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

Roman Cheplyaka roma at
Fri Feb 5 07:22:54 UTC 2016

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/.


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