dsExpr (HsCoreAnn fs expr)
= Note (CoreNote $ unpackFS fs) <$> dsLExpr expr
-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) }
-- Pepe: The binds are in scope in the body but NOT in the binding group
-- This is to avoid silliness in breakpoints
dsExpr (ExplicitList elt_ty xs)
= dsExplicitList elt_ty xs
--- we create a list from the array elements and convert them into a list using
--- `PrelPArr.toP'
---
--- * the main disadvantage to this scheme is that `toP' traverses the list
--- twice: once to determine the length and a second time to put to elements
--- into the array; this inefficiency could be avoided by exposing some of
--- the innards of `PrelPArr' to the compiler (ie, have a `PrelPArrBase') so
--- that we can exploit the fact that we already know the length of the array
--- here at compile time
+-- We desugar [:x1, ..., xn:] as
+-- singletonP x1 +:+ ... +:+ singletonP xn
--
+dsExpr (ExplicitPArr ty []) = do
+ emptyP <- dsLookupGlobalId emptyPName
+ return (Var emptyP `App` Type ty)
dsExpr (ExplicitPArr ty xs) = do
- toP <- dsLookupGlobalId toPName
- coreList <- dsExpr (ExplicitList ty xs)
- return (mkApps (Var toP) [Type ty, coreList])
+ singletonP <- dsLookupGlobalId singletonPName
+ appP <- dsLookupGlobalId appPName
+ xs' <- mapM dsLExpr xs
+ return . foldr1 (binary appP) $ map (unary singletonP) xs'
+ where
+ unary fn x = mkApps (Var fn) [Type ty, x]
+ binary fn x y = mkApps (Var fn) [Type ty, x, y]
dsExpr (ExplicitTuple expr_list boxity) = do
core_exprs <- mapM dsLExpr expr_list
dsExplicitList elt_ty xs = do
dflags <- getDOptsDs
xs' <- mapM dsLExpr xs
- if not (dopt Opt_RewriteRules dflags)
+ if not (dopt Opt_EnableRewriteRules dflags)
then return $ mkListExpr elt_ty xs'
else mkBuildExpr elt_ty (mkSplitExplicitList (thisPackage dflags) xs')
where