Haskell: Pattern Matching with Lists
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Published on 2012-10-06T21:34:41Z
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2012/10/06
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I'm trying to make a function that takes in a list, and if one of the elements is negative, then any elements in that list that are equal to its positive counterpart should be changed to 0. Eg, if there is a -2 in a list, then all 2's in that list should be changed to 0.
Any ideas why it only works for some cases and not others? I'm not understanding why this is, I've looked it over several times.
changeToZero [] = []
changeToZero [x] = [x]
changeToZero (x:zs:y:ws) | (x < 0) && ((-1)*(x) == y) = x : zs : 0 : changeToZero ws
changeToZero (x:xs) = x : changeToZero xs
*Main> changeToZero [-1,1,-2,2,-3,3]
[-1,1,-2,2,-3,3]
*Main> changeToZero [-2,1,2,3]
[-2,1,0,3]
*Main> changeToZero [-2,1,2,3,2]
[-2,1,0,3,2]
*Main> changeToZero [1,-2,2,2,1]
[1,-2,2,0,1]
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