example

fn with_email(x){
    x.email is r/^[\w\.\+\-]+\@[\w]+\.[a-z]{2,3}$/;
    return with_email(x);
}

fn person(x){
    x.name is str;
    x.age is #nat number;
    return person(x)
}

fn young(x:person){
    x.age < 30;
    return young(x)
}
fn old(x:person){
    x.age >= 60;
    return old(x)
}
fn middle(x:person){
    x.age >= 30;
    x.age < 60;
    return middle(x)
}

let patricia = person{name=`patricia`, age=35};
console.log(patricia);
patricia.age = 13;
console.log(patricia);
patricia.age = 70;
console.log(patricia);
patricia.email = `[email protected]`;
console.log(patricia);
//when the hastag expression is used the object,  the object can not leave the class
let arnold = #old person{name=`arnold`, age=70};
//this should raise error because an old person age can only be greater than 60
arnold.age = 50


//output
#middle person({'name': 'patricia', 'age': 35})

#young person({'name': 'patricia', 'age': 13})

#old person({'name': 'patricia', 'age': 70})

#old #with_email person({'name': 'patricia', 'age': 70, 'email': '[email protected]'})

#person old({'age': #nat number(60), 'name': 'arnold'})