unknownSymbol :: ErrorExtractor v loc (loc, v)
unknownSymbol = cause >>= \case
  C.UnknownSymbol loc v -> pure (loc, v)
  _                     -> mzero
unknownSymbol :: ErrorExtractor v loc (loc, v)
unknownSymbol = cause >>= \case
  C.UnknownSymbol loc v -> pure (loc, v)
  _                     -> mzero
unknownSymbol = cause >>= \case
  C.UnknownSymbol loc v -> pure (loc, v)
  _                     -> mzero