如何在ANTLR语法中用括号定义逻辑运算符

Question

I am defining a grammar in ANTLR that will express an expression which includes logical operator and parenthesis together.
Here is the grammar

grammar simpleGrammar; 

/* This will be the entry point of the parser. */ 

parse 
    :   
        expression EOF 
    ; 
expression 
    :   
        expression binOp expression | ID | unOp (expression) | '(' expression ')' 
    ; 
binOp 
    : 
        ('AND' | 'OR')  
    ; 
unOp 
    : 
        'NOT' 
    ; 
ID      :   
        ('a'..'z' | 'A'..'Z')+  
    ; 

The defined grammar can able to express parse tree without parenthesis but when I input an example with parenthesis for example, (Apple OR Bananana)AND Orange It is showing MismatchedTokenException
So, It will be really appreciated if someone explains how to define the grammar in order to express the parenthesis.

Answer 1

You forgot to tell ANTLR what to do with whitespace. For example:

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

Add this and you grammar will work.

As a side note, your grammar has the same precedence for the AND and OR operators. And these operators have higher precedence than NOT . As this goes against conventional rules, I'd advise you to write your expression rule like this instead:

expression 
    :   '(' expression ')'            # parenExp
    |   'NOT' expression              # notExpr
    |   expression 'AND' expression   # andExpr
    |   expression 'OR' expression    # orExpr
    |   ID                            # atomExpr
    ;