Antlr4 tree parser I have problems with numbers like (9-34)*9-CodePudding

I have created a tree with antlr4.The tree performs the calculation steps, for , -., * and /. The tree works perfectly for positive numbers, my problem is, for negative numbers, like when I enter (9-40)*10 or so, it doesn't work anymore.

My code is:

calculator:
    (d)*| ;
    
c:
    c '*' c | c '/' c | c ' ' c | c '-' c | '(' c ')' | b | a ;
d:
     a '=' c ;

b :   '-'?[0-9] ;         
a: [a-zA-Z][a-zA-Z0-9]*;

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

CodePudding user response：

(please be careful to verify your source before your post. The grammar, as posted, is not valid ANTLR. Probably because you changed rule names to a, b, etc. and forgot to keep Lexer rules uppercase.)

If I assume to be the case, here's a modified grammar to address your problem.

grammar calc
    ;

calculator: (d)*;

c
    : c '*' c
    | c '/' c
    | c ' ' c
    | c '-' c
    | '(' c ')'
    | '-'? NBR // <-- The fix
    | ID
    ;
d: ID '=' c;

NBR: [0-9] ; // <-- removed the '-'?
ID:  [a-zA-Z][a-zA-Z0-9]*;

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

The source of the problem is, that by putting the - in the Lexer rule, ANTLR will match the "-40" as a NBR token, since it's a longer string of characters than "40". The solution is to handle the negation as an alternative in you parser rule for c (aka expression)

It's always a good idea to use the ANTLR tool (aka grun) the the -tokens option to get a dump of your token stream to ensure that your Lexer rules are giving the parser the token stream that it needs.