On Sun, 5 Aug 2007, Hans Aberg wrote: > When I tried it, it worked: > $ bison parser.y++ > parser.y++: conflicts: 455 shift/reduce, 1 reduce/reduce
I never upload non-working versions. If I have a similar question again, I'll upload examples to an ftp server. Sorry for the inconvenience this time. > So then it hard for anyone but yourself to fix the problem. If you are sure it > is a bug, report it to Bison Bugs <[EMAIL PROTECTED]>. Be sure to include > relevant data. No, I'm sure it's not a bug in Bison, just something Bison's not meant or equipped to handle, or me trying to use Bison in a way it's not meant to be used. > It is your grammar, but I think it will be unmanageable. Well, it's not completely mine. It's based on the grammar of Metafont, written by Donald Knuth. However, he implemented his parser from scratch in Pascal. I used his description of the grammar in Backus-Naur as the basis of the rules I've written in Bison. However, Metafont doesn't define that many types or operations, so my grammar has become much larger than the grammar of Metafont. I've also made some changes because of the way Bison works. While it is somewhat large and complex, many of the rules fall into patterns that are repeated over and over for the various types. I have a pretty good overview of it, having written every line of it. I'm sure it would be difficult for someone else to understand, coming to it now, without having read it when it was smaller and simpler. I think a knowledge of the rules of the Metafont grammar would be nearly indispensable. It's a moot point, however, since no one has ever expressed an interest in understanding it. The problem (if it is a problem) with the shift/reduce conflicts appeared very early on. The correct resolution is always to shift, so I didn't worry about it, unless a rule caused a large increase in the number of s/r conflicts. I didn't think that it caused extra work for Bison or that they needed to be kept track of. If they do, I may have problems that will probably not be so easy to solve. > The Bison has a > suggestion for fixing reduce/reduce conflicts. In, some cases, when it can't > be resolve compile time, one may have to use GLR (%glr). I'll have to look this up, but I think there may have been some issue with using GLR. If the `yyparse' generated when using this option isn't thread-safe, I won't be able to use it. There is only one reduce/reduce conflict. I don't remember the details, since I wrote those rules so long ago, but it has to with the syntax for defining a `path' using `points' and "connectors", i.e., something very basic to a Metafont-like language. I determined at the time after a lot of fiddling that I couldn't do anything about it, but that the parser behaved the way I wanted it to. > I think there is an > example of how to do that with C++. But one has been able to make a LALR(1) > for C++, too. I'm not sure whether this is relevant, but I only use C++ in the actions; Bison generates the regular C version of `yyparse'. > So it is a question of style. Even if a language has given > grammar, it may not be adapted for a parser general. So rewriting it > is normal implementing. I'm sure you're right, and it's always been a matter of compromise. I've been getting very good results with Bison for the 6 years I've been working on this project. I simply don't have the knowledge to write a parser from scratch, and I doubt that I would want to implement one the way Knuth did in the 1980's using Pascal, even if I had the leisure to read through his code. I'm sure he did it very well, but that's not the point. If I had invented the grammar from scratch, I surely would have tried to avoid all shift/reduce conflicts. However, they seem to be inherent in Knuth's rules, when one tries to implement them using Bison. I just tried getting rid of all the `any_variable: <type>_variable' rules, but it didn't work: I got five fewer s/r conflicts but four additional r/r conflicts, and input that previously worked caused an error at run-time. That is, it caused an error in one of my functions, not an error affecting the run environment. Obviously, this will require some thorough investigation. I don't really think that my grammar needs a major rewrite, even if I had the time for something like that. I will try to get rid of any unnecessary rules and simplify the grammar wherever I can. I had already determined that it works better to have more rules that are simpler instead of fewer rules that are more complicated. In case anyone wants to try running the program, there's an option for outputting the debugging output produced by Bison, namely `--bison-trace' (can be abbreviated to `-bi'). I've put an example in the attached file `ttemp.txt'. Thanks again, Laurence
(Enter:) 3dldf --bison-trace --silent (Output:) 3dldf -bi -si Starting parse Entering state 0 Reducing stack by rule 2 (line 5394), -> statement_list Stack now 0 Entering state 2 Reading a token: * (Enter:) point p; p := (1, 2, 3); end; (Output:) 3dldf --bison-trace --silent Starting parse Entering state 0 Reducing stack by rule 2 (line 5394), -> statement_list Stack now 0 Entering state 2 Reading a token: * point p; p := (1, 2, 3); end; Next token is token POINT_DECLARATOR () Shifting token POINT_DECLARATOR, Entering state 23 Reading a token: Next token is token SYMBOL_0 () Shifting token SYMBOL_0, Entering state 5 Reducing stack by rule 2016 (line 91024), SYMBOL_0 -> tag Stack now 0 2 23 Entering state 453 Reducing stack by rule 1998 (line 89385), tag -> symbolic_token Stack now 0 2 23 Entering state 451 Reducing stack by rule 2024 (line 91730), -> declared_suffix Stack now 0 2 23 451 Entering state 1515 Reading a token: Next token is token SEMI_COLON () Reducing stack by rule 1918 (line 83313), symbolic_token declared_suffix -> declared_variable Stack now 0 2 23 Entering state 450 Reducing stack by rule 1916 (line 83120), declared_variable -> declaration_list Stack now 0 2 23 Entering state 463 Next token is token SEMI_COLON () Reducing stack by rule 1850 (line 77380), POINT_DECLARATOR declaration_list -> point_declaration Stack now 0 2 Entering state 363 Reducing stack by rule 1773 (line 75230), point_declaration -> declaration Stack now 0 2 Entering state 351 Next token is token SEMI_COLON () Shifting token SEMI_COLON, Entering state 1512 Reducing stack by rule 6 (line 5903), declaration SEMI_COLON -> statement Stack now 0 2 Entering state 166 Reducing stack by rule 3 (line 5401), statement_list statement -> statement_list Stack now 0 Entering state 2 Reading a token: Next token is token SYMBOL_0 () Shifting token SYMBOL_0, Entering state 5 Reducing stack by rule 2016 (line 91024), SYMBOL_0 -> tag Stack now 0 2 Entering state 429 Reducing stack by rule 235 (line 20534), -> suffix Stack now 0 2 429 Entering state 1513 Reading a token: Next token is token ASSIGN () Reducing stack by rule 234 (line 20513), tag suffix -> variable Stack now 0 2 Entering state 227 Reading a token: Next token is token POINT () Shifting token POINT, Entering state 1276 Reducing stack by rule 328 (line 22070), variable POINT -> point_variable Stack now 0 2 Entering state 276 Reading a token: Next token is token ASSIGN () Shifting token ASSIGN, Entering state 1419 Reading a token: Next token is token LEFT_PARENTHESIS () Shifting token LEFT_PARENTHESIS, Entering state 1490 Reading a token: Next token is token INTEGER () Shifting token INTEGER, Entering state 591 Reducing stack by rule 1108 (line 43300), INTEGER -> numeric_token Stack now 0 2 276 1419 1490 Entering state 668 Reading a token: Next token is token COMMA () Reducing stack by rule 990 (line 40528), numeric_token -> numeric_token_atom Stack now 0 2 276 1419 1490 Entering state 661 Reducing stack by rule 987 (line 40361), numeric_token_atom -> numeric_atom Stack now 0 2 276 1419 1490 Entering state 660 Next token is token COMMA () Reducing stack by rule 991 (line 40539), numeric_atom -> numeric_primary Stack now 0 2 276 1419 1490 Entering state 662 Reducing stack by rule 1081 (line 42246), numeric_primary -> numeric_secondary Stack now 0 2 276 1419 1490 Entering state 1234 Next token is token COMMA () Reducing stack by rule 1101 (line 42981), numeric_secondary -> numeric_tertiary Stack now 0 2 276 1419 1490 Entering state 975 Next token is token COMMA () Reducing stack by rule 1107 (line 43275), numeric_tertiary -> numeric_expression Stack now 0 2 276 1419 1490 Entering state 1813 Next token is token COMMA () Shifting token COMMA, Entering state 2482 Reading a token: Next token is token INTEGER () Shifting token INTEGER, Entering state 591 Reducing stack by rule 1108 (line 43300), INTEGER -> numeric_token Stack now 0 2 276 1419 1490 1813 2482 Entering state 668 Reading a token: Next token is token COMMA () Reducing stack by rule 990 (line 40528), numeric_token -> numeric_token_atom Stack now 0 2 276 1419 1490 1813 2482 Entering state 661 Reducing stack by rule 987 (line 40361), numeric_token_atom -> numeric_atom Stack now 0 2 276 1419 1490 1813 2482 Entering state 660 Next token is token COMMA () Reducing stack by rule 991 (line 40539), numeric_atom -> numeric_primary Stack now 0 2 276 1419 1490 1813 2482 Entering state 662 Reducing stack by rule 1081 (line 42246), numeric_primary -> numeric_secondary Stack now 0 2 276 1419 1490 1813 2482 Entering state 1234 Next token is token COMMA () Reducing stack by rule 1101 (line 42981), numeric_secondary -> numeric_tertiary Stack now 0 2 276 1419 1490 1813 2482 Entering state 975 Next token is token COMMA () Reducing stack by rule 1107 (line 43275), numeric_tertiary -> numeric_expression Stack now 0 2 276 1419 1490 1813 2482 Entering state 3028 Reducing stack by rule 1112 (line 43398), numeric_expression COMMA numeric_expression -> numeric_sublist Stack now 0 2 276 1419 1490 Entering state 1523 Next token is token COMMA () Shifting token COMMA, Entering state 2484 Reading a token: Next token is token INTEGER () Shifting token INTEGER, Entering state 591 Reducing stack by rule 1108 (line 43300), INTEGER -> numeric_token Stack now 0 2 276 1419 1490 1523 2484 Entering state 668 Reading a token: Next token is token RIGHT_PARENTHESIS () Reducing stack by rule 990 (line 40528), numeric_token -> numeric_token_atom Stack now 0 2 276 1419 1490 1523 2484 Entering state 661 Reducing stack by rule 987 (line 40361), numeric_token_atom -> numeric_atom Stack now 0 2 276 1419 1490 1523 2484 Entering state 660 Next token is token RIGHT_PARENTHESIS () Reducing stack by rule 991 (line 40539), numeric_atom -> numeric_primary Stack now 0 2 276 1419 1490 1523 2484 Entering state 662 Reducing stack by rule 1081 (line 42246), numeric_primary -> numeric_secondary Stack now 0 2 276 1419 1490 1523 2484 Entering state 1234 Next token is token RIGHT_PARENTHESIS () Reducing stack by rule 1101 (line 42981), numeric_secondary -> numeric_tertiary Stack now 0 2 276 1419 1490 1523 2484 Entering state 975 Next token is token RIGHT_PARENTHESIS () Reducing stack by rule 1107 (line 43275), numeric_tertiary -> numeric_expression Stack now 0 2 276 1419 1490 1523 2484 Entering state 3029 Reducing stack by rule 1113 (line 43414), numeric_sublist COMMA numeric_expression -> numeric_sublist Stack now 0 2 276 1419 1490 Entering state 1523 Next token is token RIGHT_PARENTHESIS () Shifting token RIGHT_PARENTHESIS, Entering state 2485 Reducing stack by rule 1111 (line 43369), LEFT_PARENTHESIS numeric_sublist RIGHT_PARENTHESIS -> numeric_list Stack now 0 2 276 1419 Entering state 670 Reducing stack by rule 1197 (line 47368), numeric_list -> point_primary Stack now 0 2 276 1419 Entering state 671 Reading a token: Next token is token SEMI_COLON () Reducing stack by rule 1265 (line 49180), point_primary -> point_secondary Stack now 0 2 276 1419 Entering state 672 Next token is token SEMI_COLON () Reducing stack by rule 1275 (line 50175), point_secondary -> point_tertiary Stack now 0 2 276 1419 Entering state 673 Next token is token SEMI_COLON () Reducing stack by rule 1278 (line 50614), point_tertiary -> point_expression Stack now 0 2 276 1419 Entering state 2356 Reducing stack by rule 108 (line 8582), point_variable ASSIGN point_expression -> point_assignment Stack now 0 2 Entering state 182 Reducing stack by rule 39 (line 7397), point_assignment -> assignment Stack now 0 2 Entering state 168 Next token is token SEMI_COLON () Shifting token SEMI_COLON, Entering state 1263 Reducing stack by rule 7 (line 6004), assignment SEMI_COLON -> statement Stack now 0 2 Entering state 166 Reducing stack by rule 3 (line 5401), statement_list statement -> statement_list Stack now 0 Entering state 2 Reading a token: Next token is token END () Shifting token END, Entering state 118 Reducing stack by rule 1 (line 5210), statement_list END -> program
_______________________________________________ help-bison@gnu.org http://lists.gnu.org/mailman/listinfo/help-bison
