RFC: Remove -fwarn-unticked-promoted-constructors from -Wall
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. Rationale: 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 readability. 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. Janek
For what it's worth, I don't have a strong feeling either way here. Arguments in favor of keeping -fwarn-unticked-promoted-constructors in -Wall: 1. It's weird having GHC look in one namespace (types) and then look in another (terms) only when the first one fails. In other scenarios, ambiguity is an error. 2. If I have my way (https://ghc.haskell.org/trac/ghc/wiki/DependentHaskell), this problem will only get worse. 3. Whenever presenting code involving promoted constructors, I put the tick marks in everywhere, as I think it makes the code easier to understand. 4. There is an easy workaround:
type Unbranched = 'Unbranched
Arguments against keeping -fwarn-unticked-promoted-constructors in -Wall:
1,2. As Janek.
3. If you've made a mistake around using a type where a promoted data constructor is meant, or vice versa, it's very likely you have an error in your code. This will lead to a perhaps-obscure, perhaps-confusing error message instead of a nice clean warning, which is suppressed when there are errors.
Adding this all up, I can't really decide which is best.
Richard
On Dec 18, 2014, at 12:26 PM, Jan Stolarek
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.
Rationale: 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 readability.
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.
Janek
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participants (2)
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Jan Stolarek -
Richard Eisenberg