Improve unification error when it fails #9
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shulhi
commented
Dec 23, 2022
shulhi
commented
- Previously, this returns an empty list when no two types match.
- Also, this handles returning error with dummy location when carried type errors are empty. Otherwise, when the carried type errors are empty, this function just returns an empty list instead of unification error.
| @@ -381,7 +381,7 @@ inferTypeReps allTypeClasses (ForallTC tvs tyCls (ImplType _impl ty)) inputTys o | |||
| Left errs -> Left errs | |||
| Right subst -> | |||
| let tyClsSubst = Set.map (apply subst) tyCls | |||
| in case find (\(TypeClass nm _) -> nm == "rep") $ Set.toList tyClsSubst of | |||
| in case List.find (\(TypeClass nm _) -> nm == "rep") $ Set.toList tyClsSubst of | |||
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hmm not sure why i wasn't just using set find here?? probably not terribly important tho
| | List.null err = | ||
| let pos = initialPos "" | ||
| loc = (pos, pos) | ||
| in throwError [UnificationFail Set.empty (TTuple ts1) (TTuple ts2) loc] | ||
| | otherwise = throwError [UnificationFail (getTypeClassFromErrs err) (TTuple ts1) (TTuple ts2) loc | loc <- (getLocFromErrs err)] |
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Looking at this code, the error throwing doesn't really make sense. My original design is definitely wonky here. The idea behind throwing a list was to link several places in code which generate a contradiction. e.g. somewhere we assign a variable the value bool and elsewhere we try to add a number to it. the error should point to those two places in the code as a contradiction. However, I'm not sure this ever properly worked as intended. It seems we always just throw a singleton error anyway.
To get proper error location, we should probably track location for types we are unifying and then add those to the error when throwing, instead of adding a dummy pos. This will require a bit of a re-engineering tho.
