class Interpreter{

    void evalProgram(List<StmtNode> program, Map<String, Integer> vars)
        for (StmtNode s:program) evalStatement(s);
    void evalStatemenet(StmtNode s, Map<String, Integer> vars){
        if (s instanceof AssignNode){
            AssignNode ass = s;
            String var = ass.var.text;
            int value = evalExpression(ass.val, vars);
            vars.put(var, value);
        } else if(){

        }
    }
}