Sorry, the last 'a' of line 22 is 'b'.
On Thu, Jun 14, 2012 at 3:19 PM, Magicloud Magiclouds
<magicloud.magiclo...@gmail.com> wrote:
> OK. I am totally confused here. Why "Couldn't match expected type
> `Jobs k e a' with actual type `M.Map k0 b0'"....
>
> 9|data JobInfo a e = (Exception e) =>
> 10| JobInfo { jobId :: ThreadId
> 11| , result :: MVar (Either e a) }
> 12|
> 13|type Jobs k e a = (Ord k, Exception e) =>
> 14| M.Map k (JobInfo e a)
> 15|
> 16|type JobArgs k a = (Ord k) =>
> 17| M.Map k a
> 21|
> 22|start :: (Ord k, Exception e) => JobArgs k a -> (a -> IO b) -> IO
> (Jobs k e a)
> 23|start args worker = do
> 24| arg <- newEmptyMVar
> 25| Map.mapM (\a -> do
> 26| putMVar arg a
> 27| result <- newEmptyMVar
> 28| tId <- forkIO $ do
> 29| arg_ <- takeMVar arg
> 30| result_ <- try $ worker arg_
> 31| putMVar result result_
> 32| return $ JobInfo tId result
> 33| ) args
>
> On Thu, Jun 14, 2012 at 1:24 PM, Magicloud Magiclouds
> <magicloud.magiclo...@gmail.com> wrote:
>> I think I need to think this through....
>>
>> On Thu, Jun 14, 2012 at 12:28 PM, Ivan Lazar Miljenovic
>> <ivan.miljeno...@gmail.com> wrote:
>>> On 14 June 2012 14:20, Magicloud Magiclouds
>>> <magicloud.magiclo...@gmail.com> 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 <a...@len.me> 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 <pumpkin...@gmail.com
>>>>>> (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<ifiguer...@gmail.com (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 <magicloud.magiclo...@gmail.com
>>>>>> (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/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.
>>>>
>>>> _______________________________________________
>>>> Haskell-Cafe mailing list
>>>> Haskell-Cafe@haskell.org
>>>> http://www.haskell.org/mailman/listinfo/haskell-cafe
>>>
>>>
>>>
>>> --
>>> Ivan Lazar Miljenovic
>>> ivan.miljeno...@gmail.com
>>> http://IvanMiljenovic.wordpress.com
>>
>>
>>
>> --
>> 竹密岂妨流水过
>> 山高哪阻野云飞
>>
>> And for G+, please use magiclouds#gmail.com.
>
>
>
> --
> 竹密岂妨流水过
> 山高哪阻野云飞
>
> And for G+, please use magiclouds#gmail.com.
--
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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