Adds method init to Operator class

src/operators/operator.h

@@ -35,11 +35,12 @@ class Operator {
         param(param),
         negation(negation) { }
 
-
+    virtual ~Operator() { }
     std::string op;
     std::string param;
     bool negation;
 
+    virtual bool init(const char **error) { return true; }
     virtual bool evaluate(Assay *assay);
     virtual bool evaluate(Assay *assay, const std::string &str);
     static Operator *instantiate(std::string op);

src/parser/seclang-parser.yy

@@ -261,8 +261,14 @@ expression:
     audit_log
     | DIRECTIVE SPACE variables SPACE OPERATOR SPACE QUOTATION_MARK actions QUOTATION_MARK
       {
+        Operator *op = Operator::instantiate($5);
+        const char *error = NULL;
+        if (op->init(&error) == false) {
+            driver.parserError << error;
+            YYERROR;
+        }
         Rule *rule = new Rule(
-            /* op */ Operator::instantiate($5),
+            /* op */ op,
             /* variables */ $3,
             /* actions */ $8
             );