[parser] Refactor parser and preparser traits

src/parsing/parser-base.h

Index: src/parsing/parser-base.h
diff --git a/src/parsing/parser-base.h b/src/parsing/parser-base.h
index 2f9393517036fbb8ad456cb65ff1ffdcd17305fb..9b78ee9a2805eaa5bea7d8c951d04915a9e0db19 100644
--- a/src/parsing/parser-base.h
+++ b/src/parsing/parser-base.h
@@ -126,19 +126,15 @@ struct FormalParametersBase {
 // thus it must never be used where only a single statement
 // is correct (e.g. an if statement branch w/o braces)!
 
-#define CHECK_OK  ok);                      \
-  if (!*ok) return this->EmptyExpression(); \
-  ((void)0
-#define DUMMY )  // to make indentation work
-#undef DUMMY
-
-// Used in functions where the return type is not ExpressionT.
 #define CHECK_OK_CUSTOM(x) ok); \
   if (!*ok) return this->x();   \
   ((void)0
 #define DUMMY )  // to make indentation work
 #undef DUMMY
 
+// Used in functions where the return type is ExpressionT.
+#define CHECK_OK CHECK_OK_CUSTOM(EmptyExpression)
+
 
 // Common base class shared between parser and pre-parser. Traits encapsulate
 // the differences between Parser and PreParser: