can an element contain attribute as parsed by parser generated by ANTLR? if so, how?

Question

I am following this tutorial and successfully replicated its behavior except that I am using Antlr 4.7 instead of the 4.5 that the tutorial was using.

I am trying to bui

Answer 1

I am guessing I need to change the todo.g4 and then re generate the parser.

Of course regenerate after each change. For me it's :

$ a4 Question.g4
$ javac Q*.java
$ grun Question elements -tokens -diagnostics t.text

where

$ alias
alias a4='java -jar /usr/local/lib/antlr-4.6-complete.jar'
alias grun='java org.antlr.v4.gui.TestRig'

The more you describe specific contents, the more you may face ambiguity problems. For example, you have two rules :

payment   : 'pay' [payee] [amount]
free_text : ... any character ...

Consider the following content :

* pay Federico Tomassetti 10 € for the tutorial

* pay Federico Tomassetti 10 is ambiguous and can be matched by the two rules, but it will finally be parsed as free text, because of € for the tutorial which doesn't satisfy payment.

If later you change the payment rule to accept more info after the amount :

payment   : 'pay' [payee] [amount] payment_info

the above content will be matched by payment (in case of ambiguity ANTLR chooses the first rule). The good news is that ANTLR 4 is very strong to disambiguate, it reads the whole file if necessary.

For ambiguous tokens and precedence rules, read the posts of these last three weeks, a lot have been said.

Mixing Raven's grammar with yours, this is one possible solution :

File Question.g4

grammar Question;

elements
@init {System.out.println("Question last update 1432");}
    : ( element | emptyLine )* EOF
    ;

element
    : '*' content NL
    ;

content
    : payment   //{System.out.println("Payement found " + $payment.text);}
    | free_text {System.out.println("Free text found " + $free_text.text);}
    ;

payment
    : PAY receiver amount=NUMBER
      {System.out.println("Payement found " + $amount.text + " to " + $receiver.text);}
    ;

receiver
    : surname=WORD ( lastname=WORD )?
    ;  

free_text
    : ( WORD | PAY | NUMBER )+
    ;

emptyLine
    : NL
    ;

PAY    : 'pay' ;
WORD   : LETTER ( LETTER | DIGIT | '_' )* ;
NUMBER : DIGIT+ ( ',' DIGIT+ )? ( '.' DIGIT+ )? ;  

NL  : [\r\n]
    | '\r\n' 
    ;
//WS  : [ \t]+ -> skip ; // $payment.text => payAcmeCorp123,789.45
WS  : [ \t]+ -> channel(HIDDEN) ; // spaces are needed to nicely display $payment.text

fragment DIGIT  : [0-9] ;
fragment LETTER : [a-zA-Z] ;

File t.text

* play with ANTLR 4
* write a tutorial
* pay Acme Corp 123,789.45
* pay Banana Inc 700
* pay Federico Tomassetti 10 € for the tutorial

Execution :

$ grun Question elements -tokens -diagnostics t.text
line 5:29 token recognition error at: '€'
[@0,0:0='*',<'*'>,1:0]
[@1,1:1=' ',<WS>,channel=1,1:1]
[@2,2:5='play',<WORD>,1:2]
[@3,6:6=' ',<WS>,channel=1,1:6]
[@4,7:10='with',<WORD>,1:7]
[@5,11:11=' ',<WS>,channel=1,1:11]
[@6,12:16='ANTLR',<WORD>,1:12]
[@7,17:17=' ',<WS>,channel=1,1:17]
[@8,18:18='4',<NUMBER>,1:18]
[@9,19:19='\n',<NL>,1:19]
[@10,20:20='*',<'*'>,2:0]
[@11,21:21=' ',<WS>,channel=1,2:1]
[@12,22:26='write',<WORD>,2:2]
[@13,27:27=' ',<WS>,channel=1,2:7]
[@14,28:28='a',<WORD>,2:8]
[@15,29:29=' ',<WS>,channel=1,2:9]
[@16,30:37='tutorial',<WORD>,2:10]
[@17,38:38='\n',<NL>,2:18]
...
[@56,136:135='<EOF>',<EOF>,7:0]
Question last update 1432
Free text found play with ANTLR 4
Free text found write a tutorial
line 3:26 reportAttemptingFullContext d=2 (content), input='pay Acme Corp 123,789.45
'
...
Payement found 700 to Banana Inc
Free text found pay Federico Tomassetti 10  for the tutorial

As you can see, the € symbol is not recognized. You may need a CONTENT rule similar to FIELDTEXT here, and then you get into trouble ...

Federico's Mega tutorial is a good start. For nitty-gritty details, see The Definitive ANTLR 4 Reference or the online doc from www.antlr.org.

Answer 2

Situation on October 24. 2017 at 19:00 UTC+1.

Your grammar works perfectly. I made a full test in Java.

File Expense.g4 :

grammar Expense;

payments
@init {System.out.println("Expense last update 1853");}
    : (payment NL)*
    ;

payment
    : PAY receiver amount=NUMBER
      {System.out.println("Payement found " + $amount.text + " to " + $receiver.text);}
    ;

receiver
    : surname=ID (lastname=ID)?
    ; 

PAY    : 'pay' ;
NUMBER : ([0-9]+(','[0-9]+)*)('.'[0-9]*)? ;
ID     : [a-zA-Z0-9_]+ ;
NL     : '\n' | '\r\n' ;  
WS     : [\t ]+ -> channel(HIDDEN) ; // keep the spaces (witout spaces ==> paydeltaco98)

File ExpenseMyListener.java :

public class ExpenseMyListener extends ExpenseBaseListener {
    ExpenseParser parser;
    public ExpenseMyListener(ExpenseParser parser) { this.parser = parser; }

    public void exitPayments(ExpenseParser.PaymentsContext ctx) {
        System.out.println(">>> in ExpenseMyListener for paymentsss");
        System.out.println(">>> there are " + ctx.payment().size() + " elements in the list of payments");
        for (int i = 0; i < ctx.payment().size(); i++) {
            System.out.println(ctx.payment(i).getText());
        }
    }

    public void exitPayment(ExpenseParser.PaymentContext ctx) {
        System.out.println(">>> in ExpenseMyListener for payment");
        System.out.println(parser.getTokenStream().getText(ctx));
    }
}

File test_expense.java :

import org.antlr.v4.runtime.ANTLRFileStream;
import org.antlr.v4.runtime.ANTLRInputStream;
import org.antlr.v4.runtime.CommonTokenStream;
import org.antlr.v4.runtime.ParserRuleContext;
import org.antlr.v4.runtime.tree.*;
import java.io.FileInputStream;
import java.io.InputStream;
import java.io.IOException;

public class test_expense {
    public static void main(String[] args) throws IOException {
        ANTLRInputStream input = new ANTLRFileStream(args[0]);
        ExpenseLexer lexer = new ExpenseLexer(input);
        CommonTokenStream tokens = new CommonTokenStream(lexer);
        ExpenseParser parser = new ExpenseParser(tokens);
        ParseTree tree = parser.payments();
        System.out.println("---parsing ended");
        ParseTreeWalker walker = new ParseTreeWalker();
        ExpenseMyListener my_listener = new ExpenseMyListener(parser);
        System.out.println(">>>> about to walk");
        walker.walk(my_listener, tree);
    }
}

Input file top.text :

pay Acme Corp 123,456
pay Banana Inc 456789.00
pay charlie pte 123,456.89
pay delta co 98

Execution :

$ export CLASSPATH=".:/usr/local/lib/antlr-4.6-complete.jar"
$ alias
alias a4='java -jar /usr/local/lib/antlr-4.6-complete.jar'
alias grun='java org.antlr.v4.gui.TestRig'
$ a4 Expense.g4 
$ javac Ex*.java
$ javac test_expense.java 
$ grun Expense payments -tokens -diagnostics top.text
[@0,0:2='pay',<'pay'>,1:0]
[@1,3:3=' ',<WS>,channel=1,1:3]
[@2,4:7='Acme',<ID>,1:4]
[@3,8:8=' ',<WS>,channel=1,1:8]
[@4,9:12='Corp',<ID>,1:9]
...
[@32,90:89='<EOF>',<EOF>,5:0]
Expense last update 1853
Payement found 123,456 to Acme Corp
Payement found 456789.00 to Banana Inc
Payement found 123,456.89 to charlie pte
Payement found 98 to delta co

$ java test_expense top.text 
Expense last update 1853
Payement found 123,456 to Acme Corp
Payement found 456789.00 to Banana Inc
Payement found 123,456.89 to charlie pte
Payement found 98 to delta co
---parsing ended
>>>> about to walk
>>> in ExpenseMyListener for payment
pay Acme Corp 123,456
>>> in ExpenseMyListener for payment
pay Banana Inc 456789.00
>>> in ExpenseMyListener for payment
pay charlie pte 123,456.89
>>> in ExpenseMyListener for payment
pay delta co 98
>>> in ExpenseMyListener for paymentsss
>>> there are 4 elements in the list of payments
payAcmeCorp123,456
payBananaInc456789.00
paycharliepte123,456.89
paydeltaco98

Answer 3

I'm not entirely sure what exactly you want but for the provided examples this grammar should do the job:

payments: (payment NL)* ;  
payment: PAY receiver amount=NUMBER ;  
receiver: surname=ID (lastname=ID)? ;  

PAY: 'pay' ;
NUMBER: [0-9]+ (',' [0-9]+)+ ('.' [0-9]+)? ;  
ID: [a-zA-Z0-9_]+ ;
NL: '\n' | '\r\n' ;  
WS: [\t ]+ -> skip ;

If this is what you were asking for I will add some more explanation if needed...