ANTLR4 Grammar only matching first part of parser rule

Question

I'm using ANTLR 4 to try and parse task definitions. The task definitions look a little like the following:

task = { priority = 10; };

My grammar file then looks like the following:

grammar TaskGrammar;

/* Parser rules */

task : 'task' ASSIGNMENT_OP block EOF;

logical_entity : (TRUE | FALSE) # LogicalConst
               | IDENTIFIER     # LogicalVariable
               ;

numeric_entity : DECIMAL              # NumericConst
               | IDENTIFIER           # NumericVariable
               ;

block : LBRACE (statement)* RBRACE SEMICOLON;

assignment : IDENTIFIER ASSIGNMENT_OP DECIMAL SEMICOLON
            | IDENTIFIER ASSIGNMENT_OP block SEMICOLON
            | IDENTIFIER ASSIGNMENT_OP QUOTED_STRING SEMICOLON
            | IDENTIFIER ASSIGNMENT_OP CONSTANT SEMICOLON;

functionCall : IDENTIFIER LPAREN (parameter)*? RPAREN SEMICOLON;

parameter : DECIMAL
            | QUOTED_STRING;

statement : assignment
            | functionCall;

/* Lexxer rules */

IF   : 'if' ;
THEN : 'then';

AND : 'and' ;
OR  : 'or' ;

TRUE  : 'true' ;
FALSE : 'false' ;

MULT  : '*' ;
DIV   : '/' ;
PLUS  : '+' ;
MINUS : '-' ;

GT : '>' ;
GE : '>=' ;
LT : '<' ;
LE : '<=' ;
EQ : '==' ;

ASSIGNMENT_OP : '=' ;

LPAREN : '(' ;
RPAREN : ')' ;

LBRACE : '{' ;
RBRACE : '}' ;

SEMICOLON : ';' ;

// DECIMAL, IDENTIFIER, COMMENTS, WS are set using regular expressions

DECIMAL : '-'?[0-9]+('.'[0-9]+)? ;

IDENTIFIER : [a-zA-Z_][a-zA-Z_0-9]* ;

Value: STR_EXT | QUOTED_STRING | SINGLE_QUOTED
;

STR_EXT
  :
  [a-zA-Z0-9_/\.,\-:=~+!?$&^*\[\]@|]+;

Comment
    :
    '#' ~[\r\n]*;

CONSTANT : StringCharacters;

QUOTED_STRING
  :
  '"' StringCharacters? '"'
  ;

fragment
StringCharacters
    :   (~["\\] | EscapeSequence)+
    ;
fragment
EscapeSequence
    :   '\\' [btnfr"'\\]?
    ;
SINGLE_QUOTED
:
'\'' ~['\\]* '\'';

// COMMENT and WS are stripped from the output token stream by sending
// to a different channel 'skip'

COMMENT : '//' .+? ('\n'|EOF) -> skip ;

WS : [ \r\t\u000C\n]+ -> skip ;

This grammar compiles fine in ANTLR, but when it comes to trying to use the parser, I get the following error:

line 1:0 mismatched input 'task = { priority = 10; return = AND; };' expecting 'task'
org.antlr.v4.runtime.InputMismatchException

It looks like the parser isn't recognising the block part of the definition, but I can't quite see why. The block parse rule definition should match as far as I can tell. I would expect to have a TaskContext, with a child BlockContext containing a single AssignmentContext. I get the TaskContext, but it has the above exception.

Am I missing something here? This is my first attempt at using Antler, so may be getting confused between Lexxer and Parser rules...

Answer 1

Your STR_EXT consumes the entire input. That rule has to go: ANTLR's lexer will always try to match as much characters as possible.

I also see that CONSTANT might consume that entire input. It has to go to, or at least be changed to consume less chars.