Invalid JS: return if not x? creates empty if block

[colinhowe]

We have some code like:

return if not x?

And this generates:

if (!(x != null)) return

As I understand it, this should output:

if (x == null) return

Or am I missing something unusual about JS? :)

[satyr]

Interestingly:

$ coffee -bce '(x) -> return unless x?'
// Generated by CoffeeScript 1.3.2-pre

(function(x) {
  if (x == null) {

  }
});

$ coco -bce '(x) -> return if not x?'
(function(x){
  if (x == null) {
    return;
  }
});

[goto-bus-stop]

CoffeeScript reads not x as !x, no matter what x is... perhaps unary ! should call .invert, like unless, but that's not exactly congruent with JS and stuff

[osuushi]

Why not just make "if not" specifically synonymous with "unless"? Are there cases where they should not be equivalent?

[michaelficarra]

See #1393.

[GeoffreyBooth]

Even more minimal case:

-> return if yes

---

(function() {
  if (true) {

  }
});

[connec]

This seems like some kind of optimisation. If there's anything after the return if yes line everything is fine.

Example

->
  return if yes
  'hello'

---

(function() {
  if (true) {
    return;
  }
  return 'hello';
});

[vendethiel]

The optimization is in Block, which is an If's @body.

[defiled]

The phrasing on this one is a bit strange and can lead to confusion. Heres an example:

return 'Please enter a number.' if not consumer.number? or consumer.number.length is < 9

So this is saying to return an error message of "Please enter a number" when the two specified conditions have been met. The first one being that there is no data in consumer.number?. The second condition checks for valid data, so it doesn't take any strings with a length less than 9.

[GeoffreyBooth]

I can’t seem to write a test for this. Returning void (i.e. a plain return statement) produces the same return value as a function that doesn’t return. So

(function() {
  if (true) {

  }
})();

is the same, really, as

(function() {
  if (true) {
    return;
  }
})();

And as @connec wrote, as soon as you put a value anywhere (return 1 if yes, or a second return after the line with the if yes) it compiles as we’d expect.

So I guess this is just an optimization that works. It’s a bit confusing to read, but -> return if yes is such a weird edge case that we shouldn’t do anything special here just for readability.

As for the question about the readability of if not versus unless, I don’t think the generated output is confusing enough to justify revision.

So I don’t see anything here that needs fixing. Please comment if I’m wrong, and I’ll reopen.