antlr gated predicate - antlr

Question

This is a follow-up question from Antlr superfluous Predicate required? where I stated my problem in a simplified way, however it could not be solved there.
I have the following grammar and when I delete the {true}?=> predicates, the text is not recognized anymore. The input string is MODULE main LTLSPEC H {} {} {o} FALSE;. Note that the trailing ; is not tokenized as EOC, but as IGNORE. When I add {true}?=> to the EOC rule ; is tokenized as EOC.
I tried this from command-line with antlr-v3.3 and v3.4 without difference. Thanks in advance, I appreciate your help.
grammar NusmvInput;
options {
language = Java;
}
#parser::members{
public static void main(String[] args) throws Exception {
NusmvInputLexer lexer = new NusmvInputLexer(new ANTLRStringStream("MODULE main LTLSPEC H {} {} {o} FALSE;"));
NusmvInputParser parser = new NusmvInputParser(new CommonTokenStream(lexer));
parser.specification();
}
}
#lexer::members{
private boolean inLTL = false;
}
specification :
module+ EOF
;
module :
MODULE module_decl
;
module_decl :
NAME parameter_list ;
parameter_list
: ( LP (parameter ( COMMA parameter )*)? RP )?
;
parameter
: (NAME | INTEGER )
;
/**************
*** LEXER
**************/
COMMA
:{!inLTL}?=> ','
;
OTHER
: {!inLTL}?=>( '&' | '|' | 'xor' | 'xnor' | '=' | '!' |
'<' | '>' | '-' | '+' | '*' | '/' |
'mod' | '[' | ']' | '?')
;
RCP
: {!inLTL}?=>'}'
;
LCP
: {!inLTL}?=>'{'
;
LP
: {!inLTL}?=>'('
;
RP
: {!inLTL}?=>')'
;
MODULE
: {true}?=> 'MODULE' {inLTL = false;}
;
LTLSPEC
: {true}?=> 'LTLSPEC'
{inLTL = true; skip(); }
;
EOC
: ';'
{
if (inLTL){
inLTL = false;
skip();
}
}
;
WS
: (' ' | '\t' | '\n' | '\r')+ {$channel = HIDDEN;}
;
COMMENT
: '--' .* ('\n' | '\r') {$channel = HIDDEN;}
;
INTEGER
: {!inLTL}?=> ('0'..'9')+
;
NAME
:{!inLTL}?=> ('A'..'Z' | 'a'..'z') ('a'..'z' | 'A'..'Z' | '0'..'9' | '_' | '$' | '#' | '-')*
;
IGNORE
: {inLTL}?=> . {skip();}
;

Answer 1

It seems that without a predicate before MODULE and LTLSPEC, the NAME gets precedence over them even if these tokens are defined before the NAME token. Whether this is by design or a bug, I don't know.
However, the way you're trying to solve it seems rather complicated. As far as I can see, you seem to want to ignore (or skip) input starting with LTLSPEC and ending with a semi colon. Why not do something like this instead:
specification : module+ EOF;
module : MODULE module_decl;
module_decl : NAME parameter_list;
parameter_list : (LP (parameter ( COMMA parameter )*)? RP)?;
parameter : (NAME | INTEGER);
MODULE : 'MODULE';
LTLSPEC : 'LTLSPEC' ~';'* ';' {skip();};
COMMA : ',';
OTHER : ( '&' | '|' | 'xor' | 'xnor' | '=' | '!' |
'<' | '>' | '-' | '+' | '*' | '/' |
'mod' | '[' | ']' | '?')
;
RCP : '}';
LCP : '{';
LP : '(';
RP : ')';
EOC : ';';
WS : (' ' | '\t' | '\n' | '\r')+ {$channel = HIDDEN;};
COMMENT : '--' .* ('\n' | '\r') {$channel = HIDDEN;};
INTEGER : ('0'..'9')+;
NAME : ('A'..'Z' | 'a'..'z') ('a'..'z' | 'A'..'Z' | '0'..'9' | '_' | '$' | '#' | '-')*;