Source/Pccts/KNOWN_PROBLEMS.txt

    =======================================================
    Known Problems In PCCTS - Last revised 14 November 1998
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#17. The dlg fix for handling characters up to 255 is incorrect.

    See item #207.

    Reported by Frank Hartmann.
        
#16. A note about "&&" predicates (Mike Dimmick)

    Mike Dimmick has pointed out a potential pitfall in the use of the
    "&&" style predicate.  Consider:
    
         r0: (g)? => <<P>>?  r1
             | ...
             ;
         r1: A | B;
         
    If the context guard g is not a subset of the lookahead context for r1
    (in other words g is neither A nor B) then the code may execute r1 
    even when the lookahead context is not satisfied.  This is an error
    by the person coding the grammer, and the error should be reported to
    the user, but it isn't. expect.  Some examples I've run seem to
    indicate that such an error actually results in the rule becoming
    unreachable.
    
    When g is properly coded the code is correct, the problem is when g
    is not properly coded.
    
    A second problem reported by Mike Dimmick is that the test for a
    failed validation predicate is equivalent to a test on the predicate
    along.  In other words, if the "&&" has not been hoisted then it may
    falsely report a validation error.

#15. (Changed in MR23) Warning for LT(i), LATEXT(i) in token match actions

    An bug (or at least an oddity) is that a reference to LT(1), LA(1),
    or LATEXT(1) in an action which immediately follows a token match
    in a rule refers to the token matched, not the token which is in
    the lookahead buffer.  Consider:

        r : abc <<action alpha>> D <<action beta>> E;

    In this case LT(1) in action alpha will refer to the next token in
    the lookahead buffer ("D"), but LT(1) in action beta will refer to
    the token matched by D - the preceding token.

    A warning has been added which warns users about this when an action
    following a token match contains a reference to LT(1), LA(1), or LATEXT(1).

    This behavior should be changed, but it appears in too many programs
    now.  Another problem, perhaps more significant, is that the obvious
    fix (moving the consume() call to before the action) could change the 
    order in which input is requested and output appears in existing programs.

    This problem was reported, along with a fix by Benjamin Mandel
    (beny@sd.co.il).  However, I felt that changing the behavior was too
    dangerous for existing code.

#14. Parsing bug in dlg

    THM: I have been unable to reproduce this problem.

    Reported by Rick Howard Mijenix Corporation (rickh@mijenix.com).

    The regular expression parser (in rexpr.c) fails while
    trying to parse the following regular expression:

            {[a-zA-Z]:}(\\\\[a-zA-Z0-9]*)+

    See my comment in the following excerpt from rexpr.c:

    /*
     * <regExpr>        ::= <andExpr> ( '|' {<andExpr>} )*
     *
     * Return -1 if syntax error
     * Return  0 if none found
     * Return  1 if a regExrp was found
     */
	static
	regExpr(g)
	GraphPtr g;
	{
	    Graph g1, g2;
	
	    if ( andExpr(&g1) == -1 )
	    {
	        return -1;
	    }
	
	    while ( token == '|' )
	    {
	        int a;
	        next();
	        a = andExpr(&g2);
	        if ( a == -1 ) return -1;   /* syntax error below */
	        else if ( !a ) return 1;    /* empty alternative */
	        g1 = BuildNFA_AorB(g1, g2);
	    }
	
	    if ( token!='\0' ) return -1;
	*****
	***** It appears to fail here becuause token is 125 - the closing '}'
	***** If I change it to:
	*****    if ( token!='\0' && token!='}' && token!= ')' ) return -1;
	*****
	***** It succeeds, but I'm not sure this is the corrrect approach.
	*****
	    *g = g1;
	    return 1;
	}

#13. dlg reports an invalid range for: [\0x00-\0xff]

    Diagnosed by Piotr Eljasiak (eljasiak@no-spam.zt.gdansk.tpsa.pl):

    Fixed in MR16.

#12. Strings containing comment actions

     Sequences that looked like C style comments appearing in string
     literals are improperly parsed by antlr/dlg.

        << fprintf(out," /* obsolete */ ");

     For this case use:

        << fprintf(out," \/\* obsolete \*\/ ");

     Reported by K.J. Cummings (cummings@peritus.com).

#11. User hook for deallocation of variables on guess fail

     The mechanism outlined in Item #108 works only for
     heap allocated variables.

#10. Label re-initialization in ( X {y:Y} )*

     If a label assignment is optional and appears in a
     (...)* or (...)+ block it will not be reset to NULL
     when it is skipped by a subsequent iteration.

     Consider the example:

            ( X { y:Y })* Z

     with input:

            X Y X Z

     The first time through the block Y will be matched and
     y will be set to point to the token.  On the second
     iteration of the (...)* block there is no match for Y.
     But y will not be reset to NULL, as the user might
     expect, it will contain a reference to the Y that was
     matched in the first iteration.

     The work-around is to manually reset y:

            ( X << y = NULL; >> { y:Y } )* Z

        or

            ( X ( y:Y | << y = NULL; >> /* epsilon */ ) )* Z

     Reported by Jeff Vincent (JVincent@novell.com).

#9. PCCTAST.h PCCTSAST::setType() is a noop

#8. #tokdefs with ~Token and .

    THM: I have been unable to reproduce this problem.

    When antlr uses #tokdefs to define tokens the fields of
    #errclass and #tokclass do not get properly defined.
    When it subsequently attempts to take the complement of
    the set of tokens (using ~Token or .) it can refer to
    tokens which don't have names, generating a fatal error.

#7. DLG crashes on some invalid inputs

    THM:  In MR20 have fixed the most common cases.

    The following token defintion will cause DLG to crash.

        #token "()"

    Reported by  Mengue Olivier (dolmen@bigfoot.com).

#6. On MS systems \n\r is treated as two new lines

    Fixed.

#5. Token expressions in #tokclass

    #errclass does not support TOK1..TOK2 or ~TOK syntax.
    #tokclass does not support ~TOKEN syntax

    A workaround for #errclass TOK1..TOK2 is to use a
    #tokclass.

    Reported by Dave Watola (dwatola@amtsun.jpl.nasa.gov)

#4. A #tokdef must appear "early" in the grammar file.

    The "early" section of the grammar file is the only
    place where the following directives may appear:

        #header
        #first
        #tokdefs
        #parser

    Any other kind of statement signifiies the end of the
    "early" section.

#3. Use of PURIFY macro for C++ mode

    Item #93 of the CHANGES_FROM_1.33 describes the use of
    the PURIFY macro to zero arguments to be passed by
    upward inheritance.

        #define PURIFY(r, s) memset((char *) &(r), '\0', (s));

    This may not be the right thing to do for C++ objects that
    have constructors.  Reported by Bonny Rais (bonny@werple.net.au).

    For those cases one should #define PURIFY to be an empty macro
    in the #header or #first actions.

#2. Fixed in 1.33MR10 - See CHANGES_FROM_1.33 Item #80.

#1. The quality of support for systems with 8.3 file names leaves
    much to be desired.  Since the kit is distributed using the
    long file names and the make file uses long file names it requires
    some effort to generate.  This will probably not be changed due
    to the large number of systems already written using the long
    file names.