[Haskell-cafe] What extension do I need to write "type Job = Map k a"?

[Yves Parès]

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 <ifigueroap at gmail.com>

> 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 <magicloud.magiclouds at gmail.com>
>
>> 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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>
>
>
> --
> Ismael
>
>
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