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countSomething.hs

-- Skriv en funktion der returnerer strengen:
--   This is an amazingly interesting sentence!
???

-- Skriv en funktion der returnerer hvor mange gange a findes i [a]
countSomething :: Eq a => a -> [a] -> Int
countSomething ???

-- Skriv ovenstående funktion i 3 udgaver:
--   1. En der løser opgaven med list comprehension
--   2. En der løser opgaven med filter
--   3. En der løser opgaven med foldl

-- Skriv en funktion der returnerer hvor mange gange Char findes i String
countChar :: Char -> String -> Int
countChar ???

sentence :: String
sentence = "This is an amazingly interesting sentence!"

-- [noget] -> noget -> antal af noget
-- [a] -> a -> int
countSomething :: Eq a => a -> [a] -> Int
countSomething as a = length [x | x <- as, x == a]

countSomething' :: Eq a => a -> [a] -> Int
countSomething' x xs = length $ filter (x==) xs

sentence :: String
sentence = "This is an amazingly interesting sentence!"

-- [noget] -> noget -> antal af noget
-- [a] -> a -> int
countSomething :: Eq a => a -> [a] -> Int
countSomething a as = length [x | x <- as, x == a]

countSomething' :: Eq a => a -> [a] -> Int
countSomething' a = length $ filter (a==)

countSomething'' :: Eq a => a -> [a] -> Int
countSomething'' a as = foldl (\acc x -> if x == a then acc + 1 else acc) 0 as

-- Skriv en funktion der returnerer hvor mange gange Char findes i String
countChar :: Char -> String -> Int
countChar = countSomething

countInt :: Int -> [Int] -> Int
countInt = countSomething