[Haskell-beginners] Need some understanding on this behavior.

Alexander Klink alexander at klink.name
Mon Feb 3 08:59:47 UTC 2020

Hi Alexander,

On Mon, Feb 03, 2020 at 09:14:24AM +0100, Alexander Chen wrote:
> I need some understanding on the following behavior:
> a = [1..]
> [x | x <-a, x <= 100]
> [1,2,3,4,5,6,7,8,9,10,11,12,13,14,15,16,17,18,19,20,21,22,23,24,25,26,27,28,29,30,31,32,33,34,35,36,37,38,39,40,41,42,43,44,45,46,47,48,49,50,51,52,53,54,55,56,57,58,59,60,61,62,63,64,65,66,67,68,69,70,71,72,73,74,75,76,77,78,79,80,81,82,83,84,85,86,87,88,89,90,91,92,93,94,95,96,97,98,99,100
> (note the missing ']' which results in the command not finishing)

It does not finish because the list comprehension does not know that a
is ordered, so it has to go through *every* element and take those that
are less than or equal to 100.


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