line 1:0 no viable alternative at input '<EOF>'

[Gaurav Singh]

Hello experts,

I am new to ANTLR4 and really excited to learn this awesome tool. 

I am going through  'The Definitive ANTLR 4 Reference' guide step-by-step, but stuck in section 4.1 : Arithmetic Expression Language. Used the grammar Expr.g4 with some modification:

grammar Expr;

prog : stat+;

stat: expr NEWLINE

| ID '=' expr NEWLINE

| NEWLINE

;

expr : expr ('*'|'|') expr //modified

| expr ('+'|'-') expr //modified

| ID

| INT

| '(' expr ')'

;

ID : [a-zA-Z]+;

INT : [0-9]+;

NEWLINE :'\r'? '\n' ;

WS : [ \t]+ -> skip;

With 'grun' everything is working fine for following inputs (using Windows command prompt):

a. 123

b. (a+b)

But when I tried the generated Parser/Lexer with my own java code:

import java.io.InputStream;

import org.antlr.v4.runtime.ANTLRInputStream;

import org.antlr.v4.runtime.CommonTokenStream;

import org.antlr.v4.runtime.tree.ParseTree;

public class ExpressionTester {

public static void main(String[] args) {

String fileName = null;

if(args.length >0) fileName = args[0];

try {

InputStream input = System.in;

if(fileName != null) input = new FileInputStream(fileName);

ANTLRInputStream charStream = new ANTLRInputStream(input);

ExprLexer lexer = new ExprLexer(charStream);

CommonTokenStream tokenStream = new CommonTokenStream(lexer);

ExprParser parser = new ExprParser(tokenStream);

ParseTree tree = parser.prog();

System.out.println(tree.toStringTree(parser));

} catch (Exception e) {

e.printStackTrace();

}

}

}

 By calling the main() using command line : java Expressiontester 1

^Z

Output : 

      line 1:0 no viable alternative at input '<EOF>'

      <prog stat>

Kindly help. The problem arise when I pass the file t.expr as argument.

Thanx in advance.

       

[Gaurav Singh]

I got the glitch. I was passing the input as an argument to main() through command line.

It is working perfectly when I did like :

 java Expressiontester

(a+b)

^Z

output : (prog (stat (expr( (expr (expr a) + (expr b)) )) \r\n))