How to iterate through list of lists in Haskell

Question

What I am trying to do is make a program that will go through a two dimensional square of numbers and find the path that gives the highest total. Starting from the top, valid moves are down, and down left/right if available.

The problem that I am having is I am using this function:

  slice :: [Int] -> Int -> Int -> [Int]
  slice x i k 
    | i > k = []
    | otherwise = (take (k-i+1) (drop (i-1) x))

and this function:

    path :: Board -> [Int]
    path [] = []
    path (x:xs) = (maximum (slice x 3 5 ) : path xs

where a type Board is a list of lists.

Could anyone explain to me how I could use variables instead of the 3 and 5, this way I could get all the combos, and then evaluate which is the best route.

there is a great tool hlint that helps with indentation and ()-errors - cabal install hlint — epsilonhalbe
– epsilonhalbe, Commented Feb 11, 2012 at 23:36

Clark Gaebel · Accepted Answer · 2012-02-11 22:39:28Z

1

Newbie's first attempt :-)

path::[Board] -> Int -> Int -> [Int]
path [] y z = []
path (x:xs) y z = maximum(slice x y z) : path xs y z

edited Feb 11, 2012 at 22:39

Clark Gaebel

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answered Feb 11, 2012 at 22:37

Win Man

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4 Comments

user1204349 Over a year ago

thank you.. Now I'm trying to find the width of the square and make the function cycle through all the possible moves. I need something like a loop, that'll go 1-3, 2-4 ect.

epsilonhalbe Over a year ago

in haskell you rather use recursion or fold/scan for iteration than loops

user1204349 Over a year ago

yeah, im just having trouble finding the right recursive function.

Win Man Over a year ago

@user1204349 - I suggest in that case to start a different thread with that question. And remember to accept the answer if it satisfies your question. Don't overload threads ;-)

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