changes_summary.txt

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                       CHANGES_SUMMARY.TXT

        A QUICK overview of changes from 1.33 in reverse order

  A summary of additions rather than bug fixes and minor code changes.

          Numbers refer to items in CHANGES_FROM_133*.TXT
             which may contain additional information.

                          DISCLAIMER

 The software and these notes are provided "as is".  They may include
 typographical or technical errors and their authors disclaims all
 liability of any kind or nature for damages due to error, fault,
 defect, or deficiency regardless of cause.  All warranties of any
 kind, either express or implied, including, but not limited to, the
 implied  warranties of merchantability and fitness for a particular
 purpose are disclaimed.

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#258. You can specify a user-defined base class for your parser

    The base class must constructor must have a signature similar to
    that of ANTLRParser.

#253. Generation of block preamble (-preamble and -preamble_first)

    The antlr option -preamble causes antlr to insert the code
    BLOCK_PREAMBLE at the start of each rule and block.

    The antlr option -preamble_first is similar, but inserts the
    code BLOCK_PREAMBLE_FIRST(PreambleFirst_123) where the symbol
    PreambleFirst_123 is equivalent to the first set defined by
    the #FirstSetSymbol described in Item #248.

#248. Generate symbol for first set of an alternative

        rr : #FirstSetSymbol(rr_FirstSet)  ( Foo | Bar ) ;

#216. Defer token fetch for C++ mode

    When the ANTLRParser class is built with the pre-processor option 
    ZZDEFER_FETCH defined, the fetch of new tokens by consume() is deferred
    until LA(i) or LT(i) is called. 

#215. Use reset() to reset DLGLexerBase
#188. Added pccts/h/DLG_stream_input.h
#180. Added ANTLRParser::getEofToken()
#173. -glms for Microsoft style filenames with -gl
#170. Suppression for predicates with lookahead depth >1

      Consider the following grammar with -ck 2 and the predicate in rule
      "a" with depth 2:

            r1  : (ab)* "@"
                ;

            ab  : a
                | b
                ;

            a   : (A B)? => <<p(LATEXT(2))>>? A B C
                ;

            b   : A B C
                ;

      Normally, the predicate would be hoisted into rule r1 in order to
      determine whether to call rule "ab".  However it should *not* be
      hoisted because, even if p is false, there is a valid alternative
      in rule b.  With "-mrhoistk on" the predicate will be suppressed.

      If "-info p" command line option is present the following information
      will appear in the generated code:

                while ( (LA(1)==A)
        #if 0

        Part (or all) of predicate with depth > 1 suppressed by alternative
            without predicate

        pred  <<  p(LATEXT(2))>>?
                  depth=k=2  ("=>" guard)  rule a  line 8  t1.g
          tree context:
            (root = A
               B
            )

        The token sequence which is suppressed: ( A B )
        The sequence of references which generate that sequence of tokens:

           1 to ab          r1/1       line 1     t1.g
           2 ab             ab/1       line 4     t1.g
           3 to b           ab/2       line 5     t1.g
           4 b              b/1        line 11    t1.g
           5 #token A       b/1        line 11    t1.g
           6 #token B       b/1        line 11    t1.g

        #endif

      A slightly more complicated example:

            r1  : (ab)* "@"
                ;

            ab  : a
                | b
                ;

            a   : (A B)? => <<p(LATEXT(2))>>? (A  B | D E)
                ;

            b   : <<q(LATEXT(2))>>? D E
                ;


      In this case, the sequence (D E) in rule "a" which lies behind
      the guard is used to suppress the predicate with context (D E)
      in rule b.

                while ( (LA(1)==A || LA(1)==D)
            #if 0

            Part (or all) of predicate with depth > 1 suppressed by alternative
                without predicate

            pred  <<  q(LATEXT(2))>>?
                              depth=k=2  rule b  line 11  t2.g
              tree context:
                (root = D
                   E
                )

            The token sequence which is suppressed: ( D E )
            The sequence of references which generate that sequence of tokens:

               1 to ab          r1/1       line 1     t2.g
               2 ab             ab/1       line 4     t2.g
               3 to a           ab/1       line 4     t2.g
               4 a              a/1        line 8     t2.g
               5 #token D       a/1        line 8     t2.g
               6 #token E       a/1        line 8     t2.g

            #endif
            &&
            #if 0

            pred  <<  p(LATEXT(2))>>?
                              depth=k=2  ("=>" guard)  rule a  line 8  t2.g
              tree context:
                (root = A
                   B
                )

            #endif

            (! ( LA(1)==A && LA(2)==B ) || p(LATEXT(2)) )  {
                ab();
                ...

#165. (Changed in MR13) option -newAST

      To create ASTs from an ANTLRTokenPtr antlr usually calls
      "new AST(ANTLRTokenPtr)".  This option generates a call
      to "newAST(ANTLRTokenPtr)" instead.  This allows a user
      to define a parser member function to create an AST object.

#161. (Changed in MR13) Switch -gxt inhibits generation of tokens.h

#158. (Changed in MR13) #header causes problem for pre-processors

      A user who runs the C pre-processor on antlr source suggested
      that another syntax be allowed.  With MR13 such directives
      such as #header, #pragma, etc. may be written as "\#header",
      "\#pragma", etc.  For escaping pre-processor directives inside
      a #header use something like the following:

            \#header
            <<
                \#include <stdio.h>
            >>

#155. (Changed in MR13) Context behind predicates can suppress

      With -mrhoist enabled the context behind a guarded predicate can
      be used to suppress other predicates.  Consider the following grammar:

        r0 : (r1)+;

        r1  : rp
            | rq
            ;
        rp  : <<p LATEXT(1)>>? B ;
        rq : (A)? => <<q LATEXT(1)>>? (A|B);

      In earlier versions both predicates "p" and "q" would be hoisted into
      rule r0. With MR12c predicate p is suppressed because the context which
      follows predicate q includes "B" which can "cover" predicate "p".  In
      other words, in trying to decide in r0 whether to call r1, it doesn't
      really matter whether p is false or true because, either way, there is
      a valid choice within r1.

#154. (Changed in MR13) Making hoist suppression explicit using <<nohoist>>

      A common error, even among experienced pccts users, is to code
      an init-action to inhibit hoisting rather than a leading action.
      An init-action does not inhibit hoisting.

      This was coded:

        rule1 : <<;>> rule2

      This is what was meant:

        rule1 : <<;>> <<;>> rule2

      With MR13, the user can code:

        rule1 : <<;>> <<nohoist>> rule2

      The following will give an error message:

        rule1 : <<nohoist>> rule2

      If the <<nohoist>> appears as an init-action rather than a leading
      action an error message is issued.  The meaning of an init-action
      containing "nohoist" is unclear: does it apply to just one
      alternative or to all alternatives ?

#151a. Addition of ANTLRParser::getLexer(), ANTLRTokenStream::getLexer()

      You must manually cast the ANTLRTokenStream to your program's
      lexer class. Because the name of the lexer's class is not fixed.
      Thus it is impossible to incorporate it into the DLGLexerBase
      class.

#151b.(Changed in MR12) ParserBlackBox member getLexer()

#150. (Changed in MR12) syntaxErrCount and lexErrCount now public

#149. (Changed in MR12) antlr option -info o (letter o for orphan)

      If there is more than one rule which is not referenced by any
      other rule then all such rules are listed.  This is useful for
      alerting one to rules which are not used, but which can still
      contribute to ambiguity.

#148. (Changed in MR11) #token names appearing in zztokens,token_tbl

      One can write:

            #token Plus ("+")             "\+"
            #token RP   ("(")             "\("
            #token COM  ("comment begin") "/\*"

      The string in parenthesis will be used in syntax error messages.

#146. (Changed in MR11) Option -treport for locating "difficult" alts

      It can be difficult to determine which alternatives are causing
      pccts to work hard to resolve an ambiguity.  In some cases the
      ambiguity is successfully resolved after much CPU time so there
      is no message at all.

      A rough measure of the amount of work being peformed which is
      independent of the CPU speed and system load is the number of
      tnodes created.  Using "-info t" gives information about the
      total number of tnodes created and the peak number of tnodes.

        Tree Nodes:  peak 1300k  created 1416k  lost 0

      It also puts in the generated C or C++ file the number of tnodes
      created for a rule (at the end of the rule).  However this
      information is not sufficient to locate the alternatives within
      a rule which are causing the creation of tnodes.

      Using:

             antlr -treport 100000 ....

      causes antlr to list on stdout any alternatives which require the
      creation of more than 100,000 tnodes, along with the lookahead sets
      for those alternatives.

      The following is a trivial case from the ansi.g grammar which shows
      the format of the report.  This report might be of more interest
      in cases where 1,000,000 tuples were created to resolve the ambiguity.

      -------------------------------------------------------------------------
        There were 0 tuples whose ambiguity could not be resolved
             by full lookahead
        There were 157 tnodes created to resolve ambiguity between:

          Choice 1: statement/2  line 475  file ansi.g
          Choice 2: statement/3  line 476  file ansi.g

            Intersection of lookahead[1] sets:

               IDENTIFIER

            Intersection of lookahead[2] sets:

               LPARENTHESIS     COLON            AMPERSAND        MINUS
               STAR             PLUSPLUS         MINUSMINUS       ONESCOMPLEMENT
               NOT              SIZEOF           OCTALINT         DECIMALINT
               HEXADECIMALINT   FLOATONE         FLOATTWO         IDENTIFIER
               STRING           CHARACTER
      -------------------------------------------------------------------------

#143. (Changed in MR11) Optional ";" at end of #token statement

      Fixes problem of:

            #token X "x"

            <<