-- NB: The success of this clause depends on the typechecker not
-- wrapping the 'otherwise' in empty HsTyApp or HsWrap constructors
-- If it does, you'll get bogus overlap warnings
-matchGuards (ExprStmt (L _ (HsVar v)) _ _ : stmts) ctx rhs rhs_ty
- | v `hasKey` otherwiseIdKey
- || v `hasKey` getUnique trueDataConId
- -- trueDataConId doesn't have the same unique as trueDataCon
- = matchGuards stmts ctx rhs rhs_ty
-
+matchGuards (ExprStmt e _ _ : stmts) ctx rhs rhs_ty
+ | Just addTicks <- isTrueLHsExpr e
+ = matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
+ returnDs (adjustMatchResultDs addTicks match_result)
matchGuards (ExprStmt expr _ _ : stmts) ctx rhs rhs_ty
= matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
dsLExpr expr `thenDs` \ pred_expr ->
= matchGuards stmts ctx rhs rhs_ty `thenDs` \ match_result ->
dsLExpr bind_rhs `thenDs` \ core_rhs ->
matchSinglePat core_rhs 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 returnDs
+ -- trueDataConId doesn't have the same unique as trueDataCon
+isTrueLHsExpr (L loc (HsTick ix frees e))
+ | Just ticks <- isTrueLHsExpr e = Just (\ e1 ->
+ ticks e1 `thenDs` \ e2 ->
+ mkTickBox ix frees e2)
+ -- This encodes that the result is constant True for Hpc tick purposes;
+ -- which is specifically what isTrueLHsExpr is trying to find out.
+isTrueLHsExpr (L loc (HsBinTick ixT _ e))
+ | Just ticks <- isTrueLHsExpr e = Just (\ e1 ->
+ ticks e1 `thenDs` \ e2 ->
+ mkTickBox ixT [] e2)
+isTrueLHsExpr (L _ (HsPar e)) = isTrueLHsExpr e
+isTrueLHsExpr other = Nothing
\end{code}
Should {\em fail} if @e@ returns @D@