Changeset daf9671 for src/Parser/lex.ll

Timestamp:

May 24, 2017, 5:36:41 PM (7 years ago)

Author:

Peter A. Buhr <pabuhr@…>

Branches:

ADT, aaron-thesis, arm-eh, ast-experimental, cleanup-dtors, deferred_resn, demangler, enum, forall-pointer-decay, jacob/cs343-translation, jenkins-sandbox, master, new-ast, new-ast-unique-expr, new-env, no_list, persistent-indexer, pthread-emulation, qualifiedEnum, resolv-new, with_gc

Children:

3c0ec68

Parents:

678765c

Message:

change lexing of multiply operator identifier

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 : Thu May 18 09:03:49 2017
- * Update Count     : 513
+ * Last Modified On : Mon May 22 07:46:30 2017
+ * Update Count     : 525
  */
 
@@ -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. 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.
+          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;
         */
-{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;