How get Expressions using Java Cup for Java Interpreter

Question

I am creating a Interpreter using jflex and cup, but i dont know how to implements a nested statements, if else loops etc. I want to know if i can get a expression inside a statement to analyze it

si ::=
    SI LPAREN ID:id COMMA ENTERO:value RPAREN
    LBRACE
    code_declarators:expre
    RBRACE{:
        if(parser.tabla.obtenerValor(id)==value){
            codeAnalizer.getInstance().data.put("Tipo", "Si");
            codeAnalizer.getInstance().data.put("Lista", codeAnalizer.getInstance().functions.clone());
            codeAnalizer.getInstance().insert(codeAnalizer.getInstance().data.clone());
            codeAnalizer.getInstance().data.clear();
            codeAnalizer.getInstance().functions.clear();
            codeAnalizer.getInstance().execute("IF");
            parser.condition=false;
        }else{
            codeAnalizer.getInstance().data.clear();
            codeAnalizer.getInstance().functions.clear();
            parser.condition=true;
        }
        System.out.println("HOLA: "+expre);
        :} 
    ;

I need to get "expre" to know and analyze the code inside the statement