I think I understand the reason why, but still I find it disturbing that in
this first expression, x has 6 elements:
Prelude> let x = [0,60..359]; y = [0,60..359] in (x, y, map degreesToRadians
y)
([0,60,120,180,240,300],[0.0,60.0,120.0,180.0,240.0,300.0,360.0],[0.0,1.0471975333333332,2.094395066
6666664,3.1415926,4.188790133333333,5.235987666666667,6.2831852])
But if I add a comparison to y, x now has 7 elements:
Prelude> let x = [0,60..359]; y = [0,60..359] in (x, y, map degreesToRadians
y, *x==y*)
([0.0,60.0,120.0,180.0,240.0,300.0,360.0],[0.0,60.0,120.0,180.0,240.0,300.0,360.0],[0.0,1.0471975333
333332,2.0943950666666664,3.1415926,4.188790133333333,5.235987666666667,6.2831852],True)
I. J. Kennedy
On Wed, Jun 17, 2009 at 4:55 PM, Alan Mock
That's because [0,60,..359] is not the same as [0,60..359] :: [Double]. So what you're passing to degreesToRadians is [0.0,60.0,120.0,180.0,240.0,300.0,360.0] and not [0,60,120,180,240,300]. I don't know why the Double version adds another number, though.
On Jun 17, 2009, at 4:35 PM, Aaron MacDonald wrote:
For some reason, the map function returns a list that has one more element
than my input list.
My input list is a range defined by [0, 60..359] (should translate into [0,60,120,180,240,300]).
The function I'm giving to map is defined this way: ----- degreesToRadians :: Double -> Double degreesToRadians degrees = degrees * (pi / 180) -----
This is how I'm calling map overall: -----
map degreesToRadians [0,60..359]
[0.0,1.0471975511965976,2.0943951023931953,3.141592653589793,4.1887902047863905,5.235987755982989,6.283185307179586] -----
As you can hopefully see, there are seven elements instead of six. Getting the length confirms this: -----
length [0,60..359] 6 length $ map degreesToRadians [0,60..359] 7
I do not seem to get this behaviour with the length if I either substitute the degreesToRadians function or substitute the [0,60..359] range.
P.S. Is there a built-in function to convert degrees to radians and vice-versa? _______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners
_______________________________________________ Beginners mailing list Beginners@haskell.org http://www.haskell.org/mailman/listinfo/beginners