duplicateDefinitions :: ErrorExtractor v loc (NonEmpty (v, [loc]))
duplicateDefinitions = cause >>= \case
  C.DuplicateDefinitions vs -> pure vs
  _                         -> mzero
duplicateDefinitions :: ErrorExtractor v loc (NonEmpty (v, [loc]))
duplicateDefinitions = cause >>= \case
  C.DuplicateDefinitions vs -> pure vs
  _                         -> mzero
duplicateDefinitions = cause >>= \case
  C.DuplicateDefinitions vs -> pure vs
  _                         -> mzero