I just started work on a grammar to read well, context free grammars,
and am running into a problem. (I'm probably just doing something dumb.)
I've attached my grammar.
The ARROW token (used between the left and right sides of a production)
should recognize either ':' or '->', but the AntlrWorks interpreter only
accepts '->'. If I try to parse the input 'a -> b;', I get the proper
result. If I try to parse 'a : b;', it gives a MismatchedTokenException.
(I am pretty sure I saw the same behavior using the debug option, but I
don't have the JDK on this computer and can't confirm it.)
The rules in question are:
COLON : ':'; // used in multiple places
ARROW
: '->'
| COLON
;
production
: SYMBOL ARROW disjunction SEMICOLON
;
(If you're curious, COLON is used elsewhere so I put it into its own
token. (I saw a couple posts from this mailing list previously
recommending not using string literals in parsing rules.) What I'm
posting is a slightly simplified version where that other use is
removed. It doesn't change the behavior though.)
The parse tree AntlrWork's interpreter shows for 'a->b;' is
rules
|
production
|
+-----+---+-----+----------+
| | | |
a -> disjunction ;
|
termString
|
term
|
atom
|
b
But for 'a: b;' I get
rules
|
production
|
+---------+-----+
| |
a MismatchedTokenException(11!=16)
Can anyone explain what's going on?
Thanks,
Evan
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grammar cfg;
PIPE : '|';
PLUS : '+';
STAR : '*';
LPAREN : '(';
RPAREN : ')';
LBRACE : '{';
RBRACE : '}';
COLON : ':';
SEMICOLON : ';';
NUMBER
: '0'..'9'+
;
fragment LETTER
: 'a'..'z' | 'A'..'Z' | '0'..'9' | '_' | '-'
;
// Encompasses both terminals and nonterminals. Distinguishing them is done
later.
// This is way more broad than your typical programming language identifier:
leading
// digits are OK and hyphens are OK.
SYMBOL
: LETTER+
;
// For separating productions and rules
ARROW
: '->'
| COLON
;
WHITESPACE
: '\r' | '\n' | ' ' { $channel = HIDDEN; }
;
// Either a symbol or id:symbol, or a parenthisized expression.
atom
: SYMBOL
| NUMBER COLON SYMBOL
| LPAREN disjunction RPAREN
;
term
: atom (STAR|PLUS)?
;
// Represents concatenation
termString
: term+
;
disjunction
: termString (PIPE termString)*
;
production
: SYMBOL ARROW disjunction SEMICOLON
;
rules
: production+
;
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