪阻野云飞
And for G+, please use magiclouds#gmail.com.
___
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Re: [Haskell-cafe] Performance with do notation, mwc-random and unboxed vector
On 12 Jun 2012, at 12:52, Dmitry Dzhus wrote: > 12.06.2012, 01:08, "Roman Leshchinskiy" : > >> perhaps the state hack is getting in the way. > > I don't quite understand the internals of this yet, but `-fno-state-hack` > leads to great performance in both cases! > How safe is that? It doesn't change the semantics of your program but it can make it significantly slower (or faster, as in this case). The various state hack related tickets on trac might give you an idea of what is happening here. We really need some proper arity analysis! Roman ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
[Haskell-cafe] RawFilePath vs System.FilePath
Hello, After releaseing new Haskell Platform, many people can now use RawFilePath (e.g. ByteString) for System.*. However, there is no System.FilePath.ByteString which manipulates RawFilePath. How do you guys manipulate RawFilePath as file path? Is there a plan to implement System.FilePath.ByteString? # I know the system-filepath package. But I would like to know # answers to the questions above. Regards, --Kazu ___ Haskell-Cafe mailing list Haskell-Cafe@haskell.org http://www.haskell.org/mailman/listinfo/haskell-cafe
