--- /dev/null
+======================================================================\r
+\r
+ CHANGES_SUMMARY.TXT\r
+\r
+ A QUICK overview of changes from 1.33 in reverse order\r
+\r
+ A summary of additions rather than bug fixes and minor code changes.\r
+\r
+ Numbers refer to items in CHANGES_FROM_133*.TXT\r
+ which may contain additional information.\r
+\r
+ DISCLAIMER\r
+\r
+ The software and these notes are provided "as is". They may include\r
+ typographical or technical errors and their authors disclaims all\r
+ liability of any kind or nature for damages due to error, fault,\r
+ defect, or deficiency regardless of cause. All warranties of any\r
+ kind, either express or implied, including, but not limited to, the\r
+ implied warranties of merchantability and fitness for a particular\r
+ purpose are disclaimed.\r
+\r
+======================================================================\r
+\r
+#258. You can specify a user-defined base class for your parser\r
+\r
+ The base class must constructor must have a signature similar to\r
+ that of ANTLRParser.\r
+\r
+#253. Generation of block preamble (-preamble and -preamble_first)\r
+\r
+ The antlr option -preamble causes antlr to insert the code\r
+ BLOCK_PREAMBLE at the start of each rule and block.\r
+\r
+ The antlr option -preamble_first is similar, but inserts the\r
+ code BLOCK_PREAMBLE_FIRST(PreambleFirst_123) where the symbol\r
+ PreambleFirst_123 is equivalent to the first set defined by\r
+ the #FirstSetSymbol described in Item #248.\r
+\r
+#248. Generate symbol for first set of an alternative\r
+\r
+ rr : #FirstSetSymbol(rr_FirstSet) ( Foo | Bar ) ;\r
+\r
+#216. Defer token fetch for C++ mode\r
+\r
+ When the ANTLRParser class is built with the pre-processor option \r
+ ZZDEFER_FETCH defined, the fetch of new tokens by consume() is deferred\r
+ until LA(i) or LT(i) is called. \r
+\r
+#215. Use reset() to reset DLGLexerBase\r
+#188. Added pccts/h/DLG_stream_input.h\r
+#180. Added ANTLRParser::getEofToken()\r
+#173. -glms for Microsoft style filenames with -gl\r
+#170. Suppression for predicates with lookahead depth >1\r
+\r
+ Consider the following grammar with -ck 2 and the predicate in rule\r
+ "a" with depth 2:\r
+\r
+ r1 : (ab)* "@"\r
+ ;\r
+\r
+ ab : a\r
+ | b\r
+ ;\r
+\r
+ a : (A B)? => <<p(LATEXT(2))>>? A B C\r
+ ;\r
+\r
+ b : A B C\r
+ ;\r
+\r
+ Normally, the predicate would be hoisted into rule r1 in order to\r
+ determine whether to call rule "ab". However it should *not* be\r
+ hoisted because, even if p is false, there is a valid alternative\r
+ in rule b. With "-mrhoistk on" the predicate will be suppressed.\r
+\r
+ If "-info p" command line option is present the following information\r
+ will appear in the generated code:\r
+\r
+ while ( (LA(1)==A)\r
+ #if 0\r
+\r
+ Part (or all) of predicate with depth > 1 suppressed by alternative\r
+ without predicate\r
+\r
+ pred << p(LATEXT(2))>>?\r
+ depth=k=2 ("=>" guard) rule a line 8 t1.g\r
+ tree context:\r
+ (root = A\r
+ B\r
+ )\r
+\r
+ The token sequence which is suppressed: ( A B )\r
+ The sequence of references which generate that sequence of tokens:\r
+\r
+ 1 to ab r1/1 line 1 t1.g\r
+ 2 ab ab/1 line 4 t1.g\r
+ 3 to b ab/2 line 5 t1.g\r
+ 4 b b/1 line 11 t1.g\r
+ 5 #token A b/1 line 11 t1.g\r
+ 6 #token B b/1 line 11 t1.g\r
+\r
+ #endif\r
+\r
+ A slightly more complicated example:\r
+\r
+ r1 : (ab)* "@"\r
+ ;\r
+\r
+ ab : a\r
+ | b\r
+ ;\r
+\r
+ a : (A B)? => <<p(LATEXT(2))>>? (A B | D E)\r
+ ;\r
+\r
+ b : <<q(LATEXT(2))>>? D E\r
+ ;\r
+\r
+\r
+ In this case, the sequence (D E) in rule "a" which lies behind\r
+ the guard is used to suppress the predicate with context (D E)\r
+ in rule b.\r
+\r
+ while ( (LA(1)==A || LA(1)==D)\r
+ #if 0\r
+\r
+ Part (or all) of predicate with depth > 1 suppressed by alternative\r
+ without predicate\r
+\r
+ pred << q(LATEXT(2))>>?\r
+ depth=k=2 rule b line 11 t2.g\r
+ tree context:\r
+ (root = D\r
+ E\r
+ )\r
+\r
+ The token sequence which is suppressed: ( D E )\r
+ The sequence of references which generate that sequence of tokens:\r
+\r
+ 1 to ab r1/1 line 1 t2.g\r
+ 2 ab ab/1 line 4 t2.g\r
+ 3 to a ab/1 line 4 t2.g\r
+ 4 a a/1 line 8 t2.g\r
+ 5 #token D a/1 line 8 t2.g\r
+ 6 #token E a/1 line 8 t2.g\r
+\r
+ #endif\r
+ &&\r
+ #if 0\r
+\r
+ pred << p(LATEXT(2))>>?\r
+ depth=k=2 ("=>" guard) rule a line 8 t2.g\r
+ tree context:\r
+ (root = A\r
+ B\r
+ )\r
+\r
+ #endif\r
+\r
+ (! ( LA(1)==A && LA(2)==B ) || p(LATEXT(2)) ) {\r
+ ab();\r
+ ...\r
+\r
+#165. (Changed in MR13) option -newAST\r
+\r
+ To create ASTs from an ANTLRTokenPtr antlr usually calls\r
+ "new AST(ANTLRTokenPtr)". This option generates a call\r
+ to "newAST(ANTLRTokenPtr)" instead. This allows a user\r
+ to define a parser member function to create an AST object.\r
+\r
+#161. (Changed in MR13) Switch -gxt inhibits generation of tokens.h\r
+\r
+#158. (Changed in MR13) #header causes problem for pre-processors\r
+\r
+ A user who runs the C pre-processor on antlr source suggested\r
+ that another syntax be allowed. With MR13 such directives\r
+ such as #header, #pragma, etc. may be written as "\#header",\r
+ "\#pragma", etc. For escaping pre-processor directives inside\r
+ a #header use something like the following:\r
+\r
+ \#header\r
+ <<\r
+ \#include <stdio.h>\r
+ >>\r
+\r
+#155. (Changed in MR13) Context behind predicates can suppress\r
+\r
+ With -mrhoist enabled the context behind a guarded predicate can\r
+ be used to suppress other predicates. Consider the following grammar:\r
+\r
+ r0 : (r1)+;\r
+\r
+ r1 : rp\r
+ | rq\r
+ ;\r
+ rp : <<p LATEXT(1)>>? B ;\r
+ rq : (A)? => <<q LATEXT(1)>>? (A|B);\r
+\r
+ In earlier versions both predicates "p" and "q" would be hoisted into\r
+ rule r0. With MR12c predicate p is suppressed because the context which\r
+ follows predicate q includes "B" which can "cover" predicate "p". In\r
+ other words, in trying to decide in r0 whether to call r1, it doesn't\r
+ really matter whether p is false or true because, either way, there is\r
+ a valid choice within r1.\r
+\r
+#154. (Changed in MR13) Making hoist suppression explicit using <<nohoist>>\r
+\r
+ A common error, even among experienced pccts users, is to code\r
+ an init-action to inhibit hoisting rather than a leading action.\r
+ An init-action does not inhibit hoisting.\r
+\r
+ This was coded:\r
+\r
+ rule1 : <<;>> rule2\r
+\r
+ This is what was meant:\r
+\r
+ rule1 : <<;>> <<;>> rule2\r
+\r
+ With MR13, the user can code:\r
+\r
+ rule1 : <<;>> <<nohoist>> rule2\r
+\r
+ The following will give an error message:\r
+\r
+ rule1 : <<nohoist>> rule2\r
+\r
+ If the <<nohoist>> appears as an init-action rather than a leading\r
+ action an error message is issued. The meaning of an init-action\r
+ containing "nohoist" is unclear: does it apply to just one\r
+ alternative or to all alternatives ?\r
+\r
+#151a. Addition of ANTLRParser::getLexer(), ANTLRTokenStream::getLexer()\r
+\r
+ You must manually cast the ANTLRTokenStream to your program's\r
+ lexer class. Because the name of the lexer's class is not fixed.\r
+ Thus it is impossible to incorporate it into the DLGLexerBase\r
+ class.\r
+\r
+#151b.(Changed in MR12) ParserBlackBox member getLexer()\r
+\r
+#150. (Changed in MR12) syntaxErrCount and lexErrCount now public\r
+\r
+#149. (Changed in MR12) antlr option -info o (letter o for orphan)\r
+\r
+ If there is more than one rule which is not referenced by any\r
+ other rule then all such rules are listed. This is useful for\r
+ alerting one to rules which are not used, but which can still\r
+ contribute to ambiguity.\r
+\r
+#148. (Changed in MR11) #token names appearing in zztokens,token_tbl\r
+\r
+ One can write:\r
+\r
+ #token Plus ("+") "\+"\r
+ #token RP ("(") "\("\r
+ #token COM ("comment begin") "/\*"\r
+\r
+ The string in parenthesis will be used in syntax error messages.\r
+\r
+#146. (Changed in MR11) Option -treport for locating "difficult" alts\r
+\r
+ It can be difficult to determine which alternatives are causing\r
+ pccts to work hard to resolve an ambiguity. In some cases the\r
+ ambiguity is successfully resolved after much CPU time so there\r
+ is no message at all.\r
+\r
+ A rough measure of the amount of work being peformed which is\r
+ independent of the CPU speed and system load is the number of\r
+ tnodes created. Using "-info t" gives information about the\r
+ total number of tnodes created and the peak number of tnodes.\r
+\r
+ Tree Nodes: peak 1300k created 1416k lost 0\r
+\r
+ It also puts in the generated C or C++ file the number of tnodes\r
+ created for a rule (at the end of the rule). However this\r
+ information is not sufficient to locate the alternatives within\r
+ a rule which are causing the creation of tnodes.\r
+\r
+ Using:\r
+\r
+ antlr -treport 100000 ....\r
+\r
+ causes antlr to list on stdout any alternatives which require the\r
+ creation of more than 100,000 tnodes, along with the lookahead sets\r
+ for those alternatives.\r
+\r
+ The following is a trivial case from the ansi.g grammar which shows\r
+ the format of the report. This report might be of more interest\r
+ in cases where 1,000,000 tuples were created to resolve the ambiguity.\r
+\r
+ -------------------------------------------------------------------------\r
+ There were 0 tuples whose ambiguity could not be resolved\r
+ by full lookahead\r
+ There were 157 tnodes created to resolve ambiguity between:\r
+\r
+ Choice 1: statement/2 line 475 file ansi.g\r
+ Choice 2: statement/3 line 476 file ansi.g\r
+\r
+ Intersection of lookahead[1] sets:\r
+\r
+ IDENTIFIER\r
+\r
+ Intersection of lookahead[2] sets:\r
+\r
+ LPARENTHESIS COLON AMPERSAND MINUS\r
+ STAR PLUSPLUS MINUSMINUS ONESCOMPLEMENT\r
+ NOT SIZEOF OCTALINT DECIMALINT\r
+ HEXADECIMALINT FLOATONE FLOATTWO IDENTIFIER\r
+ STRING CHARACTER\r
+ -------------------------------------------------------------------------\r
+\r
+#143. (Changed in MR11) Optional ";" at end of #token statement\r
+\r
+ Fixes problem of:\r
+\r
+ #token X "x"\r
+\r
+ <<\r
+ parser action\r
+ >>\r
+\r
+ Being confused with:\r
+\r
+ #token X "x" <<lexical action>>\r
+\r
+#142. (Changed in MR11) class BufFileInput subclass of DLGInputStream\r
+\r
+ Alexey Demakov (demakov@kazbek.ispras.ru) has supplied class\r
+ BufFileInput derived from DLGInputStream which provides a\r
+ function lookahead(char *string) to test characters in the\r
+ input stream more than one character ahead.\r
+ The class is located in pccts/h/BufFileInput.* of the kit.\r
+\r
+#140. #pred to define predicates\r
+\r
+ +---------------------------------------------------+\r
+ | Note: Assume "-prc on" for this entire discussion |\r
+ +---------------------------------------------------+\r
+\r
+ A problem with predicates is that each one is regarded as\r
+ unique and capable of disambiguating cases where two\r
+ alternatives have identical lookahead. For example:\r
+\r
+ rule : <<pred(LATEXT(1))>>? A\r
+ | <<pred(LATEXT(1))>>? A\r
+ ;\r
+\r
+ will not cause any error messages or warnings to be issued\r
+ by earlier versions of pccts. To compare the text of the\r
+ predicates is an incomplete solution.\r
+\r
+ In 1.33MR11 I am introducing the #pred statement in order to\r
+ solve some problems with predicates. The #pred statement allows\r
+ one to give a symbolic name to a "predicate literal" or a\r
+ "predicate expression" in order to refer to it in other predicate\r
+ expressions or in the rules of the grammar.\r
+\r
+ The predicate literal associated with a predicate symbol is C\r
+ or C++ code which can be used to test the condition. A\r
+ predicate expression defines a predicate symbol in terms of other\r
+ predicate symbols using "!", "&&", and "||". A predicate symbol\r
+ can be defined in terms of a predicate literal, a predicate\r
+ expression, or *both*.\r
+\r
+ When a predicate symbol is defined with both a predicate literal\r
+ and a predicate expression, the predicate literal is used to generate\r
+ code, but the predicate expression is used to check for two\r
+ alternatives with identical predicates in both alternatives.\r
+\r
+ Here are some examples of #pred statements:\r
+\r
+ #pred IsLabel <<isLabel(LATEXT(1))>>?\r
+ #pred IsLocalVar <<isLocalVar(LATEXT(1))>>?\r
+ #pred IsGlobalVar <<isGlobalVar(LATEXT(1)>>?\r
+ #pred IsVar <<isVar(LATEXT(1))>>? IsLocalVar || IsGlobalVar\r
+ #pred IsScoped <<isScoped(LATEXT(1))>>? IsLabel || IsLocalVar\r
+\r
+ I hope that the use of EBNF notation to describe the syntax of the\r
+ #pred statement will not cause problems for my readers (joke).\r
+\r
+ predStatement : "#pred"\r
+ CapitalizedName\r
+ (\r
+ "<<predicate_literal>>?"\r
+ | "<<predicate_literal>>?" predOrExpr\r
+ | predOrExpr\r
+ )\r
+ ;\r
+\r
+ predOrExpr : predAndExpr ( "||" predAndExpr ) * ;\r
+\r
+ predAndExpr : predPrimary ( "&&" predPrimary ) * ;\r
+\r
+ predPrimary : CapitalizedName\r
+ | "!" predPrimary\r
+ | "(" predOrExpr ")"\r
+ ;\r
+\r
+ What is the purpose of this nonsense ?\r
+\r
+ To understand how predicate symbols help, you need to realize that\r
+ predicate symbols are used in two different ways with two different\r
+ goals.\r
+\r
+ a. Allow simplification of predicates which have been combined\r
+ during predicate hoisting.\r
+\r
+ b. Allow recognition of identical predicates which can't disambiguate\r
+ alternatives with common lookahead.\r
+\r
+ First we will discuss goal (a). Consider the following rule:\r
+\r
+ rule0: rule1\r
+ | ID\r
+ | ...\r
+ ;\r
+\r
+ rule1: rule2\r
+ | rule3\r
+ ;\r
+\r
+ rule2: <<isX(LATEXT(1))>>? ID ;\r
+ rule3: <<!isX(LATEXT(1)>>? ID ;\r
+\r
+ When the predicates in rule2 and rule3 are combined by hoisting\r
+ to create a prediction expression for rule1 the result is:\r
+\r
+ if ( LA(1)==ID\r
+ && ( isX(LATEXT(1) || !isX(LATEXT(1) ) ) { rule1(); ...\r
+\r
+ This is inefficient, but more importantly, can lead to false\r
+ assumptions that the predicate expression distinguishes the rule1\r
+ alternative with some other alternative with lookahead ID. In\r
+ MR11 one can write:\r
+\r
+ #pred IsX <<isX(LATEXT(1))>>?\r
+\r
+ ...\r
+\r
+ rule2: <<IsX>>? ID ;\r
+ rule3: <<!IsX>>? ID ;\r
+\r
+ During hoisting MR11 recognizes this as a special case and\r
+ eliminates the predicates. The result is a prediction\r
+ expression like the following:\r
+\r
+ if ( LA(1)==ID ) { rule1(); ...\r
+\r
+ Please note that the following cases which appear to be equivalent\r
+ *cannot* be simplified by MR11 during hoisting because the hoisting\r
+ logic only checks for a "!" in the predicate action, not in the\r
+ predicate expression for a predicate symbol.\r
+\r
+ *Not* equivalent and is not simplified during hoisting:\r
+\r
+ #pred IsX <<isX(LATEXT(1))>>?\r
+ #pred NotX <<!isX(LATEXT(1))>>?\r
+ ...\r
+ rule2: <<IsX>>? ID ;\r
+ rule3: <<NotX>>? ID ;\r
+\r
+ *Not* equivalent and is not simplified during hoisting:\r
+\r
+ #pred IsX <<isX(LATEXT(1))>>?\r
+ #pred NotX !IsX\r
+ ...\r
+ rule2: <<IsX>>? ID ;\r
+ rule3: <<NotX>>? ID ;\r
+\r
+ Now we will discuss goal (b).\r
+\r
+ When antlr discovers that there is a lookahead ambiguity between\r
+ two alternatives it attempts to resolve the ambiguity by searching\r
+ for predicates in both alternatives. In the past any predicate\r
+ would do, even if the same one appeared in both alternatives:\r
+\r
+ rule: <<p(LATEXT(1))>>? X\r
+ | <<p(LATEXT(1))>>? X\r
+ ;\r
+\r
+ The #pred statement is a start towards solving this problem.\r
+ During ambiguity resolution (*not* predicate hoisting) the\r
+ predicates for the two alternatives are expanded and compared.\r
+ Consider the following example:\r
+\r
+ #pred Upper <<isUpper(LATEXT(1))>>?\r
+ #pred Lower <<isLower(LATEXT(1))>>?\r
+ #pred Alpha <<isAlpha(LATEXT(1))>>? Upper || Lower\r
+\r
+ rule0: rule1\r
+ | <<Alpha>>? ID\r
+ ;\r
+\r
+ rule1:\r
+ | rule2\r
+ | rule3\r
+ ...\r
+ ;\r
+\r
+ rule2: <<Upper>>? ID;\r
+ rule3: <<Lower>>? ID;\r
+\r
+ The definition of #pred Alpha expresses:\r
+\r
+ a. to test the predicate use the C code "isAlpha(LATEXT(1))"\r
+\r
+ b. to analyze the predicate use the information that\r
+ Alpha is equivalent to the union of Upper and Lower,\r
+\r
+ During ambiguity resolution the definition of Alpha is expanded\r
+ into "Upper || Lower" and compared with the predicate in the other\r
+ alternative, which is also "Upper || Lower". Because they are\r
+ identical MR11 will report a problem.\r
+\r
+ -------------------------------------------------------------------------\r
+ t10.g, line 5: warning: the predicates used to disambiguate rule rule0\r
+ (file t10.g alt 1 line 5 and alt 2 line 6)\r
+ are identical when compared without context and may have no\r
+ resolving power for some lookahead sequences.\r
+ -------------------------------------------------------------------------\r
+\r
+ If you use the "-info p" option the output file will contain:\r
+\r
+ +----------------------------------------------------------------------+\r
+ |#if 0 |\r
+ | |\r
+ |The following predicates are identical when compared without |\r
+ | lookahead context information. For some ambiguous lookahead |\r
+ | sequences they may not have any power to resolve the ambiguity. |\r
+ | |\r
+ |Choice 1: rule0/1 alt 1 line 5 file t10.g |\r
+ | |\r
+ | The original predicate for choice 1 with available context |\r
+ | information: |\r
+ | |\r
+ | OR expr |\r
+ | |\r
+ | pred << Upper>>? |\r
+ | depth=k=1 rule rule2 line 14 t10.g |\r
+ | set context: |\r
+ | ID |\r
+ | |\r
+ | pred << Lower>>? |\r
+ | depth=k=1 rule rule3 line 15 t10.g |\r
+ | set context: |\r
+ | ID |\r
+ | |\r
+ | The predicate for choice 1 after expansion (but without context |\r
+ | information): |\r
+ | |\r
+ | OR expr |\r
+ | |\r
+ | pred << isUpper(LATEXT(1))>>? |\r
+ | depth=k=1 rule line 1 t10.g |\r
+ | |\r
+ | pred << isLower(LATEXT(1))>>? |\r
+ | depth=k=1 rule line 2 t10.g |\r
+ | |\r
+ | |\r
+ |Choice 2: rule0/2 alt 2 line 6 file t10.g |\r
+ | |\r
+ | The original predicate for choice 2 with available context |\r
+ | information: |\r
+ | |\r
+ | pred << Alpha>>? |\r
+ | depth=k=1 rule rule0 line 6 t10.g |\r
+ | set context: |\r
+ | ID |\r
+ | |\r
+ | The predicate for choice 2 after expansion (but without context |\r
+ | information): |\r
+ | |\r
+ | OR expr |\r
+ | |\r
+ | pred << isUpper(LATEXT(1))>>? |\r
+ | depth=k=1 rule line 1 t10.g |\r
+ | |\r
+ | pred << isLower(LATEXT(1))>>? |\r
+ | depth=k=1 rule line 2 t10.g |\r
+ | |\r
+ | |\r
+ |#endif |\r
+ +----------------------------------------------------------------------+\r
+\r
+ The comparison of the predicates for the two alternatives takes\r
+ place without context information, which means that in some cases\r
+ the predicates will be considered identical even though they operate\r
+ on disjoint lookahead sets. Consider:\r
+\r
+ #pred Alpha\r
+\r
+ rule1: <<Alpha>>? ID\r
+ | <<Alpha>>? Label\r
+ ;\r
+\r
+ Because the comparison of predicates takes place without context\r
+ these will be considered identical. The reason for comparing\r
+ without context is that otherwise it would be necessary to re-evaluate\r
+ the entire predicate expression for each possible lookahead sequence.\r
+ This would require more code to be written and more CPU time during\r
+ grammar analysis, and it is not yet clear whether anyone will even make\r
+ use of the new #pred facility.\r
+\r
+ A temporary workaround might be to use different #pred statements\r
+ for predicates you know have different context. This would avoid\r
+ extraneous warnings.\r
+\r
+ The above example might be termed a "false positive". Comparison\r
+ without context will also lead to "false negatives". Consider the\r
+ following example:\r
+\r
+ #pred Alpha\r
+ #pred Beta\r
+\r
+ rule1: <<Alpha>>? A\r
+ | rule2\r
+ ;\r
+\r
+ rule2: <<Alpha>>? A\r
+ | <<Beta>>? B\r
+ ;\r
+\r
+ The predicate used for alt 2 of rule1 is (Alpha || Beta). This\r
+ appears to be different than the predicate Alpha used for alt1.\r
+ However, the context of Beta is B. Thus when the lookahead is A\r
+ Beta will have no resolving power and Alpha will be used for both\r
+ alternatives. Using the same predicate for both alternatives isn't\r
+ very helpful, but this will not be detected with 1.33MR11.\r
+\r
+ To properly handle this the predicate expression would have to be\r
+ evaluated for each distinct lookahead context.\r
+\r
+ To determine whether two predicate expressions are identical is\r
+ difficult. The routine may fail to identify identical predicates.\r
+\r
+ The #pred feature also compares predicates to see if a choice between\r
+ alternatives which is resolved by a predicate which makes the second\r
+ choice unreachable. Consider the following example:\r
+\r
+ #pred A <<A(LATEXT(1)>>?\r
+ #pred B <<B(LATEXT(1)>>?\r
+ #pred A_or_B A || B\r
+\r
+ r : s\r
+ | t\r
+ ;\r
+ s : <<A_or_B>>? ID\r
+ ;\r
+ t : <<A>>? ID\r
+ ;\r
+\r
+ ----------------------------------------------------------------------------\r
+ t11.g, line 5: warning: the predicate used to disambiguate the\r
+ first choice of rule r\r
+ (file t11.g alt 1 line 5 and alt 2 line 6)\r
+ appears to "cover" the second predicate when compared without context.\r
+ The second predicate may have no resolving power for some lookahead\r
+ sequences.\r
+ ----------------------------------------------------------------------------\r
+\r
+#132. (Changed in 1.33MR11) Recognition of identical predicates in alts\r
+\r
+ Prior to 1.33MR11, there would be no ambiguity warning when the\r
+ very same predicate was used to disambiguate both alternatives:\r
+\r
+ test: ref B\r
+ | ref C\r
+ ;\r
+\r
+ ref : <<pred(LATEXT(1)>>? A\r
+\r
+ In 1.33MR11 this will cause the warning:\r
+\r
+ warning: the predicates used to disambiguate rule test\r
+ (file v98.g alt 1 line 1 and alt 2 line 2)\r
+ are identical and have no resolving power\r
+\r
+ ----------------- Note -----------------\r
+\r
+ This is different than the following case\r
+\r
+ test: <<pred(LATEXT(1))>>? A B\r
+ | <<pred(LATEXT(1)>>? A C\r
+ ;\r
+\r
+ In this case there are two distinct predicates\r
+ which have exactly the same text. In the first\r
+ example there are two references to the same\r
+ predicate. The problem represented by this\r
+ grammar will be addressed later.\r
+\r
+\r
+#127. (Changed in 1.33MR11)\r
+\r
+ Count Syntax Errors Count DLG Errors\r
+ ------------------- ----------------\r
+\r
+ C++ mode ANTLRParser:: DLGLexerBase::\r
+ syntaxErrCount lexErrCount\r
+ C mode zzSyntaxErrCount zzLexErrCount\r
+\r
+ The C mode variables are global and initialized to 0.\r
+ They are *not* reset to 0 automatically when antlr is\r
+ restarted.\r
+\r
+ The C++ mode variables are public. They are initialized\r
+ to 0 by the constructors. They are *not* reset to 0 by the\r
+ ANTLRParser::init() method.\r
+\r
+ Suggested by Reinier van den Born (reinier@vnet.ibm.com).\r
+\r
+#126. (Changed in 1.33MR11) Addition of #first <<...>>\r
+\r
+ The #first <<...>> inserts the specified text in the output\r
+ files before any other #include statements required by pccts.\r
+ The only things before the #first text are comments and\r
+ a #define ANTLR_VERSION.\r
+\r
+ Requested by and Esa Pulkkinen (esap@cs.tut.fi) and Alexin\r
+ Zoltan (alexin@inf.u-szeged.hu).\r
+\r
+#124. A Note on the New "&&" Style Guarded Predicates\r
+\r
+ I've been asked several times, "What is the difference between\r
+ the old "=>" style guard predicates and the new style "&&" guard\r
+ predicates, and how do you choose one over the other" ?\r
+\r
+ The main difference is that the "=>" does not apply the\r
+ predicate if the context guard doesn't match, whereas\r
+ the && form always does. What is the significance ?\r
+\r
+ If you have a predicate which is not on the "leading edge"\r
+ it is cannot be hoisted. Suppose you need a predicate that\r
+ looks at LA(2). You must introduce it manually. The\r
+ classic example is:\r
+\r
+ castExpr :\r
+ LP typeName RP\r
+ | ....\r
+ ;\r
+\r
+ typeName : <<isTypeName(LATEXT(1))>>? ID\r
+ | STRUCT ID\r
+ ;\r
+\r
+ The problem is that isTypeName() isn't on the leading edge\r
+ of typeName, so it won't be hoisted into castExpr to help\r
+ make a decision on which production to choose.\r
+\r
+ The *first* attempt to fix it is this:\r
+\r
+ castExpr :\r
+ <<isTypeName(LATEXT(2))>>?\r
+ LP typeName RP\r
+ | ....\r
+ ;\r
+\r
+ Unfortunately, this won't work because it ignores\r
+ the problem of STRUCT. The solution is to apply\r
+ isTypeName() in castExpr if LA(2) is an ID and\r
+ don't apply it when LA(2) is STRUCT:\r
+\r
+ castExpr :\r
+ (LP ID)? => <<isTypeName(LATEXT(2))>>?\r
+ LP typeName RP\r
+ | ....\r
+ ;\r
+\r
+ In conclusion, the "=>" style guarded predicate is\r
+ useful when:\r
+\r
+ a. the tokens required for the predicate\r
+ are not on the leading edge\r
+ b. there are alternatives in the expression\r
+ selected by the predicate for which the\r
+ predicate is inappropriate\r
+\r
+ If (b) were false, then one could use a simple\r
+ predicate (assuming "-prc on"):\r
+\r
+ castExpr :\r
+ <<isTypeName(LATEXT(2))>>?\r
+ LP typeName RP\r
+ | ....\r
+ ;\r
+\r
+ typeName : <<isTypeName(LATEXT(1))>>? ID\r
+ ;\r
+\r
+ So, when do you use the "&&" style guarded predicate ?\r
+\r
+ The new-style "&&" predicate should always be used with\r
+ predicate context. The context guard is in ADDITION to\r
+ the automatically computed context. Thus it useful for\r
+ predicates which depend on the token type for reasons\r
+ other than context.\r
+\r
+ The following example is contributed by Reinier van den Born\r
+ (reinier@vnet.ibm.com).\r
+\r
+ +-------------------------------------------------------------------------+\r
+ | This grammar has two ways to call functions: |\r
+ | |\r
+ | - a "standard" call syntax with parens and comma separated args |\r
+ | - a shell command like syntax (no parens and spacing separated args) |\r
+ | |\r
+ | The former also allows a variable to hold the name of the function, |\r
+ | the latter can also be used to call external commands. |\r
+ | |\r
+ | The grammar (simplified) looks like this: |\r
+ | |\r
+ | fun_call : ID "(" { expr ("," expr)* } ")" |\r
+ | /* ID is function name */ |\r
+ | | "@" ID "(" { expr ("," expr)* } ")" |\r
+ | /* ID is var containing fun name */ |\r
+ | ; |\r
+ | |\r
+ | command : ID expr* /* ID is function name */ |\r
+ | | path expr* /* path is external command name */ |\r
+ | ; |\r
+ | |\r
+ | path : ID /* left out slashes and such */ |\r
+ | | "@" ID /* ID is environment var */ |\r
+ | ; |\r
+ | |\r
+ | expr : .... |\r
+ | | "(" expr ")"; |\r
+ | |\r
+ | call : fun_call |\r
+ | | command |\r
+ | ; |\r
+ | |\r
+ | Obviously the call is wildly ambiguous. This is more or less how this |\r
+ | is to be resolved: |\r
+ | |\r
+ | A call begins with an ID or an @ followed by an ID. |\r
+ | |\r
+ | If it is an ID and if it is an ext. command name -> command |\r
+ | if followed by a paren -> fun_call |\r
+ | otherwise -> command |\r
+ | |\r
+ | If it is an @ and if the ID is a var name -> fun_call |\r
+ | otherwise -> command |\r
+ | |\r
+ | One can implement these rules quite neatly using && predicates: |\r
+ | |\r
+ | call : ("@" ID)? && <<isVarName(LT(2))>>? fun_call |\r
+ | | (ID)? && <<isExtCmdName>>? command |\r
+ | | (ID "(")? fun_call |\r
+ | | command |\r
+ | ; |\r
+ | |\r
+ | This can be done better, so it is not an ideal example, but it |\r
+ | conveys the principle. |\r
+ +-------------------------------------------------------------------------+\r
+\r
+#122. (Changed in 1.33MR11) Member functions to reset DLG in C++ mode\r
+\r
+ void DLGFileReset(FILE *f) { input = f; found_eof = 0; }\r
+ void DLGStringReset(DLGChar *s) { input = s; p = &input[0]; }\r
+\r
+ Supplied by R.A. Nelson (cowboy@VNET.IBM.COM)\r
+\r
+#119. (Changed in 1.33MR11) Ambiguity aid for grammars\r
+\r
+ The user can ask for additional information on ambiguities reported\r
+ by antlr to stdout. At the moment, only one ambiguity report can\r
+ be created in an antlr run.\r
+\r
+ This feature is enabled using the "-aa" (Ambiguity Aid) option.\r
+\r
+ The following options control the reporting of ambiguities:\r
+\r
+ -aa ruleName Selects reporting by name of rule\r
+ -aa lineNumber Selects reporting by line number\r
+ (file name not compared)\r
+\r
+ -aam Selects "multiple" reporting for a token\r
+ in the intersection set of the\r
+ alternatives.\r
+\r
+ For instance, the token ID may appear dozens\r
+ of times in various paths as the program\r
+ explores the rules which are reachable from\r
+ the point of an ambiguity. With option -aam\r
+ every possible path the search program\r
+ encounters is reported.\r
+\r
+ Without -aam only the first encounter is\r
+ reported. This may result in incomplete\r
+ information, but the information may be\r
+ sufficient and much shorter.\r
+\r
+ -aad depth Selects the depth of the search.\r
+ The default value is 1.\r
+\r
+ The number of paths to be searched, and the\r
+ size of the report can grow geometrically\r
+ with the -ck value if a full search for all\r
+ contributions to the source of the ambiguity\r
+ is explored.\r
+\r
+ The depth represents the number of tokens\r
+ in the lookahead set which are matched against\r
+ the set of ambiguous tokens. A depth of 1\r
+ means that the search stops when a lookahead\r
+ sequence of just one token is matched.\r
+\r
+ A k=1 ck=6 grammar might generate 5,000 items\r
+ in a report if a full depth 6 search is made\r
+ with the Ambiguity Aid. The source of the\r
+ problem may be in the first token and obscured\r
+ by the volume of data - I hesitate to call\r
+ it information.\r
+\r
+ When the user selects a depth > 1, the search\r
+ is first performed at depth=1 for both\r
+ alternatives, then depth=2 for both alternatives,\r
+ etc.\r
+\r
+ Sample output for rule grammar in antlr.g itself:\r
+\r
+ +---------------------------------------------------------------------+\r
+ | Ambiguity Aid |\r
+ | |\r
+ | Choice 1: grammar/70 line 632 file a.g |\r
+ | Choice 2: grammar/82 line 644 file a.g |\r
+ | |\r
+ | Intersection of lookahead[1] sets: |\r
+ | |\r
+ | "\}" "class" "#errclass" "#tokclass" |\r
+ | |\r
+ | Choice:1 Depth:1 Group:1 ("#errclass") |\r
+ | 1 in (...)* block grammar/70 line 632 a.g |\r
+ | 2 to error grammar/73 line 635 a.g |\r
+ | 3 error error/1 line 894 a.g |\r
+ | 4 #token "#errclass" error/2 line 895 a.g |\r
+ | |\r
+ | Choice:1 Depth:1 Group:2 ("#tokclass") |\r
+ | 2 to tclass grammar/74 line 636 a.g |\r
+ | 3 tclass tclass/1 line 937 a.g |\r
+ | 4 #token "#tokclass" tclass/2 line 938 a.g |\r
+ | |\r
+ | Choice:1 Depth:1 Group:3 ("class") |\r
+ | 2 to class_def grammar/75 line 637 a.g |\r
+ | 3 class_def class_def/1 line 669 a.g |\r
+ | 4 #token "class" class_def/3 line 671 a.g |\r
+ | |\r
+ | Choice:1 Depth:1 Group:4 ("\}") |\r
+ | 2 #token "\}" grammar/76 line 638 a.g |\r
+ | |\r
+ | Choice:2 Depth:1 Group:5 ("#errclass") |\r
+ | 1 in (...)* block grammar/83 line 645 a.g |\r
+ | 2 to error grammar/93 line 655 a.g |\r
+ | 3 error error/1 line 894 a.g |\r
+ | 4 #token "#errclass" error/2 line 895 a.g |\r
+ | |\r
+ | Choice:2 Depth:1 Group:6 ("#tokclass") |\r
+ | 2 to tclass grammar/94 line 656 a.g |\r
+ | 3 tclass tclass/1 line 937 a.g |\r
+ | 4 #token "#tokclass" tclass/2 line 938 a.g |\r
+ | |\r
+ | Choice:2 Depth:1 Group:7 ("class") |\r
+ | 2 to class_def grammar/95 line 657 a.g |\r
+ | 3 class_def class_def/1 line 669 a.g |\r
+ | 4 #token "class" class_def/3 line 671 a.g |\r
+ | |\r
+ | Choice:2 Depth:1 Group:8 ("\}") |\r
+ | 2 #token "\}" grammar/96 line 658 a.g |\r
+ +---------------------------------------------------------------------+\r
+\r
+ For a linear lookahead set ambiguity (where k=1 or for k>1 but\r
+ when all lookahead sets [i] with i<k all have degree one) the\r
+ reports appear in the following order:\r
+\r
+ for (depth=1 ; depth <= "-aad depth" ; depth++) {\r
+ for (alternative=1; alternative <=2 ; alternative++) {\r
+ while (matches-are-found) {\r
+ group++;\r
+ print-report\r
+ };\r
+ };\r
+ };\r
+\r
+ For reporting a k-tuple ambiguity, the reports appear in the\r
+ following order:\r
+\r
+ for (depth=1 ; depth <= "-aad depth" ; depth++) {\r
+ while (matches-are-found) {\r
+ for (alternative=1; alternative <=2 ; alternative++) {\r
+ group++;\r
+ print-report\r
+ };\r
+ };\r
+ };\r
+\r
+ This is because matches are generated in different ways for\r
+ linear lookahead and k-tuples.\r
+\r
+#117. (Changed in 1.33MR10) new EXPERIMENTAL predicate hoisting code\r
+\r
+ The hoisting of predicates into rules to create prediction\r
+ expressions is a problem in antlr. Consider the following\r
+ example (k=1 with -prc on):\r
+\r
+ start : (a)* "@" ;\r
+ a : b | c ;\r
+ b : <<isUpper(LATEXT(1))>>? A ;\r
+ c : A ;\r
+\r
+ Prior to 1.33MR10 the code generated for "start" would resemble:\r
+\r
+ while {\r
+ if (LA(1)==A &&\r
+ (!LA(1)==A || isUpper())) {\r
+ a();\r
+ }\r
+ };\r
+\r
+ This code is wrong because it makes rule "c" unreachable from\r
+ "start". The essence of the problem is that antlr fails to\r
+ recognize that there can be a valid alternative within "a" even\r
+ when the predicate <<isUpper(LATEXT(1))>>? is false.\r
+\r
+ In 1.33MR10 with -mrhoist the hoisting of the predicate into\r
+ "start" is suppressed because it recognizes that "c" can\r
+ cover all the cases where the predicate is false:\r
+\r
+ while {\r
+ if (LA(1)==A) {\r
+ a();\r
+ }\r
+ };\r
+\r
+ With the antlr "-info p" switch the user will receive information\r
+ about the predicate suppression in the generated file:\r
+\r
+ --------------------------------------------------------------\r
+ #if 0\r
+\r
+ Hoisting of predicate suppressed by alternative without predicate.\r
+ The alt without the predicate includes all cases where\r
+ the predicate is false.\r
+\r
+ WITH predicate: line 7 v1.g\r
+ WITHOUT predicate: line 7 v1.g\r
+\r
+ The context set for the predicate:\r
+\r
+ A\r
+\r
+ The lookahead set for the alt WITHOUT the semantic predicate:\r
+\r
+ A\r
+\r
+ The predicate:\r
+\r
+ pred << isUpper(LATEXT(1))>>?\r
+ depth=k=1 rule b line 9 v1.g\r
+ set context:\r
+ A\r
+ tree context: null\r
+\r
+ Chain of referenced rules:\r
+\r
+ #0 in rule start (line 5 v1.g) to rule a\r
+ #1 in rule a (line 7 v1.g)\r
+\r
+ #endif\r
+ --------------------------------------------------------------\r
+\r
+ A predicate can be suppressed by a combination of alternatives\r
+ which, taken together, cover a predicate:\r
+\r
+ start : (a)* "@" ;\r
+\r
+ a : b | ca | cb | cc ;\r
+\r
+ b : <<isUpper(LATEXT(1))>>? ( A | B | C ) ;\r
+\r
+ ca : A ;\r
+ cb : B ;\r
+ cc : C ;\r
+\r
+ Consider a more complex example in which "c" covers only part of\r
+ a predicate:\r
+\r
+ start : (a)* "@" ;\r
+\r
+ a : b\r
+ | c\r
+ ;\r
+\r
+ b : <<isUpper(LATEXT(1))>>?\r
+ ( A\r
+ | X\r
+ );\r
+\r
+ c : A\r
+ ;\r
+\r
+ Prior to 1.33MR10 the code generated for "start" would resemble:\r
+\r
+ while {\r
+ if ( (LA(1)==A || LA(1)==X) &&\r
+ (! (LA(1)==A || LA(1)==X) || isUpper()) {\r
+ a();\r
+ }\r
+ };\r
+\r
+ With 1.33MR10 and -mrhoist the predicate context is restricted to\r
+ the non-covered lookahead. The code resembles:\r
+\r
+ while {\r
+ if ( (LA(1)==A || LA(1)==X) &&\r
+ (! (LA(1)==X) || isUpper()) {\r
+ a();\r
+ }\r
+ };\r
+\r
+ With the antlr "-info p" switch the user will receive information\r
+ about the predicate restriction in the generated file:\r
+\r
+ --------------------------------------------------------------\r
+ #if 0\r
+\r
+ Restricting the context of a predicate because of overlap\r
+ in the lookahead set between the alternative with the\r
+ semantic predicate and one without\r
+ Without this restriction the alternative without the predicate\r
+ could not be reached when input matched the context of the\r
+ predicate and the predicate was false.\r
+\r
+ WITH predicate: line 11 v4.g\r
+ WITHOUT predicate: line 12 v4.g\r
+\r
+ The original context set for the predicate:\r
+\r
+ A X\r
+\r
+ The lookahead set for the alt WITHOUT the semantic predicate:\r
+\r
+ A\r
+\r
+ The intersection of the two sets\r
+\r
+ A\r
+\r
+ The original predicate:\r
+\r
+ pred << isUpper(LATEXT(1))>>?\r
+ depth=k=1 rule b line 15 v4.g\r
+ set context:\r
+ A X\r
+ tree context: null\r
+\r
+ The new (modified) form of the predicate:\r
+\r
+ pred << isUpper(LATEXT(1))>>?\r
+ depth=k=1 rule b line 15 v4.g\r
+ set context:\r
+ X\r
+ tree context: null\r
+\r
+ #endif\r
+ --------------------------------------------------------------\r
+\r
+ The bad news about -mrhoist:\r
+\r
+ (a) -mrhoist does not analyze predicates with lookahead\r
+ depth > 1.\r
+\r
+ (b) -mrhoist does not look past a guarded predicate to\r
+ find context which might cover other predicates.\r
+\r
+ For these cases you might want to use syntactic predicates.\r
+ When a semantic predicate fails during guess mode the guess\r
+ fails and the next alternative is tried.\r
+\r
+ Limitation (a) is illustrated by the following example:\r
+\r
+ start : (stmt)* EOF ;\r
+\r
+ stmt : cast\r
+ | expr\r
+ ;\r
+ cast : <<isTypename(LATEXT(2))>>? LP ID RP ;\r
+\r
+ expr : LP ID RP ;\r
+\r
+ This is not much different from the first example, except that\r
+ it requires two tokens of lookahead context to determine what\r
+ to do. This predicate is NOT suppressed because the current version\r
+ is unable to handle predicates with depth > 1.\r
+\r
+ A predicate can be combined with other predicates during hoisting.\r
+ In those cases the depth=1 predicates are still handled. Thus,\r
+ in the following example the isUpper() predicate will be suppressed\r
+ by line #4 when hoisted from "bizarre" into "start", but will still\r
+ be present in "bizarre" in order to predict "stmt".\r
+\r
+ start : (bizarre)* EOF ; // #1\r
+ // #2\r
+ bizarre : stmt // #3\r
+ | A // #4\r
+ ;\r
+\r
+ stmt : cast\r
+ | expr\r
+ ;\r
+\r
+ cast : <<isTypename(LATEXT(2))>>? LP ID RP ;\r
+\r
+ expr : LP ID RP ;\r
+ | <<isUpper(LATEXT(1))>>? A\r
+\r
+ Limitation (b) is illustrated by the following example of a\r
+ context guarded predicate:\r
+\r
+ rule : (A)? <<p>>? // #1\r
+ (A // #2\r
+ |B // #3\r
+ ) // #4\r
+ | <<q>> B // #5\r
+ ;\r
+\r
+ Recall that this means that when the lookahead is NOT A then\r
+ the predicate "p" is ignored and it attempts to match "A|B".\r
+ Ideally, the "B" at line #3 should suppress predicate "q".\r
+ However, the current version does not attempt to look past\r
+ the guard predicate to find context which might suppress other\r
+ predicates.\r
+\r
+ In some cases -mrhoist will lead to the reporting of ambiguities\r
+ which were not visible before:\r
+\r
+ start : (a)* "@";\r
+ a : bc | d;\r
+ bc : b | c ;\r
+\r
+ b : <<isUpper(LATEXT(1))>>? A;\r
+ c : A ;\r
+\r
+ d : A ;\r
+\r
+ In this case there is a true ambiguity in "a" between "bc" and "d"\r
+ which can both match "A". Without -mrhoist the predicate in "b"\r
+ is hoisted into "a" and there is no ambiguity reported. However,\r
+ with -mrhoist, the predicate in "b" is suppressed by "c" (as it\r
+ should be) making the ambiguity in "a" apparent.\r
+\r
+ The motivations for these changes were hoisting problems reported\r
+ by Reinier van den Born (reinier@vnet.ibm.com) and several others.\r
+\r
+#113. (Changed in 1.33MR10) new context guarded pred: (g)? && <<p>>? expr\r
+\r
+ The existing context guarded predicate:\r
+\r
+ rule : (guard)? => <<p>>? expr\r
+ | next_alternative\r
+ ;\r
+\r
+ generates code which resembles:\r
+\r
+ if (lookahead(expr) && (!guard || pred)) {\r
+ expr()\r
+ } else ....\r
+\r
+ This is not suitable for some applications because it allows\r
+ expr() to be invoked when the predicate is false. This is\r
+ intentional because it is meant to mimic automatically computed\r
+ predicate context.\r
+\r
+ The new context guarded predicate uses the guard information\r
+ differently because it has a different goal. Consider:\r
+\r
+ rule : (guard)? && <<p>>? expr\r
+ | next_alternative\r
+ ;\r
+\r
+ The new style of context guarded predicate is equivalent to:\r
+\r
+ rule : <<guard==true && pred>>? expr\r
+ | next_alternative\r
+ ;\r
+\r
+ It generates code which resembles:\r
+\r
+ if (lookahead(expr) && guard && pred) {\r
+ expr();\r
+ } else ...\r
+\r
+ Both forms of guarded predicates severely restrict the form of\r
+ the context guard: it can contain no rule references, no\r
+ (...)*, no (...)+, and no {...}. It may contain token and\r
+ token class references, and alternation ("|").\r
+\r
+ Addition for 1.33MR11: in the token expression all tokens must\r
+ be at the same height of the token tree:\r
+\r
+ (A ( B | C))? && ... is ok (all height 2)\r
+ (A ( B | ))? && ... is not ok (some 1, some 2)\r
+ (A B C D | E F G H)? && ... is ok (all height 4)\r
+ (A B C D | E )? && ... is not ok (some 4, some 1)\r
+\r
+ This restriction is required in order to properly compute the lookahead\r
+ set for expressions like:\r
+\r
+ rule1 : (A B C)? && <<pred>>? rule2 ;\r
+ rule2 : (A|X) (B|Y) (C|Z);\r
+\r
+ This addition was suggested by Rienier van den Born (reinier@vnet.ibm.com)\r
+\r
+#109. (Changed in 1.33MR10) improved trace information\r
+\r
+ The quality of the trace information provided by the "-gd"\r
+ switch has been improved significantly. Here is an example\r
+ of the output from a test program. It shows the rule name,\r
+ the first token of lookahead, the call depth, and the guess\r
+ status:\r
+\r
+ exit rule gusxx {"?"} depth 2\r
+ enter rule gusxx {"?"} depth 2\r
+ enter rule gus1 {"o"} depth 3 guessing\r
+ guess done - returning to rule gus1 {"o"} at depth 3\r
+ (guess mode continues - an enclosing guess is still active)\r
+ guess done - returning to rule gus1 {"Z"} at depth 3\r
+ (guess mode continues - an enclosing guess is still active)\r
+ exit rule gus1 {"Z"} depth 3 guessing\r
+ guess done - returning to rule gusxx {"o"} at depth 2 (guess mode ends)\r
+ enter rule gus1 {"o"} depth 3\r
+ guess done - returning to rule gus1 {"o"} at depth 3 (guess mode ends)\r
+ guess done - returning to rule gus1 {"Z"} at depth 3 (guess mode ends)\r
+ exit rule gus1 {"Z"} depth 3\r
+ line 1: syntax error at "Z" missing SC\r
+ ...\r
+\r
+ Rule trace reporting is controlled by the value of the integer\r
+ [zz]traceOptionValue: when it is positive tracing is enabled,\r
+ otherwise it is disabled. Tracing during guess mode is controlled\r
+ by the value of the integer [zz]traceGuessOptionValue. When\r
+ it is positive AND [zz]traceOptionValue is positive rule trace\r
+ is reported in guess mode.\r
+\r
+ The values of [zz]traceOptionValue and [zz]traceGuessOptionValue\r
+ can be adjusted by subroutine calls listed below.\r
+\r
+ Depending on the presence or absence of the antlr -gd switch\r
+ the variable [zz]traceOptionValueDefault is set to 0 or 1. When\r
+ the parser is initialized or [zz]traceReset() is called the\r
+ value of [zz]traceOptionValueDefault is copied to [zz]traceOptionValue.\r
+ The value of [zz]traceGuessOptionValue is always initialzed to 1,\r
+ but, as noted earlier, nothing will be reported unless\r
+ [zz]traceOptionValue is also positive.\r
+\r
+ When the parser state is saved/restored the value of the trace\r
+ variables are also saved/restored. If a restore causes a change in\r
+ reporting behavior from on to off or vice versa this will be reported.\r
+\r
+ When the -gd option is selected, the macro "#define zzTRACE_RULES"\r
+ is added to appropriate output files.\r
+\r
+ C++ mode\r
+ --------\r
+ int traceOption(int delta)\r
+ int traceGuessOption(int delta)\r
+ void traceReset()\r
+ int traceOptionValueDefault\r
+\r
+ C mode\r
+ --------\r
+ int zzTraceOption(int delta)\r
+ int zzTraceGuessOption(int delta)\r
+ void zzTraceReset()\r
+ int zzTraceOptionValueDefault\r
+\r
+ The argument "delta" is added to the traceOptionValue. To\r
+ turn on trace when inside a particular rule one:\r
+\r
+ rule : <<traceOption(+1);>>\r
+ (\r
+ rest-of-rule\r
+ )\r
+ <<traceOption(-1);>>\r
+ ; /* fail clause */ <<traceOption(-1);>>\r
+\r
+ One can use the same idea to turn *off* tracing within a\r
+ rule by using a delta of (-1).\r
+\r
+ An improvement in the rule trace was suggested by Sramji\r
+ Ramanathan (ps@kumaran.com).\r
+\r
+#108. A Note on Deallocation of Variables Allocated in Guess Mode\r
+\r
+ NOTE\r
+ ------------------------------------------------------\r
+ This mechanism only works for heap allocated variables\r
+ ------------------------------------------------------\r
+\r
+ The rewrite of the trace provides the machinery necessary\r
+ to properly free variables or undo actions following a\r
+ failed guess.\r
+\r
+ The macro zzUSER_GUESS_HOOK(guessSeq,zzrv) is expanded\r
+ as part of the zzGUESS macro. When a guess is opened\r
+ the value of zzrv is 0. When a longjmp() is executed to\r
+ undo the guess, the value of zzrv will be 1.\r
+\r
+ The macro zzUSER_GUESS_DONE_HOOK(guessSeq) is expanded\r
+ as part of the zzGUESS_DONE macro. This is executed\r
+ whether the guess succeeds or fails as part of closing\r
+ the guess.\r
+\r
+ The guessSeq is a sequence number which is assigned to each\r
+ guess and is incremented by 1 for each guess which becomes\r
+ active. It is needed by the user to associate the start of\r
+ a guess with the failure and/or completion (closing) of a\r
+ guess.\r
+\r
+ Guesses are nested. They must be closed in the reverse\r
+ of the order that they are opened.\r
+\r
+ In order to free memory used by a variable during a guess\r
+ a user must write a routine which can be called to\r
+ register the variable along with the current guess sequence\r
+ number provided by the zzUSER_GUESS_HOOK macro. If the guess\r
+ fails, all variables tagged with the corresponding guess\r
+ sequence number should be released. This is ugly, but\r
+ it would require a major rewrite of antlr 1.33 to use\r
+ some mechanism other than setjmp()/longjmp().\r
+\r
+ The order of calls for a *successful* guess would be:\r
+\r
+ zzUSER_GUESS_HOOK(guessSeq,0);\r
+ zzUSER_GUESS_DONE_HOOK(guessSeq);\r
+\r
+ The order of calls for a *failed* guess would be:\r
+\r
+ zzUSER_GUESS_HOOK(guessSeq,0);\r
+ zzUSER_GUESS_HOOK(guessSeq,1);\r
+ zzUSER_GUESS_DONE_HOOK(guessSeq);\r
+\r
+ The default definitions of these macros are empty strings.\r
+\r
+ Here is an example in C++ mode. The zzUSER_GUESS_HOOK and\r
+ zzUSER_GUESS_DONE_HOOK macros and myGuessHook() routine\r
+ can be used without change in both C and C++ versions.\r
+\r
+ ----------------------------------------------------------------------\r
+ <<\r
+\r
+ #include "AToken.h"\r
+\r
+ typedef ANTLRCommonToken ANTLRToken;\r
+\r
+ #include "DLGLexer.h"\r
+\r
+ int main() {\r
+\r
+ {\r
+ DLGFileInput in(stdin);\r
+ DLGLexer lexer(&in,2000);\r
+ ANTLRTokenBuffer pipe(&lexer,1);\r
+ ANTLRCommonToken aToken;\r
+ P parser(&pipe);\r
+\r
+ lexer.setToken(&aToken);\r
+ parser.init();\r
+ parser.start();\r
+ };\r
+\r
+ fclose(stdin);\r
+ fclose(stdout);\r
+ return 0;\r
+ }\r
+\r
+ >>\r
+\r
+ <<\r
+ char *s=NULL;\r
+\r
+ #undef zzUSER_GUESS_HOOK\r
+ #define zzUSER_GUESS_HOOK(guessSeq,zzrv) myGuessHook(guessSeq,zzrv);\r
+ #undef zzUSER_GUESS_DONE_HOOK\r
+ #define zzUSER_GUESS_DONE_HOOK(guessSeq) myGuessHook(guessSeq,2);\r
+\r
+ void myGuessHook(int guessSeq,int zzrv) {\r
+ if (zzrv == 0) {\r
+ fprintf(stderr,"User hook: starting guess #%d\n",guessSeq);\r
+ } else if (zzrv == 1) {\r
+ free (s);\r
+ s=NULL;\r
+ fprintf(stderr,"User hook: failed guess #%d\n",guessSeq);\r
+ } else if (zzrv == 2) {\r
+ free (s);\r
+ s=NULL;\r
+ fprintf(stderr,"User hook: ending guess #%d\n",guessSeq);\r
+ };\r
+ }\r
+\r
+ >>\r
+\r
+ #token A "a"\r
+ #token "[\t \ \n]" <<skip();>>\r
+\r
+ class P {\r
+\r
+ start : (top)+\r
+ ;\r
+\r
+ top : (which) ? <<fprintf(stderr,"%s is a which\n",s); free(s); s=NULL; >>\r
+ | other <<fprintf(stderr,"%s is an other\n",s); free(s); s=NULL; >>\r
+ ; <<if (s != NULL) free(s); s=NULL; >>\r
+\r
+ which : which2\r
+ ;\r
+\r
+ which2 : which3\r
+ ;\r
+ which3\r
+ : (label)? <<fprintf(stderr,"%s is a label\n",s);>>\r
+ | (global)? <<fprintf(stderr,"%s is a global\n",s);>>\r
+ | (exclamation)? <<fprintf(stderr,"%s is an exclamation\n",s);>>\r
+ ;\r
+\r
+ label : <<s=strdup(LT(1)->getText());>> A ":" ;\r
+\r
+ global : <<s=strdup(LT(1)->getText());>> A "::" ;\r
+\r
+ exclamation : <<s=strdup(LT(1)->getText());>> A "!" ;\r
+\r
+ other : <<s=strdup(LT(1)->getText());>> "other" ;\r
+\r
+ }\r
+ ----------------------------------------------------------------------\r
+\r
+ This is a silly example, but illustrates the idea. For the input\r
+ "a ::" with tracing enabled the output begins:\r
+\r
+ ----------------------------------------------------------------------\r
+ enter rule "start" depth 1\r
+ enter rule "top" depth 2\r
+ User hook: starting guess #1\r
+ enter rule "which" depth 3 guessing\r
+ enter rule "which2" depth 4 guessing\r
+ enter rule "which3" depth 5 guessing\r
+ User hook: starting guess #2\r
+ enter rule "label" depth 6 guessing\r
+ guess failed\r
+ User hook: failed guess #2\r
+ guess done - returning to rule "which3" at depth 5 (guess mode continues\r
+ - an enclosing guess is still active)\r
+ User hook: ending guess #2\r
+ User hook: starting guess #3\r
+ enter rule "global" depth 6 guessing\r
+ exit rule "global" depth 6 guessing\r
+ guess done - returning to rule "which3" at depth 5 (guess mode continues\r
+ - an enclosing guess is still active)\r
+ User hook: ending guess #3\r
+ enter rule "global" depth 6 guessing\r
+ exit rule "global" depth 6 guessing\r
+ exit rule "which3" depth 5 guessing\r
+ exit rule "which2" depth 4 guessing\r
+ exit rule "which" depth 3 guessing\r
+ guess done - returning to rule "top" at depth 2 (guess mode ends)\r
+ User hook: ending guess #1\r
+ enter rule "which" depth 3\r
+ .....\r
+ ----------------------------------------------------------------------\r
+\r
+ Remember:\r
+\r
+ (a) Only init-actions are executed during guess mode.\r
+ (b) A rule can be invoked multiple times during guess mode.\r
+ (c) If the guess succeeds the rule will be called once more\r
+ without guess mode so that normal actions will be executed.\r
+ This means that the init-action might need to distinguish\r
+ between guess mode and non-guess mode using the variable\r
+ [zz]guessing.\r
+\r
+#101. (Changed in 1.33MR10) antlr -info command line switch\r
+\r
+ -info\r
+\r
+ p - extra predicate information in generated file\r
+\r
+ t - information about tnode use:\r
+ at the end of each rule in generated file\r
+ summary on stderr at end of program\r
+\r
+ m - monitor progress\r
+ prints name of each rule as it is started\r
+ flushes output at start of each rule\r
+\r
+ f - first/follow set information to stdout\r
+\r
+ 0 - no operation (added in 1.33MR11)\r
+\r
+ The options may be combined and may appear in any order.\r
+ For example:\r
+\r
+ antlr -info ptm -CC -gt -mrhoist on mygrammar.g\r
+\r
+#100a. (Changed in 1.33MR10) Predicate tree simplification\r
+\r
+ When the same predicates can be referenced in more than one\r
+ alternative of a block large predicate trees can be formed.\r
+\r
+ The difference that these optimizations make is so dramatic\r
+ that I have decided to use it even when -mrhoist is not selected.\r
+\r
+ Consider the following grammar:\r
+\r
+ start : ( all )* ;\r
+\r
+ all : a\r
+ | d\r
+ | e\r
+ | f\r
+ ;\r
+\r
+ a : c A B\r
+ | c A C\r
+ ;\r
+\r
+ c : <<AAA(LATEXT(2))>>?\r
+ ;\r
+\r
+ d : <<BBB(LATEXT(2))>>? B C\r
+ ;\r
+\r
+ e : <<CCC(LATEXT(2))>>? B C\r
+ ;\r
+\r
+ f : e X Y\r
+ ;\r
+\r
+ In rule "a" there is a reference to rule "c" in both alternatives.\r
+ The length of the predicate AAA is k=2 and it can be followed in\r
+ alternative 1 only by (A B) while in alternative 2 it can be\r
+ followed only by (A C). Thus they do not have identical context.\r
+\r
+ In rule "all" the alternatives which refer to rules "e" and "f" allow\r
+ elimination of the duplicate reference to predicate CCC.\r
+\r
+ The table below summarized the kind of simplification performed by\r
+ 1.33MR10. In the table, X and Y stand for single predicates\r
+ (not trees).\r
+\r
+ (OR X (OR Y (OR Z))) => (OR X Y Z)\r
+ (AND X (AND Y (AND Z))) => (AND X Y Z)\r
+\r
+ (OR X (... (OR X Y) ... )) => (OR X (... Y ... ))\r
+ (AND X (... (AND X Y) ... )) => (AND X (... Y ... ))\r
+ (OR X (... (AND X Y) ... )) => (OR X (... ... ))\r
+ (AND X (... (OR X Y) ... )) => (AND X (... ... ))\r
+\r
+ (AND X) => X\r
+ (OR X) => X\r
+\r
+ In a test with a complex grammar for a real application, a predicate\r
+ tree with six OR nodes and 12 leaves was reduced to "(OR X Y Z)".\r
+\r
+ In 1.33MR10 there is a greater effort to release memory used\r
+ by predicates once they are no longer in use.\r
+\r
+#100b. (Changed in 1.33MR10) Suppression of extra predicate tests\r
+\r
+ The following optimizations require that -mrhoist be selected.\r
+\r
+ It is relatively easy to optimize the code generated for predicate\r
+ gates when they are of the form:\r
+\r
+ (AND X Y Z ...)\r
+ or (OR X Y Z ...)\r
+\r
+ where X, Y, Z, and "..." represent individual predicates (leaves) not\r
+ predicate trees.\r
+\r
+ If the predicate is an AND the contexts of the X, Y, Z, etc. are\r
+ ANDed together to create a single Tree context for the group and\r
+ context tests for the individual predicates are suppressed:\r
+\r
+ --------------------------------------------------\r
+ Note: This was incorrect. The contexts should be\r
+ ORed together. This has been fixed. A more \r
+ complete description is available in item #152.\r
+ ---------------------------------------------------\r
+\r
+ Optimization 1: (AND X Y Z ...)\r
+\r
+ Suppose the context for Xtest is LA(1)==LP and the context for\r
+ Ytest is LA(1)==LP && LA(2)==ID.\r
+\r
+ Without the optimization the code would resemble:\r
+\r
+ if (lookaheadContext &&\r
+ !(LA(1)==LP && LA(1)==LP && LA(2)==ID) ||\r
+ ( (! LA(1)==LP || Xtest) &&\r
+ (! (LA(1)==LP || LA(2)==ID) || Xtest)\r
+ )) {...\r
+\r
+ With the -mrhoist optimization the code would resemble:\r
+\r
+ if (lookaheadContext &&\r
+ ! (LA(1)==LP && LA(2)==ID) || (Xtest && Ytest) {...\r
+\r
+ Optimization 2: (OR X Y Z ...) with identical contexts\r
+\r
+ Suppose the context for Xtest is LA(1)==ID and for Ytest\r
+ the context is also LA(1)==ID.\r
+\r
+ Without the optimization the code would resemble:\r
+\r
+ if (lookaheadContext &&\r
+ ! (LA(1)==ID || LA(1)==ID) ||\r
+ (LA(1)==ID && Xtest) ||\r
+ (LA(1)==ID && Ytest) {...\r
+\r
+ With the -mrhoist optimization the code would resemble:\r
+\r
+ if (lookaheadContext &&\r
+ (! LA(1)==ID) || (Xtest || Ytest) {...\r
+\r
+ Optimization 3: (OR X Y Z ...) with distinct contexts\r
+\r
+ Suppose the context for Xtest is LA(1)==ID and for Ytest\r
+ the context is LA(1)==LP.\r
+\r
+ Without the optimization the code would resemble:\r
+\r
+ if (lookaheadContext &&\r
+ ! (LA(1)==ID || LA(1)==LP) ||\r
+ (LA(1)==ID && Xtest) ||\r
+ (LA(1)==LP && Ytest) {...\r
+\r
+ With the -mrhoist optimization the code would resemble:\r
+\r
+ if (lookaheadContext &&\r
+ (zzpf=0,\r
+ (LA(1)==ID && (zzpf=1) && Xtest) ||\r
+ (LA(1)==LP && (zzpf=1) && Ytest) ||\r
+ !zzpf) {\r
+\r
+ These may appear to be of similar complexity at first,\r
+ but the non-optimized version contains two tests of each\r
+ context while the optimized version contains only one\r
+ such test, as well as eliminating some of the inverted\r
+ logic (" !(...) || ").\r
+\r
+ Optimization 4: Computation of predicate gate trees\r
+\r
+ When generating code for the gates of predicate expressions\r
+ antlr 1.33 vanilla uses a recursive procedure to generate\r
+ "&&" and "||" expressions for testing the lookahead. As each\r
+ layer of the predicate tree is exposed a new set of "&&" and\r
+ "||" expressions on the lookahead are generated. In many\r
+ cases the lookahead being tested has already been tested.\r
+\r
+ With -mrhoist a lookahead tree is computed for the entire\r
+ lookahead expression. This means that predicates with identical\r
+ context or context which is a subset of another predicate's\r
+ context disappear.\r
+\r
+ This is especially important for predicates formed by rules\r
+ like the following:\r
+\r
+ uppperCaseVowel : <<isUpperCase(LATEXT(1))>>? vowel;\r
+ vowel: : <<isVowel(LATEXT(1))>>? LETTERS;\r
+\r
+ These predicates are combined using AND since both must be\r
+ satisfied for rule upperCaseVowel. They have identical\r
+ context which makes this optimization very effective.\r
+\r
+ The affect of Items #100a and #100b together can be dramatic. In\r
+ a very large (but real world) grammar one particular predicate\r
+ expression was reduced from an (unreadable) 50 predicate leaves,\r
+ 195 LA(1) terms, and 5500 characters to an (easily comprehensible)\r
+ 3 predicate leaves (all different) and a *single* LA(1) term.\r
+\r
+#98. (Changed in 1.33MR10) Option "-info p"\r
+\r
+ When the user selects option "-info p" the program will generate\r
+ detailed information about predicates. If the user selects\r
+ "-mrhoist on" additional detail will be provided explaining\r
+ the promotion and suppression of predicates. The output is part\r
+ of the generated file and sandwiched between #if 0/#endif statements.\r
+\r
+ Consider the following k=1 grammar:\r
+\r
+ start : ( all ) * ;\r
+\r
+ all : ( a\r
+ | b\r
+ )\r
+ ;\r
+\r
+ a : c B\r
+ ;\r
+\r
+ c : <<LATEXT(1)>>?\r
+ | B\r
+ ;\r
+\r
+ b : <<LATEXT(1)>>? X\r
+ ;\r
+\r
+ Below is an excerpt of the output for rule "start" for the three\r
+ predicate options (off, on, and maintenance release style hoisting).\r
+\r
+ For those who do not wish to use the "-mrhoist on" option for code\r
+ generation the option can be used in a "diagnostic" mode to provide\r
+ valuable information:\r
+\r
+ a. where one should insert null actions to inhibit hoisting\r
+ b. a chain of rule references which shows where predicates are\r
+ being hoisted\r
+\r
+ ======================================================================\r
+ Example of "-info p" with "-mrhoist on"\r
+ ======================================================================\r
+ #if 0\r
+\r
+ Hoisting of predicate suppressed by alternative without predicate.\r
+ The alt without the predicate includes all cases where the\r
+ predicate is false.\r
+\r
+ WITH predicate: line 11 v36.g\r
+ WITHOUT predicate: line 12 v36.g\r
+\r
+ The context set for the predicate:\r
+\r
+ B\r
+\r
+ The lookahead set for alt WITHOUT the semantic predicate:\r
+\r
+ B\r
+\r
+ The predicate:\r
+\r
+ pred << LATEXT(1)>>? depth=k=1 rule c line 11 v36.g\r
+\r
+ set context:\r
+ B\r
+ tree context: null\r
+\r
+ Chain of referenced rules:\r
+\r
+ #0 in rule start (line 1 v36.g) to rule all\r
+ #1 in rule all (line 3 v36.g) to rule a\r
+ #2 in rule a (line 8 v36.g) to rule c\r
+ #3 in rule c (line 11 v36.g)\r
+\r
+ #endif\r
+ &&\r
+ #if 0\r
+\r
+ pred << LATEXT(1)>>? depth=k=1 rule b line 15 v36.g\r
+\r
+ set context:\r
+ X\r
+ tree context: null\r
+\r
+ #endif\r
+ ======================================================================\r
+ Example of "-info p" with the default -prc setting ( "-prc off")\r
+ ======================================================================\r
+ #if 0\r
+\r
+ OR\r
+ pred << LATEXT(1)>>? depth=k=1 rule c line 11 v36.g\r
+\r
+ set context:\r
+ nil\r
+ tree context: null\r
+\r
+ pred << LATEXT(1)>>? depth=k=1 rule b line 15 v36.g\r
+\r
+ set context:\r
+ nil\r
+ tree context: null\r
+\r
+ #endif\r
+ ======================================================================\r
+ Example of "-info p" with "-prc on" and "-mrhoist off"\r
+ ======================================================================\r
+ #if 0\r
+\r
+ OR\r
+ pred << LATEXT(1)>>? depth=k=1 rule c line 11 v36.g\r
+\r
+ set context:\r
+ B\r
+ tree context: null\r
+\r
+ pred << LATEXT(1)>>? depth=k=1 rule b line 15 v36.g\r
+\r
+ set context:\r
+ X\r
+ tree context: null\r
+\r
+ #endif\r
+ ======================================================================\r
+\r
+#60. (Changed in 1.33MR7) Major changes to exception handling\r
+\r
+ There were significant problems in the handling of exceptions\r
+ in 1.33 vanilla. The general problem is that it can only\r
+ process one level of exception handler. For example, a named\r
+ exception handler, an exception handler for an alternative, or\r
+ an exception for a subrule always went to the rule's exception\r
+ handler if there was no "catch" which matched the exception.\r
+\r
+ In 1.33MR7 the exception handlers properly "nest". If an\r
+ exception handler does not have a matching "catch" then the\r
+ nextmost outer exception handler is checked for an appropriate\r
+ "catch" clause, and so on until an exception handler with an\r
+ appropriate "catch" is found.\r
+\r
+ There are still undesirable features in the way exception\r
+ handlers are implemented, but I do not have time to fix them\r
+ at the moment:\r
+\r
+ The exception handlers for alternatives are outside the\r
+ block containing the alternative. This makes it impossible\r
+ to access variables declared in a block or to resume the\r
+ parse by "falling through". The parse can still be easily\r
+ resumed in other ways, but not in the most natural fashion.\r
+\r
+ This results in an inconsistentcy between named exception\r
+ handlers and exception handlers for alternatives. When\r
+ an exception handler for an alternative "falls through"\r
+ it goes to the nextmost outer handler - not the "normal\r
+ action".\r
+\r
+ A major difference between 1.33MR7 and 1.33 vanilla is\r
+ the default action after an exception is caught:\r
+\r
+ 1.33 Vanilla\r
+ ------------\r
+ In 1.33 vanilla the signal value is set to zero ("NoSignal")\r
+ and the code drops through to the code following the exception.\r
+ For named exception handlers this is the "normal action".\r
+ For alternative exception handlers this is the rule's handler.\r
+\r
+ 1.33MR7\r
+ -------\r
+ In 1.33MR7 the signal value is NOT automatically set to zero.\r
+\r
+ There are two cases:\r
+\r
+ For named exception handlers: if the signal value has been\r
+ set to zero the code drops through to the "normal action".\r
+\r
+ For all other cases the code branches to the nextmost outer\r
+ exception handler until it reaches the handler for the rule.\r
+\r
+ The following macros have been defined for convenience:\r
+\r
+ C/C++ Mode Name\r
+ --------------------\r
+ (zz)suppressSignal\r
+ set signal & return signal arg to 0 ("NoSignal")\r
+ (zz)setSignal(intValue)\r
+ set signal & return signal arg to some value\r
+ (zz)exportSignal\r
+ copy the signal value to the return signal arg\r
+\r
+ I'm not sure why PCCTS make a distinction between the local\r
+ signal value and the return signal argument, but I'm loathe\r
+ to change the code. The burden of copying the local signal\r
+ value to the return signal argument can be given to the\r
+ default signal handler, I suppose.\r
+\r
+#53. (Explanation for 1.33MR6) What happens after an exception is caught ?\r
+\r
+ The Book is silent about what happens after an exception\r
+ is caught.\r
+\r
+ The following code fragment prints "Error Action" followed\r
+ by "Normal Action".\r
+\r
+ test : Word ex:Number <<printf("Normal Action\n");>>\r
+ exception[ex]\r
+ catch NoViableAlt:\r
+ <<printf("Error Action\n");>>\r
+ ;\r
+\r
+ The reason for "Normal Action" is that the normal flow of the\r
+ program after a user-written exception handler is to "drop through".\r
+ In the case of an exception handler for a rule this results in\r
+ the exection of a "return" statement. In the case of an\r
+ exception handler attached to an alternative, rule, or token\r
+ this is the code that would have executed had there been no\r
+ exception.\r
+\r
+ The user can achieve the desired result by using a "return"\r
+ statement.\r
+\r
+ test : Word ex:Number <<printf("Normal Action\n");>>\r
+ exception[ex]\r
+ catch NoViableAlt:\r
+ <<printf("Error Action\n"); return;>>\r
+ ;\r
+\r
+ The most powerful mechanism for recovery from parse errors\r
+ in pccts is syntactic predicates because they provide\r
+ backtracking. Exceptions allow "return", "break",\r
+ "consumeUntil(...)", "goto _handler", "goto _fail", and\r
+ changing the _signal value.\r
+\r
+#41. (Added in 1.33MR6) antlr -stdout\r
+\r
+ Using "antlr -stdout ..." forces the text that would\r
+ normally go to the grammar.c or grammar.cpp file to\r
+ stdout.\r
+\r
+#40. (Added in 1.33MR6) antlr -tab to change tab stops\r
+\r
+ Using "antlr -tab number ..." changes the tab stops\r
+ for the grammar.c or grammar.cpp file. The number\r
+ must be between 0 and 8. Using 0 gives tab characters,\r
+ values between 1 and 8 give the appropriate number of\r
+ space characters.\r
+\r
+#34. (Added to 1.33MR1) Add public DLGLexerBase::set_line(int newValue)\r
+\r
+ Previously there was no public function for changing the line\r
+ number maintained by the lexer.\r
+\r
+#28. (Added to 1.33MR1) More control over DLG header\r
+\r
+ Version 1.33MR1 adds the following directives to PCCTS\r
+ for C++ mode:\r
+\r
+ #lexprefix <<source code>>\r
+\r
+ Adds source code to the DLGLexer.h file\r
+ after the #include "DLexerBase.h" but\r
+ before the start of the class definition.\r
+\r
+ #lexmember <<source code>>\r
+\r
+ Adds source code to the DLGLexer.h file\r
+ as part of the DLGLexer class body. It\r
+ appears immediately after the start of\r
+ the class and a "public: statement.\r
+\r
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