New type of ($) operator in GHC 8.0 is problematic

Manuel M T Chakravarty chak at
Sat Feb 6 10:57:50 UTC 2016

That makes a lot of sense to me.


> Roman Cheplyaka <roma at>:
> On 02/05/2016 01:31 AM, Edward Z. Yang wrote:
>> I'm not really sure how you would change the type of 'id' based on
>> a language pragma.
>> How do people feel about a cosmetic fix, where we introduce a new
>> pragma, {-# LANGUAGE ShowLevity #-} which controls the display of levity
>> arguments/TYPE.  It's off by default but gets turned on by some
>> extensions like MagicHash (i.e. we only show levity if you have
>> enabled extensions where the distinction matters).
> Yes, I am surprised this isn't the way it's been done. The levity
> arguments should totally be hidden unless requested explicitly.
> I'd only expect this to be a ghc flag (-fshow-levity), not a language
> pragma, since it should only affect the way types are /shown/.
> Roman
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