Add --> operator for non-returning functions

[L8D]

If you don't want this feature, I totally understand and you can close this PR. I'm just doing this since I've already written the code for personal use.

[bjmiller]

What's the use case for this? I'm not sure why I would need to make a function "non-returning". In JS, every function returns something - undefined if you don't use a return statement. If you really want that behavior, just make the last line of a function void 0.

[L8D]

In a lot of my JavaScript projects most of my functions aren't supposed to return anything. A lot of the time CoffeeScript will end up writing extraneous code in order for the last line of a function to return something. By having this operator I can make it a lot easier to distinguish between functions that aren't needing to return something and functions that do. This is very common when it comes to callbacks in Node.js or when working with libraries like Angular.js or Ember.js.

For example, let's say I have a function that calls another function for a specified number of times:

doTimes = (x, f) ->
  for _ in [0..x]
    f()

Well, if you're not careful, CoffeeScript will end up generating this:

var doTimes;

doTimes = function(x, f) {
  var _, _i, _results;
  _results = [];
  for (_ = _i = 0; 0 <= x ? _i <= x : _i >= x; _ = 0 <= x ? ++_i : --_i) {
    _results.push(f());
  }
  return _results;
};

Which you really don't need. The only “proper” way to do this is by explicitly returning at the end of a function like so:

doTimes = (x, f) ->
  for _ in [0..x]
    f()
  return

That can start to make your code look really hairy after nesting callbacks or having non-returning methods on classes.

I made this adjustment to the CoffeeScript library used on a few of my projects to keep my code cleaner and to prevent unexpected behavior when forgetting to add a return at the end of every function.

So instead of writing an additional line, I could just add an additional hyphen.

doTimes = (x, f) -->
  for _ in [0..x]
    f()

And BTW, using an empty return is better than using void 0 or undefined, as CoffeeScript won't realize that's what the function will return anyways, and will actually add return void 0; at the end of the function calls.

Which, I don't really see why CoffeeScript generates this:

var doTimes;

doTimes = function(x, f) {
  var _, _i;
  for (_ = _i = 0; 0 <= x ? _i <= x : _i >= x; _ = 0 <= x ? ++_i : --_i) {
    f();
  }
};

–when all it really needs to do is:

var doTimes = function(x, f) {
  for(var i = ; i < x; i++) {
    f()
  }
};

[L8D]

Step -->
  fs.readFile __filename, this

, (err, text) ->
  throw err if err
  do text.toUpperCase

, (err, newText) -->
  throw err if err
  console.log newText

As opposed to:

Step ->
  fs.readFile __filename, this
  return
, (err, text) ->
  throw err if err
  do text.toUpperCase
, (err, newText) ->
  throw err if err
  console.log newText
  return

[vendethiel]

Thanks for your pull request, but I'm afraid this has been turned down many times already. I guess #899 is the oldest, but the opinion around hasn't changed since I think (issues like this get created regularly and get closed for the same reasons). Closing for now.