-dsExpr (HsCase discrim matches) = do
- core_discrim <- dsLExpr discrim
- ([discrim_var], matching_code) <- matchWrapper CaseAlt matches
- return (scrungleMatch discrim_var core_discrim matching_code)
+dsExpr (HsCase discrim matches@(MatchGroup _ rhs_ty))
+ | isEmptyMatchGroup matches -- A Core 'case' is always non-empty
+ = -- So desugar empty HsCase to error call
+ mkErrorAppDs pAT_ERROR_ID (funResultTy rhs_ty) "case"
+
+ | otherwise
+ = do { core_discrim <- dsLExpr discrim
+ ; ([discrim_var], matching_code) <- matchWrapper CaseAlt matches
+ ; return (scrungleMatch discrim_var core_discrim matching_code) }