RFC: Remove -fwarn-unticked-promoted-constructors from -Wall

Jan Stolarek jan.stolarek at p.lodz.pl
Thu Dec 18 17:26:51 UTC 2014

We recently got a new warning -fwarn-unticked-promoted-constructors (see #9778 and D534). This 
warning is enabled with -Wall but I think that this is not a good idea. I strongly propose to 
remove it with -Wall.

1. I feel that ticks add unnecessary noise:

prDictOfPReprInstTyCon :: Type -> CoAxiom 'Unbranched -> [Type] -> VM CoreExpr

To me it feels awkward to have Unbranched with a tick but CoreExpr without a tick (both are types 
after all). Moreover, ticks also trip many syntax highlighters, which further degrades code 

2. I've been refactoring some of GHC code to use promoted types instead of empty data types (see 
CoAxiom.BranchList). This would have been a fairly local change, except that I have to add ticks 
in every place that mentiones promoted types. That's a Royal Pain and a "good" example how this 
warning can get in people's way.


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