Earlier quoted context omitted.
One thing I have learnt very well from rewriting a legacy PHP code written by amateur teams is: never ever nest ternary operations. maybe it's only me, but it's really hard to reason about this.
Unfortunately there is no if-expression in JS so sometimes it's awkward _not_ to use ternaries in multi-line statements - for instance, when writing in an expression only context like a string interpolation or JSX. It's also just annoying to not be able to assign conditionally without using it, instead of a more clear and readable if/else. It's one of the more annoying nits of the Algol legacy. Oh, but fully agreed,…
If you want the equivalent of if-expression in JS, I think it is much better to make a separate function with a number of returns.
In this case the function is already there:
function deriv(exp, variable) {
if (is_number(exp)) {
return 0;
}
if (is_variable(exp)) {
if (is_same_variable(exp, variable)) {
return 1;
} else {
return 0;
}
}
if (is_sum(exp)) {
return make_sum(deriv(addend(exp), variable),
deriv(augend(exp), variable));
}
if (is_product(exp)) {
return make_product(deriv(multiplier(exp),
variable),
multiplicand(exp)))
}
return error(exp, "unknown expression type -- deriv");
}