PFP Laboratory 3

High-order functions

• Create a function that takes a string and converts all characters to upper case letters.

allToUpper :: String -> String

*Main> allToUpper "aAbc"
"AABC"

import Data.Char

allToUpper :: String -> String
allToUpper xs = [toUpper x |x<-xs]                     

allToUpper' :: String -> String
allToUpper' xs = map toUpper xs

• Implement the quicksort algorithm. As a pivot use always the first element in the list. For dividing the list, use the function filter.

quicksort :: (Ord a) => [a] -> [a]

*Main> filter (<5) [1..10]
[1,2,3,4]

*Main> quicksort [1,5,3,7,9,5,2,1]
[1,1,2,3,5,5,7,9]

quicksort :: (Ord a) => [a] -> [a]
quicksort [] = []
quicksort (x:xs) = let lp = filter (< x) xs
                       rp = filter (>= x) xs
                   in quicksort lp ++ [x] ++ quicksort rp