[Haskell-cafe] New type of ($) operator in GHC 8.0 is problematic

[Artyom]

I agree, it’s a bit too heavy. In fact, since most users probably won’t 
ever ever ever need that type, let’s only impose it on those who 
explicitly agree to see it:

| > :t ($) -- Note: the actual type is slightly more generic; set 
-fshow-levity -- or use :t# instead of :t to see the fully generic form. 
($) :: (a -> b) -> a -> b |

On 02/06/2016 03:06 AM, Mihai Maruseac wrote:

> On Fri, Feb 5, 2016 at 6:22 PM, Artyom <yom at artyom.me> wrote:
>> Why not just make GHCi output a comment whenever the type involves levity?
>>
>>> :t ($)
>> -- Note: the actual type is more generic:
>> --
>> --     ($) :: forall (w :: GHC.Types.Levity) a (b :: TYPE w).  (a -> b) -> a
>> -> b
>> --
>> -- For the absolute majority of purposes the simpler type is correct.
>> -- See GHC Guide chapter X point Y to learn more about this.
>>
>> ($) :: (a -> b) -> a -> b
>>
> Wouldn't this look like a scary error to some users? Though, users can
> get accustomed to this and this solution seems to be the best of both
> worlds.
>
>
>
​
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