CODEWITHSUNDEEP
listhaskellrecursion
user3588998
user3588998

Reputation: 25

Recursive Function on a List in Haskell

I want to get the max and min value out of a List as a tuple by using recursion. I tried it with this code below and cant really figure out why it does not work. I would really appreciate a small hint what my error in reasoning is. Thanks much

seekMaxMin :: [Double] -> (Double,Double)
seekMaxMin [] = (0,0)
seekMaxMin [x] = (x,x)
seekMaxMin (x:rest) = (max x(seekMaxMin rest), min x(seekMaxMin rest))

Upvotes: 2

Views: 508

Answers (2)

monocell
monocell

Reputation: 1441

seekMaxMin returns a tuple of both the min and the max, but in your last equation you pretend first that it only returns the max and secondly that it only returns the min. You can use a pattern to extract them both and get rid of the redundant walk down the list as well.

seekMaxMin (x:rest) = (max x rmax, min x rmin)
    where (rmax, rmin) = seekMaxMin(rest)

I'm also a little bit opposed to making the min of an empty list of doubles be 0, but perhaps it's suitable for whatever purpose you have with this function.

Upvotes: 5

ars-longa-vita-brevis
ars-longa-vita-brevis

Reputation: 735

Monocell's answer is the one I'd recommend. However, looking at your code, I think the logic you might have been thinking of is:

seekMaxMin :: [Double] -> (Double,Double)
seekMaxMin [] = (0,0)
seekMaxMin [x] = (x,x)
seekMaxMin (x:rest) = (maximum $ x:[fst $ seekMaxMin rest], minimum $ x:[snd $ seekMaxMin rest])

Upvotes: 0

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