-matchGuards (BindStmt pat bind_rhs _ _ : stmts) ctx rhs rhs_ty
- = matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
- dsLExpr bind_rhs `thenDs` \ core_rhs ->
- matchSinglePat core_rhs ctx pat rhs_ty match_result
+matchGuards (BindStmt pat bind_rhs _ _ : stmts) ctx rhs rhs_ty = do
+ match_result <- matchGuards stmts ctx rhs rhs_ty
+ core_rhs <- dsLExpr bind_rhs
+ matchSinglePat core_rhs (StmtCtxt ctx) pat rhs_ty match_result
+
+isTrueLHsExpr :: LHsExpr Id -> Maybe (CoreExpr -> DsM CoreExpr)
+
+-- Returns Just {..} if we're sure that the expression is True
+-- I.e. * 'True' datacon
+-- * 'otherwise' Id
+-- * Trivial wappings of these
+-- The arguments to Just are any HsTicks that we have found,
+-- because we still want to tick then, even it they are aways evaluted.
+isTrueLHsExpr (L _ (HsVar v)) | v `hasKey` otherwiseIdKey
+ || v `hasKey` getUnique trueDataConId
+ = Just return
+ -- trueDataConId doesn't have the same unique as trueDataCon
+isTrueLHsExpr (L _ (HsTick ix frees e))
+ | Just ticks <- isTrueLHsExpr e = Just (\x -> ticks x >>= mkTickBox ix frees)
+ -- This encodes that the result is constant True for Hpc tick purposes;
+ -- which is specifically what isTrueLHsExpr is trying to find out.
+isTrueLHsExpr (L _ (HsBinTick ixT _ e))
+ | Just ticks <- isTrueLHsExpr e = Just (\x -> ticks x >>= mkTickBox ixT [])
+isTrueLHsExpr (L _ (HsPar e)) = isTrueLHsExpr e
+isTrueLHsExpr _ = Nothing