antlr4 nodes without labels-CodePudding

I am parsing the grammar with Antlr 4 (v4.9.2)

The following is the grammar:

grammar Test;

start
:
    command  EOF
;
command: commandType params ;
commandType: 'DISPLAY' ;
params: param (',' param)*
    | ;//parameter list
param: ID;
ID : [a-z] [a-z0-9]*
;
WS
:
    [ \t\r\n]  -> skip
;

The input text for the grammar is:

DISPLAY hello, really, sdfdsf
DISPLAY one more now

The following is the parse tree generated. (start (command (commandType DISPLAY) (params (param hello) , (param really) , (param sdfdsf))) (command (commandType DISPLAY) (params (param one))) more now )

The nodes "more now" is not labelled.

Why the parser did not throw error for "more now"?

CodePudding user response：

It does produce an error, but ANTLR's default strategy is to (try to) recover from invalid input, and continue parsing.

This is what is displayed when trying to parse your input:

Try Google for "ANTLR error strategy", "ANTLR error handling", or look at this Q&A: Handling errors in ANTLR4