Changes in src/Parser/lex.ll [daf9671:ba2356b]

File:

• src/Parser/lex.ll (modified) (2 diffs)

src/Parser/lex.ll

@@ -10 +10 @@
  * Created On       : Sat Sep 22 08:58:10 2001
  * Last Modified By : Peter A. Buhr
- * Last Modified On : Mon May 22 07:46:30 2017
- * Update Count     : 525
+ * Last Modified On : Thu May 18 09:03:49 2017
+ * Update Count     : 513
  */
 
@@ -377 +377 @@
 "?"{op_binary_over}"?"  { IDENTIFIER_RETURN(); }                // binary
         /*
-          This rule handles ambiguous cases with operator identifiers, e.g., "int *?*?()", where the string "*?*?"  can be
-          lexed as "*?"/"*?" or "*"/"?*?". Since it is common practise to put a unary operator juxtaposed to an identifier,
-          e.g., "*i", users will be annoyed if they cannot do this with respect to operator identifiers. Therefore, there is
-          a lexical look-ahead for the second case, with backtracking to return the leading unary operator and then
-          reparsing the trailing operator identifier.  Otherwise a space is needed between the unary operator and operator
-          identifier to disambiguate this common case.
-
-          A similar issue occurs with the dereference, *?(...), and routine-call, ?()(...) identifiers.  The ambiguity
-          occurs when the deference operator has no parameters, *?() and *?()(...), requiring arbitrary whitespace
-          look-ahead for the routine-call parameter-list to disambiguate.  However, the dereference operator must have a
-          parameter/argument to dereference *?(...).  Hence, always interpreting the string *?() as * ?() does not preclude
-          any meaningful program.
-
-          The remaining cases are with the increment/decrement operators and conditional expression:
-
-          i++? ...(...);
-          i?++ ...(...);
-
-          requiring arbitrary whitespace look-ahead for the operator parameter-list, even though that interpretation is an
-      incorrect expression (juxtaposed identifiers).  Therefore, it is necessary to disambiguate these cases with a
-      space:
-
-          i++ ? i : 0;
-          i? ++i : 0;
+          This rule handles ambiguous cases with operator identifiers, e.g., "int *?*?()", where the string "*?*?"
+          can be lexed as "*"/"?*?" or "*?"/"*?". Since it is common practise to put a unary operator juxtaposed
+          to an identifier, e.g., "*i", users will be annoyed if they cannot do this with respect to operator
+          identifiers. Even with this special hack, there are 5 general cases that cannot be handled. The first
+          case is for the function-call identifier "?()":
+
+          int * ?()();  // declaration: space required after '*'
+          * ?()();      // expression: space required after '*'
+
+          Without the space, the string "*?()" is ambiguous without N character look ahead; it requires scanning
+          ahead to determine if there is a '(', which is the start of an argument/parameter list.
+
+          The 4 remaining cases occur in expressions:
+
+          i++?i:0;              // space required before '?'
+          i--?i:0;              // space required before '?'
+          i?++i:0;              // space required after '?'
+          i?--i:0;              // space required after '?'
+
+          In the first two cases, the string "i++?" is ambiguous, where this string can be lexed as "i"/"++?" or
+          "i++"/"?"; it requires scanning ahead to determine if there is a '(', which is the start of an argument
+          list.  In the second two cases, the string "?++x" is ambiguous, where this string can be lexed as
+          "?++"/"x" or "?"/"++x"; it requires scanning ahead to determine if there is a '(', which is the start of
+          an argument list.
         */
-{op_unary}"?"({op_unary_pre_post}|"()"|"[?]"|{op_binary_over}"?") {
+{op_unary}"?"({op_unary_pre_post}|"[?]"|{op_binary_over}"?") {
         // 1 or 2 character unary operator ?
         int i = yytext[1] == '?' ? 1 : 2;