ANTLR Grammar for a recursive expression

Question

I have problem where I need to validate a set of inputs against a business rule.

The set of inputs can be represented by a class like

public class RuleInput{
    public String payType;
    public String bank;
    public String brand;

    //....Getters and setters
}

My system client can configure many rules in my system. To configure rule i have defined a DSL like below

RULE1 - payType in ('NB,'CC') and bank in ('HDFC', 'CITI')
RULE2 - payType in ('NB') and (bank in ('HDFC','AXIS') or brand in ('VISA'))

Now Given ruleInput = RuleInput(NB,HDFC, VISA) and function

public boolean validateAgainstRule(String ruleId, RuleInput input);

Calling this like validateAgainstRule("RULE2" , ruleInput) should return true;

I am thinking of using ANTLR for the same(But I am very new to it). I tried to build a grammar like this

expression : 
    primary_expression
    | expression OR expression
    | expression AND expression
    | LPAREN expression RPAREN
    ;

primary_expression : //A simple expression
    simple
    ;

simple : TAG_EXPR | BIN_EXPR ;

TAG : 'payment_type' | 'issuer' | 'brand' ;
BIN_TAG : 'bins' ;

BIN_EXPR : BIN_TAG IN BIN_LIST ;
TAG_EXPR : TAG IN LIST ;

LIST : LPAREN TEXT (COMMA TEXT)* RPAREN ;
BIN_LIST :  LPAREN BIN (COMMA BIN)* RPAREN ;

IN : 'in' ;
OR : 'or' ;
AND : 'and' ;

LPAREN : '(' ;
RPAREN : ')' ;

COMMA : ',' ;
TEXT : [A-Z]+ ;
BIN : [0-9][0-9][0-9][0-9][0-9][0-9] ;

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

Can somebody help me to write the grammar for my requirement. I think I need even to use actions in the grammar for accepting inputs.

Note : I even thought of using drools, but I only have a single kind of rules, it will be heavy to use drools for this kind of a small problem. So thought of going with ANTLR only.

Answer 1

There are a couple things I don't understand in your grammar - it doesn't seem to match your DSL...

Here, try this instead:

rule : ID '-' expression ;

expression : '(' expression ')'           # parensExpr
           | expression 'and' expression  # andExpr
           | expression 'or' expression   # orExpr
           | simpleExpr                   # clauseExpr
           ;

simpleExpr : TAG 'in' '(' stringList ')' ;

stringList : STRING (',' STRING)* ;

TAG : 'payType' | 'bank' | 'brand';
STRING : '\'' [A-Za-z0-9]* '\\';
ID: [A-Za-z0-9]+;
WS: [ \t\r\n]+ -> skip ;

ANTLR will generate a base tree visitor class for you, use this to check your expression, or build an AST and check against that (this approach is better but longer to implement).