Solution to Exercise 2.80

[clean99]

function install_javascript_number_package() {
    // ...
  
    put("is_equal_to_zero", "javascript_number",
          x => x === 0);
  
    // ...
}

function install_rational_package() {
    // ...
  
    function is_equal_to_zero(x) {
        return numer(x) === 0;
    }
  
    put("is_equal_to_zero", "rational",
           is_equal_to_zero);
  
    // ...
}

function install_complex_package() {
    // ...
  
    function is_equal_to_zero(z) {
        return real_part(z) === 0
               ? imag_part(z) === 0
               : false;
    }
  
    put("is_equal_to_zero", "complex",
            is_equal_to_zero);
  
    //...
}