"do" for loop

[schloerke]

I find myself writing the coffee-script do function inside a lot of for loops on the given item of the loop.

Current setup:

for item, itemPos in arr
  do (item, itemPos) ->
    # closure stuff

for k,v of obj
  do (k,v) ->
    # closure stuff

I propose modifying the for setup to keep the nice syntax of the for loop

dofor item, itemPos in arr
  # closure stuff

dofor k,v of obj
  # closure stuff

Both would still compile to the same functionality.

var item, itemPos, k, v, _fn, _fn1, _i, _len;

_fn = function(item, itemPos) {
  // closure stuff
};
for (itemPos = _i = 0, _len = arr.length; _i < _len; itemPos = ++_i) {
  item = arr[itemPos];
  _fn(item, itemPos);
}

_fn1 = function(k, v) {
  // closure stuff
};
for (k in obj) {
  v = obj[k];
  _fn1(k, v);
}

[paulmillr]

-1 for new syntax.

I'm using array methods for this thing which resolves problems.

[1, 2, 3, 4, 5].forEach (item, index) ->
  console.log('hello', item, index)

[connec]

Not opposed to sytax further simplifying this, but you can already put it on one line, and it makes it explicit that there's a closure there.

for item in [1, 2, 3, 4, 5] then do (item) ->
  console.log item

_ref = [1, 2, 3, 4, 5];
_fn = function(item) {
  return console.log(item);
};
for (_i = 0, _len = _ref.length; _i < _len; _i++) {
  item = _ref[_i];
  _fn(item);
}

[schloerke]

@connec Now that you point this out, I was mainly looking for a single line setup that gives me closure. Thanks for the then tip! I didn't see an exact example on the intro page, but it makes perfect sense now.

Showing that it has closure with the function directly >> less syntax.

[OnesimusUnbound]

I've search for do'ed for for loop on CS site and this feature does not appear. This appears to be undocumented. Tagging #1808

[lehni]

I was not aware that this was already possible:

for item in [1, 2, 3, 4, 5] then do (item) ->
  console.log item

But I would like to propose a simplification, which would make the code nicer, and might align better with the original proposal. Simply remove the need for 'then' in this case:

for item in [1, 2, 3, 4, 5] do (item) ->
  console.log item

And perhaps, this syntax would then implicitly pass on the for loop variables, e.g. this code in current notation:

for item, index in [1, 2, 3, 4, 5] then do (item, index) ->
  console.log index, item

Would become:

for item, index in [1, 2, 3, 4, 5] do ->
  console.log index, item