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242 lines
7.6 KiB
Plaintext
242 lines
7.6 KiB
Plaintext
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=======================================================
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Known Problems In PCCTS - Last revised 14 November 1998
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=======================================================
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#17. The dlg fix for handling characters up to 255 is incorrect.
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See item #207.
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Reported by Frank Hartmann.
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#16. A note about "&&" predicates (Mike Dimmick)
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Mike Dimmick has pointed out a potential pitfall in the use of the
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"&&" style predicate. Consider:
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r0: (g)? => <<P>>? r1
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| ...
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;
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r1: A | B;
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If the context guard g is not a subset of the lookahead context for r1
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(in other words g is neither A nor B) then the code may execute r1
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even when the lookahead context is not satisfied. This is an error
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by the person coding the grammar, and the error should be reported to
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the user, but it isn't. expect. Some examples I've run seem to
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indicate that such an error actually results in the rule becoming
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unreachable.
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When g is properly coded the code is correct, the problem is when g
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is not properly coded.
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A second problem reported by Mike Dimmick is that the test for a
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failed validation predicate is equivalent to a test on the predicate
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along. In other words, if the "&&" has not been hoisted then it may
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falsely report a validation error.
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#15. (Changed in MR23) Warning for LT(i), LATEXT(i) in token match actions
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An bug (or at least an oddity) is that a reference to LT(1), LA(1),
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or LATEXT(1) in an action which immediately follows a token match
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in a rule refers to the token matched, not the token which is in
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the lookahead buffer. Consider:
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r : abc <<action alpha>> D <<action beta>> E;
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In this case LT(1) in action alpha will refer to the next token in
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the lookahead buffer ("D"), but LT(1) in action beta will refer to
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the token matched by D - the preceding token.
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A warning has been added which warns users about this when an action
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following a token match contains a reference to LT(1), LA(1), or LATEXT(1).
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This behavior should be changed, but it appears in too many programs
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now. Another problem, perhaps more significant, is that the obvious
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fix (moving the consume() call to before the action) could change the
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order in which input is requested and output appears in existing programs.
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This problem was reported, along with a fix by Benjamin Mandel
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(beny@sd.co.il). However, I felt that changing the behavior was too
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dangerous for existing code.
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#14. Parsing bug in dlg
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THM: I have been unable to reproduce this problem.
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Reported by Rick Howard Mijenix Corporation (rickh@mijenix.com).
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The regular expression parser (in rexpr.c) fails while
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trying to parse the following regular expression:
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{[a-zA-Z]:}(\\\\[a-zA-Z0-9]*)+
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See my comment in the following excerpt from rexpr.c:
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/*
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* <regExpr> ::= <andExpr> ( '|' {<andExpr>} )*
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*
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* Return -1 if syntax error
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* Return 0 if none found
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* Return 1 if a regExrp was found
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*/
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static
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regExpr(g)
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GraphPtr g;
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{
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Graph g1, g2;
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if ( andExpr(&g1) == -1 )
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{
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return -1;
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}
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while ( token == '|' )
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{
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int a;
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next();
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a = andExpr(&g2);
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if ( a == -1 ) return -1; /* syntax error below */
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else if ( !a ) return 1; /* empty alternative */
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g1 = BuildNFA_AorB(g1, g2);
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}
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if ( token!='\0' ) return -1;
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*****
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***** It appears to fail here becuause token is 125 - the closing '}'
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***** If I change it to:
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***** if ( token!='\0' && token!='}' && token!= ')' ) return -1;
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*****
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***** It succeeds, but I'm not sure this is the corrrect approach.
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*****
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*g = g1;
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return 1;
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}
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#13. dlg reports an invalid range for: [\0x00-\0xff]
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Diagnosed by Piotr Eljasiak (eljasiak@no-spam.zt.gdansk.tpsa.pl):
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Fixed in MR16.
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#12. Strings containing comment actions
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Sequences that looked like C style comments appearing in string
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literals are improperly parsed by antlr/dlg.
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<< fprintf(out," /* obsolete */ ");
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For this case use:
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<< fprintf(out," \/\* obsolete \*\/ ");
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Reported by K.J. Cummings (cummings@peritus.com).
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#11. User hook for deallocation of variables on guess fail
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The mechanism outlined in Item #108 works only for
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heap allocated variables.
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#10. Label re-initialization in ( X {y:Y} )*
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If a label assignment is optional and appears in a
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(...)* or (...)+ block it will not be reset to NULL
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when it is skipped by a subsequent iteration.
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Consider the example:
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( X { y:Y })* Z
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with input:
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X Y X Z
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The first time through the block Y will be matched and
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y will be set to point to the token. On the second
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iteration of the (...)* block there is no match for Y.
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But y will not be reset to NULL, as the user might
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expect, it will contain a reference to the Y that was
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matched in the first iteration.
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The work-around is to manually reset y:
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( X << y = NULL; >> { y:Y } )* Z
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or
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( X ( y:Y | << y = NULL; >> /* epsilon */ ) )* Z
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Reported by Jeff Vincent (JVincent@novell.com).
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#9. PCCTAST.h PCCTSAST::setType() is a noop
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#8. #tokdefs with ~Token and .
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THM: I have been unable to reproduce this problem.
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When antlr uses #tokdefs to define tokens the fields of
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#errclass and #tokclass do not get properly defined.
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When it subsequently attempts to take the complement of
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the set of tokens (using ~Token or .) it can refer to
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tokens which don't have names, generating a fatal error.
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#7. DLG crashes on some invalid inputs
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THM: In MR20 have fixed the most common cases.
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The following token definition will cause DLG to crash.
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#token "()"
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Reported by Mengue Olivier (dolmen@bigfoot.com).
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#6. On MS systems \n\r is treated as two new lines
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Fixed.
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#5. Token expressions in #tokclass
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#errclass does not support TOK1..TOK2 or ~TOK syntax.
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#tokclass does not support ~TOKEN syntax
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A workaround for #errclass TOK1..TOK2 is to use a
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#tokclass.
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Reported by Dave Watola (dwatola@amtsun.jpl.nasa.gov)
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#4. A #tokdef must appear "early" in the grammar file.
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The "early" section of the grammar file is the only
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place where the following directives may appear:
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#header
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#first
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#tokdefs
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#parser
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Any other kind of statement signifiies the end of the
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"early" section.
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#3. Use of PURIFY macro for C++ mode
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Item #93 of the CHANGES_FROM_1.33 describes the use of
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the PURIFY macro to zero arguments to be passed by
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upward inheritance.
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#define PURIFY(r, s) memset((char *) &(r), '\0', (s));
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This may not be the right thing to do for C++ objects that
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have constructors. Reported by Bonny Rais (bonny@werple.net.au).
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For those cases one should #define PURIFY to be an empty macro
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in the #header or #first actions.
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#2. Fixed in 1.33MR10 - See CHANGES_FROM_1.33 Item #80.
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#1. The quality of support for systems with 8.3 file names leaves
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much to be desired. Since the kit is distributed using the
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long file names and the make file uses long file names it requires
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some effort to generate. This will probably not be changed due
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to the large number of systems already written using the long
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file names.
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