Does antlr automatically discard whitespace?-CodePudding

I've written the following arithmetic grammar:

grammar Calc;

program
    : expressions
    ;

expressions
    : expression (NEWLINE expression)*
    ;


expression
    : '(' expression ')'            // parenExpression has highest precedence
    | expression MULDIV expression  // then multDivExpression
    | expression ADDSUB expression  // then addSubExpression
    | OPERAND                       // finally the operand itself
    ;

MULDIV
    : [*/]
    ;

ADDSUB
    : [- ]
    ;

// 12 or .12 or 2. or 2.38
OPERAND
    : [0-9]  ('.' [0-9]*)?
    | '.' [0-9] 
    ;

NEWLINE
    : '\n'
    ;

And I've noticed that regardless of how I space the tokens I get the same result, for example:

1 2
2 3

Or:

1        2
  2 3

Still give me the same thing. Also I've noticed that adding in the following rule does nothing for me:

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

Which makes me wonder whether skipping whitespace is the default behavior of antlr4?

CodePudding user response：

ANTLR4 based parsers have the ability to skip over single unwanted or missing tokens and continue parsing if possible (which is the case here). And there's no default to ignore whitespaces. You have to always specify a whitespace rule which either skips them or puts them on a hidden channel.