Solution to Exercise 3.35

[KrNor]

// assuming that math_sqrt can be used
function squarer(a, b) {
    function process_new_value() {
        if (has_value(b)) {
            if (get_value(b) < 0) {
                error(get_value(b), "square less than 0 -- squarer");
            } else {
                set_value(a, math_sqrt(get_value(b)), me);
            }
        } else{
            if(has_value(a)) {
                set_value(b, get_value(a) * get_value(a), me);
            }
        }
    }
    function process_forget_value() {
        forget_value(a, me);
        forget_value(b, me);
        process_new_value();
    }
    function me(request) {
        if (request === "I have a value.") {
            process_new_value();
        } else if (request === "I lost my value.") {
            process_forget_value();
        } else {
            error(request, "unknown request -- squarer");
        }
    }
    connect(a, me);
    connect(b, me);
    return me;
}

Test cases:

const a = make_connector();
const b = make_connector();

squarer(a,b);

probe("a",a);
probe("b", b);

set_value(a, 3 , "user");
// set_value(b, 16, "user");

Output:

"Probe: a = 3"
"Probe: b = 9"
"done"

Output when the first set_value is commented and the second one is not:

"Probe: b = 16"
"Probe: a = 4"
"done"