ANTLR grammar from bison - antlr

Question

I'm trying to translate a grammar from bison to ANTLR. The grammar itself is pretty simple in bison but I cannot find a simple way for doing this.
Grammar in bison:
expr = expr or expr | expr and expr | (expr)
Any hints/links/pointers are welcome.
Thanks,
Iulian

Answer 1

In ANTLR3, you cannot create left recursive rules (ANTLR4 can handle left recursion in certain cases):
a : a b
;
tail recursion is fine:
a : b a
;
For more information on left recursive rules, see ANTLR's Wiki.
So, your example could look like:
parse
: expr+ EOF
;
expr
: orExpr
;
orExpr
: andExpr ('or' andExpr)*
;
andExpr
: atom ('and' atom)*
;
atom
: Boolean
| '(' expr ')'
;
Boolean
: 'true'
| 'false'
;
Here's a small demo in Java:
grammar BoolExp;
#members {
public static void main(String[] args) throws Exception {
if(args.length != 1) {
System.out.println("Usage:");
System.out.println(" - Windows : java -cp .;antlr-3.2.jar BoolExpParser \"EXPRESSION\"");
System.out.println(" - *nix/MacOS : java -cp .:antlr-3.2.jar BoolExpParser \"EXPRESSION\"");
System.exit(0);
}
ANTLRStringStream in = new ANTLRStringStream(args[0]);
BoolExpLexer lexer = new BoolExpLexer(in);
CommonTokenStream tokens = new CommonTokenStream(lexer);
BoolExpParser parser = new BoolExpParser(tokens);
parser.parse();
}
}
parse
: e=expr EOF {System.out.println($e.bool);}
;
expr returns [boolean bool]
: e=orExpr {$bool = $e.bool;}
;
orExpr returns [boolean bool]
: e1=andExpr {$bool = $e1.bool;}
('or' e2=andExpr {$bool = $bool || $e2.bool;}
)*
;
andExpr returns [boolean bool]
: e1=atom {$bool = $e1.bool;}
('and' e2=atom {$bool = $bool && $e2.bool;}
)*
;
atom returns [boolean bool]
: b=Boolean {$bool = new Boolean($b.text).booleanValue();}
| '(' e=expr ')' {$bool = $e.bool;}
;
Boolean
: 'true'
| 'false'
;
Space
: (' ' | '\t' | '\n' | '\r') {skip();}
;
First create a lexer & parser (1) and then compile all source files (2). Finally, execute the BoolExpParser class (3).
1
// Windows & *nix/MacOS
java -cp antlr-3.2.jar org.antlr.Tool BoolExp.g
2
// Windows
javac -cp .;antlr-3.2.jar *.java
// *nix/MacOS
javac -cp .:antlr-3.2.jar *.java
3
// Windows
java -cp .;antlr-3.2.jar BoolExpParser "false and true or true"
// *nix/MacOS
java -cp .:antlr-3.2.jar BoolExpParser "false and true or true"
Terence Parr's ANTLR reference is the book on ANTLR. And Scott created some excellent video tutorials on ANTLR 3 (with Eclipse).