[antlr-interest] How to use predicate or workaround the bug ?

[Ilia Kantor]

Thanks for answering, Ter. The book is going to be a must-read for me =).

Still confused, what's up with predicate:

curly_block
	:	
	 {true}? LCURL exprs? RCURL -> TEXT[$LCURL] exprs? TEXT[$RCURL] |
	   LCURL exprs? RCURL -> exprs? 

The predicate does not reference anything, it's a plain "true" value.

How should I change it to work ? 

The ultimate question is  how to make 'input.index()==0' to work, but 'true' 
fails to compile also..

>  From the book:
>
> Another limitation on semantic predicates is that they should not
> reference local variables, parameters, or anything else that is not
> visible to all rules just in case they are hoisted out of one rule
> into another's prediction DFA. If you are positive that the predicate
> will not be hoisted out of the rule, you can use a parameter, for
> example, to alter prediction in a rule:
>
> method[boolean allowConcrete]
>
>      :   {allowConcrete}?=> methodHead body
>      :
>      |   methodHead ';'
>
>      ;
>
> Workaround is a field or dynamically scope var.
>
> Ter
>
> On Jan 2, 2007, at 6:34 AM, Ilia Kantor wrote:
> > I'm using antlr 3b6 build from Tue Jan  2 14:28:20 UTC 2007. Also
> > tried 3b5.
> >
> > Trying to make use of predicate, but fail.. Is there a workaround ?
> >
> > Here I try to rewrite
> > 'LCURL  exprs? RCURL' into 'TEXT exprs? TEXT' in common case and strip
> > LCURL/RCURL if this LCURL/RCURL block is outmost, that is: if LCURL
> > is first
> > token.
> >
> > ==================== rule with predicate=====
> > curly_block
> >
> > 	 {input.index()==0}? LCURL exprs? RCURL -> exprs? |
> >      LCURL exprs? RCURL -> TEXT[$LCURL] exprs? TEXT[$RCURL]
> > ===================== error  ===========
> >
> >
> > ANTLR Parser Generator  Version 3.0b6 (??)  1989-2007
> > Exception in thread "main" java.lang.StackOverflowError
> >         at java.util.HashMap$KeyIterator.<init>(HashMap.java:875)
> >         at java.util.HashMap$KeyIterator.<init>(HashMap.java:875)
> >         at java.util.HashMap.newKeyIterator(HashMap.java:889)
> >         at java.util.HashMap$KeySet.iterator(HashMap.java:921)
> >         at java.util.HashSet.iterator(HashSet.java:154)
> >         at
> > org.antlr.analysis.DFAState.getGatedPredicatesInNFAConfigurations
> > (DFAState.java:695)
> >         at
> > org.antlr.codegen.CodeGenerator.canGenerateSwitch
> > (CodeGenerator.java:1119)
> >         at
> > org.antlr.codegen.ACyclicDFACodeGenerator.walkFixedDFAGeneratingStateM
> > achine(ACyclicDFACodeGenerator.java:72)
> >         at
> > org.antlr.codegen.ACyclicDFACodeGenerator.walkFixedDFAGeneratingStateM
> > achine(ACyclicDFACodeGenerator.java:146)
> > =..................... the latest line repeats many times ..........=
> >
> >
> >
> > ======= Full grammar ===========
> >
> >
> > /* putting this to tokens { .. } causes antlrworks bugs like "...no
> > lexer rule
> > for IF..." */
> > IF	:	{false}? .;
> > THEN	:	{false}? .;
> > ELSE	:	{false}? .;
> > EVAL	:	{false}? .;
> > TEXT	:	{false}? .;
> > RULE_PROPERTY	:	{false}? .;
> > RULE_PART	:	{false}? .;
> >
> > LCURL	:	'{';
> > RCURL	:	'}';
> >
> > RULE_CALL
> >
> > 	:	'#';
> >
> > CONTROL
> >
> > 	:	'~';
> >
> > SEMI:	';';
> >
> > DOT	:	'.';
> >
> > MINUS
> >
> > 	:	'-';
> >
> > GT	:	'>';
> >
> > SPECIAL_CHAR
> >
> > 	:	'`' | '!' | '@' | '$' | '%' | '^' | '&' | '*' | '(' | ')' |
> >
> > 	'+' | '=' | '[' | ']' | ':' | '\'' | '"' | '\\' | '|' | ',' | '<' |
> > 	 '/' | '?';
> >
> >
> >
> > fragment WS_CHAR  :
> >        (' '|'\r'|'\t'|'\u000C'|'\n' )
> >     ;
> >
> > WS	:	WS_CHAR+;
> >
> > // not SPECIAL_CHAR not WS_CHAR
> > WORD:
> > {
> > 	// check if previous token was CONTROL
> > 	Boolean afterControl = input.index()>0 && input.LT(-1)=='~';
> > }
> > 	(~ ('`' | '!' | '@' | '$' | '%' | '^' | '&' | '*' | '(' | ')' |
> > 	'+' | '=' | '[' | ']' | ':' | '\'' | '"' | '\\' | '|' | ',' | '<'
> >
> > | '/' | '?'
> > |
> > 	| '{'
> > 	| '~'
> > 	| '}'
> > 	| '#'
> > 	| ';'
> > 	| '.'
> > 	| '-'
> > 	| '>'
> > 	| ' '|'\r'|'\t'|'\u000C'|'\n' ) )+
> >
> > {
> >     if (afterControl) {
> >     	// output WORDs as commands if after control
> > 		if (getText().equalsIgnoreCase("if")) $type=IF;
> > 		else if (getText().equalsIgnoreCase("else")) $type=ELSE;
> > 		else if (getText().equalsIgnoreCase("then")) $type=THEN;
> > 	}
> > }
> > ;
> >
> >
> >
> > document
> >
> > 	:	 exprs;
> >
> > exprs:
> >         (expr)+
> > ;
> >
> >
> > expr:
> > (
> >         expr_no_semi -> expr_no_semi |
> >         SEMI -> TEXT[$SEMI]
> > )
> > ;
> >
> > exprs_no_semi
> >
> >         :       (expr_no_semi)+
> >
> > ;
> >
> >
> > expr_no_semi
> >
> >                 (expr_simple) | (curly_block)
> >         ;
> >
> >
> >
> > exprs_simple
> >
> >         :       (expr_simple)+
> >
> >         ;
> >
> > /* expression without curl at start and ; */
> > expr_simple
> >
> >         command
> >
> >         | rule_call
> >         | text
> >
> > ;
> >
> >
> > command:
> >          command_eval |
> >          command_if
> > ;
> >
> >
> > command_if
> >
> >         CONTROL IF LCURL exprs? command_if_part_then
> > command_if_part_else?
> > RCURL ->
> >         ^(IF exprs? command_if_part_then command_if_part_else?)
> > ;
> >
> >
> > command_if_part_else:
> >         CONTROL ELSE exprs? -> ^(ELSE exprs?)
> > ;
> >
> > command_if_part_then
> >
> >         : CONTROL THEN exprs? -> ^(THEN exprs?)
> >
> > ;
> >
> >
> >
> > command_eval:
> >         CONTROL LCURL exprs? RCURL -> ^(EVAL exprs?)
> > ;
> >
> >
> >
> > rule_call: RULE_CALL WORD -> ^(RULE_CALL WORD) |
> > 	RULE_CALL LCURL WORD rule_long_def_part* RCURL -> ^(RULE_CALL WORD
> > rule_long_def_part*)
> > ;
> >
> > rule_long_def_part
> >
> > 	:	MINUS GT WORD -> ^(RULE_PROPERTY WORD) |
> >
> > 		DOT WORD -> ^(RULE_PART WORD)
> > 	;
> >
> >
> > curly_block
> >
> > 	 {true}? LCURL exprs? RCURL -> exprs?
> >
> > 	 |  LCURL exprs? RCURL -> TEXT[$LCURL] exprs? TEXT[$RCURL]
> >
> > ;
> >
> > text:
> > 	DOT -> TEXT[$DOT] | MINUS -> TEXT[$MINUS] | WORD -> TEXT[$WORD]
> >
> > 	| WS -> TEXT[$WS] | GT -> TEXT[$GT] | SPECIAL_CHAR -> TEXT
> >
> > [$SPECIAL_CHAR]
> > ;