ANTLR 4 multiple parser rules in grammar mismatched input 'xxx' expecting 'xxx'

Question

I am newbie to ANTLR4 and DSL. I want to create my DSL. I tried basic demo to get idea of it see here . Now I want to define multiple rules(which will represent one functionality/function in corresponding Java class) under one grammar. Where as in DSL input(text file), I want to consume rules randomly and traverse those rules (trees) only(not all rules).

My grammar:
grammar Hello;
sayHello  : 'hello' STRING ';' ;

welcomeMessage : 'welcome' STRING ';' ;

newTest : 'newhello' STRING ';' ;

STRING : [a-zA-Z]+ ; 

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

---

public static void main( String[] args) throws Exception 
{
    ANTLRInputStream input = new ANTLRInputStream("hello world;"

         + "newhello newworld;" );

    HelloLexer lexer = new HelloLexer(input);
    CommonTokenStream tokens = new CommonTokenStream(lexer);
    HelloParser parser = new HelloParser(tokens);   
    parser.addParseListener(new MyHelloLister());

    // At runtime how to define which tree(parser function to invoke) to generate and traverse.
    // parser. sayHello(); // Error, because not traversed tree, and input is mismatched.
    // parser.welcomeMessage(); 
    parser.newTest();   

}

Error: line 1:0 mismatched input 'hello' expecting 'newhello'

So, I want to know from input DSL file, which rules to invoke. Can anyone briefly give me idea about it ?

Answer 1

Well, you call newTest() . The rule for newTest is this:

newTest : 'newhello' STRING ';' ;

So the parser expects something like "newhello abcdef;". But you passed "hello world;newhello newworld;". That does not start with "newhello", as the error message tells you.

You could change your rule like this (not 100% sure about ANTLR syntax, so you have to try yourself):

newTest : welcomeMessage? 'newhello' STRING ';' ;

Then your example should pass.