Better (or at least correct) compilations for conditional assignments

[satyr]

$ coffee --no-wrap -pe 'x[++i][++i][++i] ||= 1'
var _ref, _ref2, _ref3;
x[(_ref = ++i)][(_ref2 = ++i)][(_ref3 = ++i)] || (x[_ref][_ref2][_ref3] = 1);

This shouldn't need more than two temporary variables. The better way is:
var _ref, _ref2;
(_ref = x[++i][++i])[_ref2 = ++i] || (_ref[_ref2] = 1);
Also this:
$ coffee --no-wrap -pe 'x[++i] ?= 1'
var _ref;
x[(_ref = ++i)] = (typeof x[_ref] !== "undefined" && x[_ref] !== null) ? x[_ref] : 1;
should be:
var _ref, _ref2;
(_ref = x[_ref2 = ++i]) == null ? x[_ref2] = 1 : _ref;
And this:
$ coffee --no-wrap -pe 'a.b?.c||=1'
(a.b == null ? undefined : a.b.c) || (a.b == null ? undefined : a.b.c = 1);
should be:
(_ref = a.b) == null ? undefined : _ref.c || (_ref.c = 1)
Then this (which isn't even correct):
$ coffee --no-wrap -pe 'a.b?.c?()'
var _ref, _ref2, _ref3;
(typeof (typeof (_ref3 = ((_ref2 = (_ref = a.b)))) === "undefined" || _ref3 === null) ? undefined : _ref3.c === "function" ? _ref == null ? undefined : _ref.c() : undefined);
should be:
var _ref;
(_ref = a.b) == null ? undefined : typeof _ref.c !== "function" ? undefined : _ref.c()
(hmm, aren't they horrible...)

Patch to come.

[satyr]

http://github.com/satyr/coffee-script/tree/733

ValueNode with soak now delegates its compilation to IfNode by turning a?.b into if a? then a.b.
Similarly, a ?= b now delegates to a ? a = b.