@amirshim: Yes, range comprehensions were recently optimized to remove direction-checking when possible. On CoffeeScript master ... x for x in [-10..10]

@amirshim: Yes, range comprehensions were recently optimized to remove direction-checking when possible. On CoffeeScript master ... x for x in [-10..10] ... compiles into: var x; for (x = -10; x <= 10; x++) { x; } Even if the start/end values are variables, the check can be avoided by specifying the step as a number. It'll go out with the next release.