changes_summary.txt

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            rule : (guard)? && <<p>>? expr
                 | next_alternative
                 ;

      The new style of context guarded predicate is equivalent to:

            rule : <<guard==true && pred>>? expr
                 | next_alternative
                 ;

      It generates code which resembles:

            if (lookahead(expr) && guard && pred) {
                expr();
            } else ...

      Both forms of guarded predicates severely restrict the form of
      the context guard: it can contain no rule references, no
      (...)*, no (...)+, and no {...}.  It may contain token and
      token class references, and alternation ("|").

      Addition for 1.33MR11: in the token expression all tokens must
      be at the same height of the token tree:

            (A ( B | C))? && ...            is ok (all height 2)
            (A ( B |  ))? && ...            is not ok (some 1, some 2)
            (A B C D | E F G H)? && ...     is ok (all height 4)
            (A B C D | E )? && ...          is not ok (some 4, some 1)

      This restriction is required in order to properly compute the lookahead
      set for expressions like:

            rule1 : (A B C)? && <<pred>>? rule2 ;
            rule2 : (A|X) (B|Y) (C|Z);

      This addition was suggested by Rienier van den Born ([e-mail])

#109. (Changed in 1.33MR10) improved trace information

      The quality of the trace information provided by the "-gd"
      switch has been improved significantly.  Here is an example
      of the output from a test program.  It shows the rule name,
      the first token of lookahead, the call depth, and the guess
      status:

        exit rule gusxx {"?"} depth 2
        enter rule gusxx {"?"} depth 2
        enter rule gus1 {"o"} depth 3 guessing
        guess done - returning to rule gus1 {"o"} at depth 3
                    (guess mode continues - an enclosing guess is still active)
        guess done - returning to rule gus1 {"Z"} at depth 3
                    (guess mode continues - an enclosing guess is still active)
        exit rule gus1 {"Z"} depth 3 guessing
        guess done - returning to rule gusxx {"o"} at depth 2 (guess mode ends)
        enter rule gus1 {"o"} depth 3
        guess done - returning to rule gus1 {"o"} at depth 3 (guess mode ends)
        guess done - returning to rule gus1 {"Z"} at depth 3 (guess mode ends)
        exit rule gus1 {"Z"} depth 3
        line 1: syntax error at "Z" missing SC
            ...

      Rule trace reporting is controlled by the value of the integer
      [zz]traceOptionValue:  when it is positive tracing is enabled,
      otherwise it is disabled.  Tracing during guess mode is controlled
      by the value of the integer [zz]traceGuessOptionValue.  When
      it is positive AND [zz]traceOptionValue is positive rule trace
      is reported in guess mode.

      The values of [zz]traceOptionValue and [zz]traceGuessOptionValue
      can be adjusted by subroutine calls listed below.

      Depending on the presence or absence of the antlr -gd switch
      the variable [zz]traceOptionValueDefault is set to 0 or 1.  When
      the parser is initialized or [zz]traceReset() is called the
      value of [zz]traceOptionValueDefault is copied to [zz]traceOptionValue.
      The value of [zz]traceGuessOptionValue is always initialzed to 1,
      but, as noted earlier, nothing will be reported unless
      [zz]traceOptionValue is also positive.

      When the parser state is saved/restored the value of the trace
      variables are also saved/restored.  If a restore causes a change in
      reporting behavior from on to off or vice versa this will be reported.

      When the -gd option is selected, the macro "#define zzTRACE_RULES"
      is added to appropriate output files.

        C++ mode
        --------
        int     traceOption(int delta)
        int     traceGuessOption(int delta)
        void    traceReset()
        int     traceOptionValueDefault

        C mode
        --------
        int     zzTraceOption(int delta)
        int     zzTraceGuessOption(int delta)
        void    zzTraceReset()
        int     zzTraceOptionValueDefault

      The argument "delta" is added to the traceOptionValue.  To
      turn on trace when inside a particular rule one:

        rule : <<traceOption(+1);>>
               (
                rest-of-rule
               )
               <<traceOption(-1);>>
       ;  /* fail clause */ <<traceOption(-1);>>

      One can use the same idea to turn *off* tracing within a
      rule by using a delta of (-1).

      An improvement in the rule trace was suggested by Sramji
      Ramanathan ([e-mail]).

#108. A Note on Deallocation of Variables Allocated in Guess Mode

                            NOTE
        ------------------------------------------------------
        This mechanism only works for heap allocated variables
        ------------------------------------------------------

      The rewrite of the trace provides the machinery necessary
      to properly free variables or undo actions following a
      failed guess.

      The macro zzUSER_GUESS_HOOK(guessSeq,zzrv) is expanded
      as part of the zzGUESS macro.  When a guess is opened
      the value of zzrv is 0.  When a longjmp() is executed to
      undo the guess, the value of zzrv will be 1.

      The macro zzUSER_GUESS_DONE_HOOK(guessSeq) is expanded
      as part of the zzGUESS_DONE macro.  This is executed
      whether the guess succeeds or fails as part of closing
      the guess.

      The guessSeq is a sequence number which is assigned to each
      guess and is incremented by 1 for each guess which becomes
      active.  It is needed by the user to associate the start of
      a guess with the failure and/or completion (closing) of a
      guess.

      Guesses are nested.  They must be closed in the reverse
      of the order that they are opened.

      In order to free memory used by a variable during a guess
      a user must write a routine which can be called to
      register the variable along with the current guess sequence
      number provided by the zzUSER_GUESS_HOOK macro. If the guess
      fails, all variables tagged with the corresponding guess
      sequence number should be released.  This is ugly, but
      it would require a major rewrite of antlr 1.33 to use
      some mechanism other than setjmp()/longjmp().

      The order of calls for a *successful* guess would be:

        zzUSER_GUESS_HOOK(guessSeq,0);
        zzUSER_GUESS_DONE_HOOK(guessSeq);

      The order of calls for a *failed* guess would be:

        zzUSER_GUESS_HOOK(guessSeq,0);
        zzUSER_GUESS_HOOK(guessSeq,1);
        zzUSER_GUESS_DONE_HOOK(guessSeq);

      The default definitions of these macros are empty strings.

      Here is an example in C++ mode.  The zzUSER_GUESS_HOOK and
      zzUSER_GUESS_DONE_HOOK macros and myGuessHook() routine
      can be used without change in both C and C++ versions.

      ----------------------------------------------------------------------
        <<

        #include "AToken.h"

        typedef ANTLRCommonToken ANTLRToken;

        #include "DLGLexer.h"

        int main() {

          {
            DLGFileInput     in(stdin);
            DLGLexer         lexer(&in,2000);
            ANTLRTokenBuffer pipe(&lexer,1);
            ANTLRCommonToken aToken;
            P                parser(&pipe);

            lexer.setToken(&aToken);
            parser.init();
            parser.start();
          };

          fclose(stdin);
          fclose(stdout);
          return 0;
        }

        >>

        <<
        char *s=NULL;

        #undef zzUSER_GUESS_HOOK
        #define zzUSER_GUESS_HOOK(guessSeq,zzrv) myGuessHook(guessSeq,zzrv);
        #undef zzUSER_GUESS_DONE_HOOK
        #define zzUSER_GUESS_DONE_HOOK(guessSeq)   myGuessHook(guessSeq,2);

        void myGuessHook(int guessSeq,int zzrv) {
          if (zzrv == 0) {
            fprintf(stderr,"User hook: starting guess #%d\n",guessSeq);
          } else if (zzrv == 1) {
            free (s);
            s=NULL;
            fprintf(stderr,"User hook: failed guess #%d\n",guessSeq);
          } else if (zzrv == 2) {
            free (s);
            s=NULL;
            fprintf(stderr,"User hook: ending guess #%d\n",guessSeq);
          };
        }

        >>

        #token A    "a"
        #token      "[\t \ \n]"     <<skip();>>

        class P {

        start : (top)+
              ;

        top   : (which) ?   <<fprintf(stderr,"%s is a which\n",s); free(s); s=NULL; >>
              | other       <<fprintf(stderr,"%s is an other\n",s); free(s); s=NULL; >>
              ; <<if (s != NULL) free(s); s=NULL; >>

        which : which2
              ;

        which2 : which3
              ;
        which3
              : (label)?         <<fprintf(stderr,"%s is a label\n",s);>>
              | (global)?        <<fprintf(stderr,"%s is a global\n",s);>>
              | (exclamation)?   <<fprintf(stderr,"%s is an exclamation\n",s);>>
              ;

        label :       <<s=strdup(LT(1)->getText());>> A ":" ;

        global :      <<s=strdup(LT(1)->getText());>> A "::" ;

        exclamation : <<s=strdup(LT(1)->getText());>> A "!" ;

        other :       <<s=strdup(LT(1)->getText());>> "other" ;

        }
      ----------------------------------------------------------------------

      This is a silly example, but illustrates the idea.  For the input
      "a ::" with tracing enabled the output begins:

      ----------------------------------------------------------------------
        enter rule "start" depth 1
        enter rule "top" depth 2
        User hook: starting guess #1
        enter rule "which" depth 3 guessing
        enter rule "which2" depth 4 guessing
        enter rule "which3" depth 5 guessing
        User hook: starting guess #2
        enter rule "label" depth 6 guessing
        guess failed
        User hook: failed guess #2
        guess done - returning to rule "which3" at depth 5 (guess mode continues
                                                 - an enclosing guess is still active)
        User hook: ending guess #2
        User hook: starting guess #3
        enter rule "global" depth 6 guessing
        exit rule "global" depth 6 guessing
        guess done - returning to rule "which3" at depth 5 (guess mode continues
                                                 - an enclosing guess is still active)
        User hook: ending guess #3
        enter rule "global" depth 6 guessing
        exit rule "global" depth 6 guessing
        exit rule "which3" depth 5 guessing
        exit rule "which2" depth 4 guessing
        exit rule "which" depth 3 guessing
        guess done - returning to rule "top" at depth 2 (guess mode ends)
        User hook: ending guess #1
        enter rule "which" depth 3
        .....
      ----------------------------------------------------------------------

      Remember:

        (a) Only init-actions are executed during guess mode.
        (b) A rule can be invoked multiple times during guess mode.
        (c) If the guess succeeds the rule will be called once more
              without guess mode so that normal actions will be executed.
            This means that the init-action might need to distinguish
              between guess mode and non-guess mode using the variable
              [zz]guessing.

#101. (Changed in 1.33MR10) antlr -info command line switch

        -info

            p   - extra predicate information in generated file

            t   - information about tnode use:
                    at the end of each rule in generated file
                    summary on stderr at end of program

            m   - monitor progress
                    prints name of each rule as it is started
                    flushes