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* Soon ** gnulib Bruno notes: > I haven't looked deeply, but it strikes me that gnulib/lib/bitset/array.c > does not make use of the 'ffsl' function, nor or the 'integer_length_l' > function. Maybe because in Bison, all bitsets are so dense that it does > not give a performance advantage? ** Cex *** Improve gnulib Don't do this (counterexample.c): // This is the fastest way to get the tail node from the gl_list API. gl_list_node_t list_get_end (gl_list_t list) { gl_list_node_t sentinel = gl_list_add_last (list, NULL); gl_list_node_t res = gl_list_previous_node (list, sentinel); gl_list_remove_node (list, sentinel); return res; } *** Ambiguous rewriting If the user is stupid enough to have equal rules, then the derivations are harder to read: Reduce/reduce conflict on tokens $end, "+", "⊕": 2 exp: exp "+" exp . 3 exp: exp "+" exp . Example exp "+" exp • First derivation exp ::=[ exp "+" exp • ] Example exp "+" exp • Second derivation exp ::=[ exp "+" exp • ] Do we care about this? In color, we use twice the same color here, but we could try to use the same color for the same rule. *** XML reports Show the counterexamples. This is going to be really hard and/or painful. Unless we play it dumb (little structure). ** Bistromathic - How about not evaluating incomplete lines when the text is not finished (as shells do). ** Questions *** Java - Should i18n be part of the Lexer? Currently it's a static method of Lexer. - is there a migration path that would allow to use TokenKinds in yylex? - define the tokens as an enum too. - promote YYEOF rather than EOF. ** YYerror https://git.savannah.gnu.org/gitweb/?p=gettext.git;a=blob;f=gettext-runtime/intl/plural.y;h=a712255af4f2f739c93336d4ff6556d932a426a5;hb=HEAD should be updated to not use YYERRCODE. Returning an undef token is good enough. ** Java *** calc.at Stop hard-coding "Calc". Adjust local.at (look for FIXME). ** A dev warning for b4_ Maybe we should check for m4_ and b4_ leaking out of the m4 processing, as Autoconf does. It would have caught over-quotation issues. ** doc I feel it's ugly to use the GNU style to declare functions in the doc. It generates tons of white space in the page, and may contribute to bad page breaks. ** consistency token vs terminal. ** api.token.raw The YYUNDEFTOK could be assigned a semantic value so that yyerror could be used to report invalid lexemes. ** push parsers Consider deprecating impure push parsers. They add a lot of complexity, for a bad feature. On the other hand, that would make it much harder to sit push parsers on top of pull parser. Which is currently not relevant, since push parsers are measurably slower. ** %define parse.error formatted How about pushing Bistromathic's yyreport_syntax_error as another standard way to generate the error message, and leave to the user the task of providing the message formats? Currently in bistro, it reads: const char * error_format_string (int argc) { switch (argc) { default: /* Avoid compiler warnings. */ case 0: return _("%@: syntax error"); case 1: return _("%@: syntax error: unexpected %u"); // TRANSLATORS: '%@' is a location in a file, '%u' is an // "unexpected token", and '%0e', '%1e'... are expected tokens // at this point. // // For instance on the expression "1 + * 2", you'd get // // 1.5: syntax error: expected - or ( or number or function or variable before * case 2: return _("%@: syntax error: expected %0e before %u"); case 3: return _("%@: syntax error: expected %0e or %1e before %u"); case 4: return _("%@: syntax error: expected %0e or %1e or %2e before %u"); case 5: return _("%@: syntax error: expected %0e or %1e or %2e or %3e before %u"); case 6: return _("%@: syntax error: expected %0e or %1e or %2e or %3e or %4e before %u"); case 7: return _("%@: syntax error: expected %0e or %1e or %2e or %3e or %4e or %5e before %u"); case 8: return _("%@: syntax error: expected %0e or %1e or %2e or %3e or %4e or %5e or %6e before %u"); } } The message would have to be generated in a string, and pushed to yyerror. Which will be a pain in the neck in yacc.c. If we want to do that, we should think very carefully about the syntax of the format string. ** yyclearin does not invoke the lookahead token's %destructor https://lists.gnu.org/r/bug-bison/2018-02/msg00000.html Rici: > Modifying yyclearin so that it calls yydestruct seems like the simplest > solution to this issue, but it is conceivable that such a change would > break programs which already perform some kind of workaround in order to > destruct the lookahead symbol. So it might be necessary to use some kind of > compatibility %define, or to create a new replacement macro with a > different name such as yydiscardin. > > At a minimum, the fact that yyclearin does not invoke the %destructor > should be highlighted in the documentation, since it is not at all obvious. ** Issues in i18n Les catégories d'avertissements incluent : conflicts-sr conflits S/R (activé par défaut) conflicts-rr conflits R/R (activé par défaut) dangling-alias l'alias chaîne n'est pas attaché à un symbole deprecated construction obsolète empty-rule règle vide sans %empty midrule-values valeurs de règle intermédiaire non définies ou inutilisées precedence priorité et associativité inutiles yacc incompatibilités avec POSIX Yacc other tous les autres avertissements (activé par défaut) all tous les avertissements sauf « dangling-alias » et « yacc » no-CATEGORY désactiver les avertissements dans CATEGORIE none désactiver tous les avertissements error[=CATEGORY] traiter les avertissements comme des erreurs Line -1 and -3 should mention CATEGORIE, not CATEGORY. * Bison 3.8 ** Rewrite glr.cc Get rid of scaffolding in glr.c. ** Unit rules / Injection rules (Akim Demaille) Maybe we could expand unit rules (or "injections", see https://homepages.cwi.nl/~daybuild/daily-books/syntax/2-sdf/sdf.html), i.e., transform exp: arith | bool; arith: exp '+' exp; bool: exp '&' exp; into exp: exp '+' exp | exp '&' exp; when there are no actions. This can significantly speed up some grammars. I can't find the papers. In particular the book 'LR parsing: Theory and Practice' is impossible to find, but according to 'Parsing Techniques: a Practical Guide', it includes information about this issue. Does anybody have it? ** clean up (Akim Demaille) Do not work on these items now, as I (Akim) have branches with a lot of changes in this area (hitting several files), and no desire to have to fix conflicts. Addressing these items will happen after my branches have been merged. *** lalr.c Introduce a goto struct, and use it in place of from_state/to_state. Rename states1 as path, length as pathlen. Introduce inline functions for things such as nullable[*rp - ntokens] where we need to map from symbol number to nterm number. There are probably a significant part of the relations management that should be migrated on top of a bitsetv. *** closure It should probably take a "state*" instead of two arguments. *** traces The "automaton" and "set" categories are not so useful. We should probably introduce lr(0) and lalr, just the way we have ielr categories. The "closure" function is too verbose, it should probably have its own category. "set" can still be used for summarizing the important sets. That would make tests easy to maintain. *** complain.* Rename these guys as "diagnostics.*" (or "diagnose.*"), since that's the name they have in GCC, clang, etc. Likewise for the complain_* series of functions. *** ritem states/nstates, rules/nrules, ..., ritem/nritems Fix the latter. * D programming language There's a number of features that are missing, here sorted in _suggested_ order of implementation. When copying code from other skeletons, keep the comments exactly as they are. Keep the same variable names. If you change the wording in one place, do it in the others too. In other words: make sure to keep the maintenance *simple* by avoiding any gratuitous difference. ** Rename the D example Move the current content of examples/d into examples/d/simple. ** Create a second example Duplicate examples/d/simple into examples/d/calc. ** Add location tracking to d/calc Look at the examples in the other languages to see how to do that. ** yysymbol_name The SymbolKind is an enum. For a given SymbolKind we want to get its string representation. Currently it's a separate table in the parser that does that: /* Symbol kinds. */ public enum SymbolKind { S_YYEMPTY = -2, /* No symbol. */ S_YYEOF = 0, /* "end of file" */ S_YYerror = 1, /* error */ S_YYUNDEF = 2, /* "invalid token" */ S_EQ = 3, /* "=" */ ... S_input = 14, /* input */ S_line = 15, /* line */ S_exp = 16, /* exp */ }; ... /* YYTNAME[SYMBOL-NUM] -- String name of the symbol SYMBOL-NUM. First, the terminals, then, starting at \a yyntokens_, nonterminals. */ private static immutable string[] yytname_ = [ "\"end of file\"", "error", "\"invalid token\"", "\"=\"", "\"+\"", "\"-\"", "\"*\"", "\"/\"", "\"(\"", "\")\"", "\"end of line\"", "\"number\"", "UNARY", "$accept", "input", "line", "exp", null ]; ... So to get a symbol kind, one runs `yytname_[yykind]`. Is there a way to attach this conversion to string to SymbolKind? In Java for instance, we have: public enum SymbolKind { S_YYEOF(0), /* "end of file" */ S_YYerror(1), /* error */ S_YYUNDEF(2), /* "invalid token" */ ... S_input(16), /* input */ S_line(17), /* line */ S_exp(18); /* exp */ private final int yycode_; SymbolKind (int n) { this.yycode_ = n; } ... /* YYNAMES_[SYMBOL-NUM] -- String name of the symbol SYMBOL-NUM. First, the terminals, then, starting at \a YYNTOKENS_, nonterminals. */ private static final String[] yynames_ = yynames_init(); private static final String[] yynames_init() { return new String[] { i18n("end of file"), i18n("error"), i18n("invalid token"), "!", "+", "-", "*", "/", "^", "(", ")", "=", i18n("end of line"), i18n("number"), "NEG", "$accept", "input", "line", "exp", null }; } /* The user-facing name of this symbol. */ public final String getName() { return yynames_[yycode_]; } }; which allows to write more naturally `yykind.getName()` rather than `yytname_[yykind]`. Is there something comparable in (idiomatic) D? ** Change the return value of yylex Historically people were allowed to return any int from the scanner (which is convenient and allows `return '+'` from the scanner). Akim tends to see this as an error, we should restrict the return values to TokenKind (not to be confused with SymbolKind). In the case of D, without the history, we have the choice to support or not `int`. If we want to _keep_ `int`, is there a way, say via introspection, to support both signatures of yylex? If we don't keep `int`, just move to TokenKind. ** Documentation Write documentation about D support in doc/bison.texi. Imitate the Java documentation. You should be more succinct IMHO. ** Complete Symbols The current interface from the scanner to the parser is somewhat clumsy: the token kind is returned by yylex, but the value and location are stored in the scanner. This reflects the fact that the implementation of the parser uses three variables to deal with each parsed symbol: its kind, its value, its location. So today the scanner of examples/d/calc.d (no locations) looks like: if (input.front.isNumber) { import std.conv : parse; semanticVal_.ival = input.parse!int; return TokenKind.NUM; } and the generated parser: /* Read a lookahead token. */ if (yychar == TokenKind.YYEMPTY) { yychar = yylex (); yylval = yylexer.semanticVal; } The parser class should feature a `Symbol` type which binds together kind, value and location, and the scanner should be able to return an instance of that type. Something like if (input.front.isNumber) { import std.conv : parse; return parser.Symbol (TokenKind.NUM, input.parse!int); } ** Token Constructors In the previous example it is possible to mix incorrectly kinds and values, and for instance: return parser.Symbol (TokenKind.NUM, "Hello, World!\n"); attaches a string value to NUM kind (wrong, of course). When api.token.constructor is set, in C++, Bison generated "token constructors": parser.make_NUM. parser.make_PLUS, parser.make_STRING, etc. The previous example becomes return parser.make_NUM ("Hello, World!\n"); which would easily be caught by the type checker. ** Lookahead Correction Add support for LAC to the D skeleton. It should not be too hard: look how this is done in lalr1.cc, and mock it. ** Push Parser Add support for push parser. Do not start a nice skeleton, just enhance the current one to support push parsers. This is going to be a tougher nut to crack. First, you need to understand well how the push parser is expected to work. To this end: - read the doc - look at examples/c/pushcalc - create an example of a Java push parser. - have a look at the generated parser in Java, which has the advantage of being already based on a parser object, instead of just a function. The C case is harder to read, but it may help too. Keep in mind that because there's no object to maintain state, the C push parser uses some struct (yypstate) to preserve this state. We don't need this in D, the parser object will suffice. I think working directly on the skeleton to add push-parser support is not the simplest path. I suggest that you (1) transform a generated parser into a push parser by hand, and then (2) transform lalr1.d to generate such a parser. Use `git commit` frequently to make sure you keep track of your progress. *** (1.a) Prepare pull parser by hand Copy again one of the D examples into say examples/d/pushcalc. Also check-in the generated parser to facilitate experimentation. - find local variables of yyparse should become members of the parser object (so that we preserve state from one call to the next). - do it in your generated D parser. We don't need an equivalent for yypstate, because we already have it: that the parser object itself. - have your *pull*-parser (i.e., the good old yy::parser::parse()) work properly this way. Write and run tests. That's one of the reasons I suggest using examples/d/calc as a starting point: it already has tests, you can/should add more. At this point you have a pull-parser which you prepared to turn into a push-parser. *** (1.b) Turn pull parser into push parser by hand - look again at how push parsers are implemented in Java/C to see what needs to change in yyparse so that the control is inverted: parse() will be *given* the tokens, instead of having to call yylex itself. When I say "look at C", I think your best option are (i) yacc.c (look for b4_push_if) and (ii) examples/c/pushcalc. - rename parse() as push_parse(Symbol yyla) (or push_parse(TokenKind, Value, Location)) that takes the symbol as argument. That's the push parser we are looking for. - define a new parse() function which has the same signature as the usual pull-parser, that repeatedly calls the push_parse function. Something like this: int parse () { int status = 0; do { status = this->push_parse (yylex()); } while (status == YYPUSH_MORE); return status; } - show me that parser, so that we can validate the approach. *** (2) Port that into the skeleton - once we agree on the API of the push parser, implement it into lalr1.d. You will probaby need help on this regard, but imitation, again, should help. - have example/d/pushcalc work properly and pass tests - add tests in the "real" test suite. Do that in tests/calc.at. I can help. - document ** GLR Parser This is very ambitious. That's the final boss. There are currently no "clean" implementation to get inspiration from. glr.c is very clean but: - is low-level C - is a different skeleton from yacc.c glr.cc is (currently) an ugly hack: a C++ shell around glr.c. Valentin Tolmer is currently rewriting glr.cc to be clean C++, but he is not finished. There will be a lot a common code between lalr1.cc and glr.cc, so eventually I would like them to be fused into a single skeleton, supporting both deterministic and generalized parsing. It would be great for D to also support this. The basic ideas of GLR are explained here: https://www.codeproject.com/Articles/5259825/GLR-Parsing-in-Csharp-How-to-Use-The-Most-Powerful * Better error messages The users are not provided with enough tools to forge their error messages. See for instance "Is there an option to change the message produced by YYERROR_VERBOSE?" by Simon Sobisch, on bison-help. See also https://www.cs.tufts.edu/~nr/cs257/archive/clinton-jefferey/lr-error-messages.pdf https://research.swtch.com/yyerror http://gallium.inria.fr/~fpottier/publis/fpottier-reachability-cc2016.pdf * Modernization Fix data/skeletons/yacc.c so that it defines YYPTRDIFF_T properly for modern and older C++ compilers. Currently the code defaults to defining it to 'long' for non-GCC compilers, but it should use the proper C++ magic to define it to the same type as the C ptrdiff_t type. * Completion Several features are not available in all the back-ends. - lac: D, Java (easy) - push parsers: glr.c, glr.cc, lalr1.cc (not very difficult) - token constructors: Java, C, D (a bit difficult) - glr: D, Java (super difficult) * Bugs ** Autotest has quotation issues tests/input.at:1730:AT_SETUP([%define errors]) -> $ ./tests/testsuite -l | grep errors | sed q 38: input.at:1730 errors * Short term ** Get rid of YYPRINT and b4_toknum Besides yytoknum is wrong when api.token.raw is defined. ** Better design for diagnostics The current implementation of diagnostics is ad hoc, it grew organically. It works as a series of calls to several functions, with dependency of the latter calls on the former. For instance: complain (&sym->location, sym->content->status == needed ? complaint : Wother, _("symbol %s is used, but is not defined as a token" " and has no rules; did you mean %s?"), quote_n (0, sym->tag), quote_n (1, best->tag)); if (feature_flag & feature_caret) location_caret_suggestion (sym->location, best->tag, stderr); We should rewrite this in a more FP way: 1. build a rich structure that denotes the (complete) diagnostic. "Complete" in the sense that it also contains the suggestions, the list of possible matches, etc. 2. send this to the pretty-printing routine. The diagnostic structure should be sufficient so that we can generate all the 'format' of diagnostics, including the fixits. If properly done, this diagnostic module can be detached from Bison and be put in gnulib. It could be used, for instance, for errors caught by xgettext. There's certainly already something alike in GCC. At least that's the impression I get from reading the "-fdiagnostics-format=FORMAT" part of this page: https://gcc.gnu.org/onlinedocs/gcc/Diagnostic-Message-Formatting-Options.html ** Graphviz display code thoughts The code for the --graph option is over two files: print_graph, and graphviz. This is because Bison used to also produce VCG graphs, but since this is no longer true, maybe we could consider these files for fusion. An other consideration worth noting is that print_graph.c (correct me if I am wrong) should contain generic functions, whereas graphviz.c and other potential files should contain just the specific code for that output format. It will probably prove difficult to tell if the implementation is actually generic whilst only having support for a single format, but it would be nice to keep stuff a bit tidier: right now, the construction of the bitset used to show reductions is in the graphviz-specific code, and on the opposite side we have some use of \l, which is graphviz-specific, in what should be generic code. Little effort seems to have been given to factoring these files and their print{,-xml} counterpart. We would very much like to re-use the pretty format of states from .output for the graphs, etc. Since graphviz dies on medium-to-big grammars, maybe consider an other tool? ** push-parser Check it too when checking the different kinds of parsers. And be sure to check that the initial-action is performed once per parsing. ** m4 names b4_shared_declarations is no longer what it is. Make it b4_parser_declaration for instance. ** yychar in lalr1.cc There is a large difference bw maint and master on the handling of yychar (which was removed in lalr1.cc). See what needs to be back-ported. /* User semantic actions sometimes alter yychar, and that requires that yytoken be updated with the new translation. We take the approach of translating immediately before every use of yytoken. One alternative is translating here after every semantic action, but that translation would be missed if the semantic action invokes YYABORT, YYACCEPT, or YYERROR immediately after altering yychar. In the case of YYABORT or YYACCEPT, an incorrect destructor might then be invoked immediately. In the case of YYERROR, subsequent parser actions might lead to an incorrect destructor call or verbose syntax error message before the lookahead is translated. */ /* Make sure we have latest lookahead translation. See comments at user semantic actions for why this is necessary. */ yytoken = yytranslate_ (yychar); ** Get rid of fake #lines [Bison: ...] Possibly as simple as checking whether the column number is nonnegative. I have seen messages like the following from GCC. <built-in>:0: fatal error: opening dependency file .deps/libltdl/argz.Tpo: No such file or directory ** Discuss about %printer/%destroy in the case of C++. It would be very nice to provide the symbol classes with an operator<< and a destructor. Unfortunately the syntax we have chosen for %destroy and %printer make them hard to reuse. For instance, the user is invited to write something like %printer { debug_stream() << $$; } <my_type>; which is hard to reuse elsewhere since it wants to use "debug_stream()" to find the stream to use. The same applies to %destroy: we told the user she could use the members of the Parser class in the printers/destructors, which is not good for an operator<< since it is no longer bound to a particular parser, it's just a (standalone symbol). * Various ** Rewrite glr.cc in C++ (Valentin Tolmer) As a matter of fact, it would be very interesting to see how much we can share between lalr1.cc and glr.cc. Most of the skeletons should be common. It would be a very nice source of inspiration for the other languages. Valentin Tolmer is working on this. ** yychar == YYEMPTY The code in yyerrlab reads: if (yychar <= YYEOF) { /* Return failure if at end of input. */ if (yychar == YYEOF) YYABORT; } There are only two yychar that can be <= YYEOF: YYEMPTY and YYEOF. But I can't produce the situation where yychar is YYEMPTY here, is it really possible? The test suite does not exercise this case. This shows that it would be interesting to manage to install skeleton coverage analysis to the test suite. * From lalr1.cc to yacc.c ** Single stack Merging the three stacks in lalr1.cc simplified the code, prompted for other improvements and also made it faster (probably because memory management is performed once instead of three times). I suggest that we do the same in yacc.c. (Some time later): it's also very nice to have three stacks: it's more dense as we don't lose bits to padding. For instance the typical stack for states will use 8 bits, while it is likely to consume 32 bits in a struct. We need trustworthy benchmarks for Bison, for all our backends. Akim has a few things scattered around; we need to put them in the repo, and make them more useful. * Report ** Figures Some statistics about the grammar and the parser would be useful, especially when asking the user to send some information about the grammars she is working on. We should probably also include some information about the variables (I'm not sure for instance we even specify what LR variant was used). ** GLR How would Paul like to display the conflicted actions? In particular, what when two reductions are possible on a given lookahead token, but one is part of $default. Should we make the two reductions explicit, or just keep $default? See the following point. ** Disabled Reductions See 'tests/conflicts.at (Defaulted Conflicted Reduction)', and decide what we want to do. ** Documentation Extend with error productions. The hard part will probably be finding the right rule so that a single state does not exhibit too many yet undocumented ''features''. Maybe an empty action ought to be presented too. Shall we try to make a single grammar with all these features, or should we have several very small grammars? * Extensions ** More languages? Well, only if there is really some demand for it. *** PHP https://github.com/scfc/bison-php/blob/master/data/lalr1.php *** Python https://lists.gnu.org/r/bison-patches/2013-09/msg00000.html and following ** Multiple start symbols Would be very useful when parsing closely related languages. The idea is to declare several start symbols, for instance %start stmt expr %% stmt: ... expr: ... and to generate parse(), parse_stmt() and parse_expr(). Technically, the above grammar would be transformed into %start yy_start %token YY_START_STMT YY_START_EXPR %% yy_start: YY_START_STMT stmt | YY_START_EXPR expr so that there are no new conflicts in the grammar (as would undoubtedly happen with yy_start: stmt | expr). Then adjust the skeletons so that this initial token (YY_START_STMT, YY_START_EXPR) be shifted first in the corresponding parse function. ** %include This is a popular demand. We already made many changes in the parser that should make this reasonably easy to implement. Bruce Mardle <marblypup@yahoo.co.uk> https://lists.gnu.org/archive/html/bison-patches/2015-09/msg00000.html However, there are many other things to do before having such a feature, because I don't want a % equivalent to #include (which we all learned to hate). I want something that builds "modules" of grammars, and assembles them together, paying attention to keep separate bits separated, in pseudo name spaces. ** Push parsers There is demand for push parsers in Java and C++. And GLR I guess. ** Generate code instead of tables This is certainly quite a lot of work. See http://citeseerx.ist.psu.edu/viewdoc/summary?doi=10.1.1.50.4539. ** $-1 We should find a means to provide an access to values deep in the stack. For instance, instead of baz: qux { $$ = $<foo>-1 + $<bar>0 + $1; } we should be able to have: foo($foo) bar($bar) baz($bar): qux($qux) { $baz = $foo + $bar + $qux; } Or something like this. ** %if and the like It should be possible to have %if/%else/%endif. The implementation is not clear: should it be lexical or syntactic. Vadim Maslow thinks it must be in the scanner: we must not parse what is in a switched off part of %if. Akim Demaille thinks it should be in the parser, so as to avoid falling into another CPP mistake. (Later): I'm sure there's actually good case for this. People who need that feature can use m4/cpp on top of Bison. I don't think it is worth the trouble in Bison itself. ** XML Output There are couple of available extensions of Bison targeting some XML output. Some day we should consider including them. One issue is that they seem to be quite orthogonal to the parsing technique, and seem to depend mostly on the possibility to have some code triggered for each reduction. As a matter of fact, such hooks could also be used to generate the yydebug traces. Some generic scheme probably exists in there. XML output for GNU Bison and gcc http://www.cs.may.ie/~jpower/Research/bisonXML/ XML output for GNU Bison http://yaxx.sourceforge.net/ * Coding system independence Paul notes: Currently Bison assumes 8-bit bytes (i.e. that UCHAR_MAX is 255). It also assumes that the 8-bit character encoding is the same for the invocation of 'bison' as it is for the invocation of 'cc', but this is not necessarily true when people run bison on an ASCII host and then use cc on an EBCDIC host. I don't think these topics are worth our time addressing (unless we find a gung-ho volunteer for EBCDIC or PDP-10 ports :-) but they should probably be documented somewhere. More importantly, Bison does not currently allow NUL bytes in tokens, either via escapes (e.g., "x\0y") or via a NUL byte in the source code. This should get fixed. * Broken options? ** %token-table ** Skeleton strategy Must we keep %token-table? * Precedence ** Partial order It is unfortunate that there is a total order for precedence. It makes it impossible to have modular precedence information. We should move to partial orders (sounds like series/parallel orders to me). This is a prerequisite for modules. * Pre and post actions. From: Florian Krohm <florian@edamail.fishkill.ibm.com> Subject: YYACT_EPILOGUE To: bug-bison@gnu.org X-Sent: 1 week, 4 days, 14 hours, 38 minutes, 11 seconds ago The other day I had the need for explicitly building the parse tree. I used %locations for that and defined YYLLOC_DEFAULT to call a function that returns the tree node for the production. Easy. But I also needed to assign the S-attribute to the tree node. That cannot be done in YYLLOC_DEFAULT, because it is invoked before the action is executed. The way I solved this was to define a macro YYACT_EPILOGUE that would be invoked after the action. For reasons of symmetry I also added YYACT_PROLOGUE. Although I had no use for that I can envision how it might come in handy for debugging purposes. All is needed is to add #if YYLSP_NEEDED YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen, yyloc, (yylsp - yylen)); #else YYACT_EPILOGUE (yyval, (yyvsp - yylen), yylen); #endif at the proper place to bison.simple. Ditto for YYACT_PROLOGUE. I was wondering what you think about adding YYACT_PROLOGUE/EPILOGUE to bison. If you're interested, I'll work on a patch. * Better graphics Equip the parser with a means to create the (visual) parse tree. ----- # LocalWords: Cex gnulib gl Bistromathic TokenKinds yylex enum YYEOF EOF # LocalWords: YYerror gettext af hb YYERRCODE undef calc FIXME dev yyerror # LocalWords: Autoconf YYUNDEFTOK lexemes parsers Bistromathic's yyreport # LocalWords: const argc yacc yyclearin lookahead destructor Rici incluent # LocalWords: yydestruct yydiscardin catégories d'avertissements sr activé # LocalWords: conflits défaut rr l'alias chaîne n'est attaché un symbole # LocalWords: obsolète règle vide midrule valeurs de intermédiaire ou avec # LocalWords: définies inutilisées priorité associativité inutiles POSIX # LocalWords: incompatibilités tous les autres avertissements sauf dans rp # LocalWords: désactiver CATEGORIE traiter comme des erreurs glr Akim bool # LocalWords: Demaille arith lalr goto struct pathlen nullable ntokens lr # LocalWords: nterm bitsetv ielr ritem nstates nrules nritems yysymbol EQ # LocalWords: SymbolKind YYEMPTY YYUNDEF YYTNAME NUM yyntokens yytname sed # LocalWords: nonterminals yykind yycode YYNAMES yynames init getName conv # LocalWords: TokenKind semanticVal ival yychar yylval yylexer Tolmer hoc # LocalWords: Sobisch YYPTRDIFF ptrdiff Autotest YYPRINT toknum yytoknum # LocalWords: sym Wother stderr FP fixits xgettext fdiagnostics Graphviz # LocalWords: graphviz VCG bitset xml bw maint yytoken YYABORT deps # LocalWords: YYACCEPT yytranslate nonnegative destructors yyerrlab repo # LocalWords: backends stmt expr yy Mardle baz qux Vadim Maslow CPP cpp # LocalWords: yydebug gcc UCHAR EBCDIC gung PDP NUL Pre Florian Krohm utf # LocalWords: YYACT YYLLOC YYLSP yyval yyvsp yylen yyloc yylsp endif # LocalWords: ispell american Local Variables: mode: outline coding: utf-8 fill-column: 76 ispell-dictionary: "american" End: Copyright (C) 2001-2004, 2006, 2008-2015, 2018-2020 Free Software Foundation, Inc. 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