99 questions/Solutions/3
< 99 questions | Solutions
Jump to navigation
Jump to search
Revision as of 15:12, 13 July 2010 by Wapcaplet (talk | contribs) (Copied solution from 99 questions/1 to 10)
The printable version is no longer supported and may have rendering errors. Please update your browser bookmarks and please use the default browser print function instead.
(*) Find the K'th element of a list. The first element in the list is number 1.
This is (almost) the infix operator !! in Prelude, which is defined as:
(!!) :: [a] -> Int -> a
(x:_) !! 0 = x
(_:xs) !! n = xs !! (n-1)
Except this doesn't quite work, because !! is zero-indexed, and element-at should be one-indexed. So:
elementAt :: [a] -> Int -> a
elementAt list i = list !! (i-1)
Or without using the infix operator:
elementAt' :: [a] -> Int -> a
elementAt' (x:_) 1 = x
elementAt' [] _ = error "Index out of bounds"
elementAt' (_:xs) k
| k < 1 = error "Index out of bounds"
| otherwise = elementAt' xs (k - 1)