helpful comment

source/constants.h

@@ -73,8 +73,12 @@
 
 #define STMTMAX 10000				   /* maximum source statement length */
 
-#define STR2(x)			   #x
-#define STRINGIZE(x)	   STR2(x)
+/* NOTE: _STRINGIZE ensures that if the argument is a macro,
+ *        its expanded before stringinization
+ */
+#define _STRINGIZE(x) #x
+#define STRINGIZE(x)  _STRINGIZE(x)
+
 #define PATLEN_STR         STRINGIZE(PATLEN)
 #define PATHLEN_STR        STRINGIZE(PATHLEN)
 #define NUMLEN_STR         STRINGIZE(NUMLEN)
@@ -101,6 +105,7 @@ enum {
 #else
 # define READ 4
 #endif
+
 #ifdef W_OK
 # define WRITE W_OK
 #else