ANTRL simple grammar and Identifier - antlr

Question

I wrote this simple grammar for ANTLR
grammar ALang;
#members {
public static void main(String[] args) throws Exception {
ALangLexer lex = new ALangLexer(new ANTLRFileStream("antlr/ALang.al"));
CommonTokenStream tokens = new CommonTokenStream(lex);
ALangParser parser = new ALangParser(tokens);
parser.prog();
}
}
prog :
ID | PRINT
;
PRINT : 'print';
ID : ( 'a'..'z' | 'A'..'Z' )+;
WS : (' ' | '\t' | '\n' | '\r')+ { skip(); };
Using as input:
print
the only token found is a token of type ID. Isn't enough to put the PRINT token definition right before the ID definition?

Answer 1

ALang.g:21:1: The following token definitions can never be matched because prior tokens match the same input: PRINT
Yes, that is enough. If you define PRINT after ID, ANTLR will produce an error:
ALang.g:21:1: The following token definitions can never be matched because prior tokens match the same input: PRINT
I'm so sorry, i didn't want to use this production: PRINT : 'print '; but the production without the trailing space: PRINT : 'print'; The problem is that 'print' is derived from ID and not from PRINT
No, that can't be the case.
The following:
grammar ALang;
#members {
public static void main(String[] args) throws Exception {
ALangLexer lex = new ALangLexer(new ANTLRStringStream("sprint print prints foo"));
CommonTokenStream tokens = new CommonTokenStream(lex);
ALangParser parser = new ALangParser(tokens);
parser.prog();
}
}
prog
: ( ID {System.out.printf("ID :: '\%s'\n", $ID.text);}
| PRINT {System.out.printf("PRINT :: '\%s'\n", $PRINT.text);}
)*
EOF
;
PRINT : 'print';
ID : ('a'..'z' | 'A'..'Z')+;
WS : (' ' | '\t' | '\n' | '\r')+ {skip();};
will print:
ID :: 'sprint'
PRINT :: 'print'
ID :: 'prints'
ID :: 'foo'
As you see, the PRINT rule does match "print".