It seems like a simple conversion, but I can't seem to find the syntax for it.
i = start
while(if step > 0 then i < end else i > end)
array.push i
i += step
start, end, and step are a signed integers
2 Answers
This may do what you want, assuming that you want the numbers from start to end as items in the array variable:
array = (i for i in [start...end])
Comments
You should read the CofeeScript page on loops. But the way to do this in CoffeeScript is with a list comprehension iterating over a range:
(array.push i for i in [start...end] by step)
But note that a list comprehension returns a value. For instance, given this code:
start = 10
end = 5
step = -2
array = []
(array.push i for i in [start...end] by step)
The variable array winds up with the value [10,8,6], as expected, but since push returns the new length of the array it just pushed onto, the return value of that last statement - which will be returned if it's the last thing in a function, or printed if you enter the above at the REPL, etc. - is [1, 2, 3].
EDIT So it would be better, as noted below, to just construct the array with the list comprehension in the first place:
array = (i for i in [start...end] by step)
When building a range, note that ... yields an exclusive range in terms of the right endpoint, while .. yields an inclusive one. So [1..5] includes 5 in the list, while [1...5] stops at 4.
Also, if you really find yourself needing the flexibility of the C-style for loop, you can always embed some literal JavaScript in your CoffeeScript by wrapping it in backticks (`...`):
`for (i=start; (step > 0 && i < end) || (step < 0 && i > end); i+=step) {
array.push(i);
}`
5 Comments
yz10
that is the equivalent of while(if step > 0 then i <= end else i >= end) but, I need while(if step > 0 then i < end else i > end)
Mark Reed
@user842893 - change the dots in the range. [a..b] is inclusive, [a...b] is exclusive. I'll edit.
yz10
I just would like the fine control of the while loop, in the cleaner syntax of the for loop. I don't know if coffee script allows that.
Mark Reed
@user842893 - you can always break into native JavaScript for the extra flexibility if you really need it somewhere. Added an example of that, too.
loganfsmyth
@MarkReed Your solution will work, but as you said, the loop returns a value. You take out the
array.push and use the return value of the loop directly. array = (i for i in [start...end] by step).
stepis1andstartis0andendis0you'll end up in an infinite loop. So it does matter how those are initialized before the loop, and this may be important for converting the code.